Bronze Clay?

[GaryR52]

I discovered a product called Silver Clay (http://www.silver-clay.com/), for jewelers, which is composed of 99.9% pure silver in powdered form, suspended in a clay-like binder. You model it like clay, then fire it at a low temperature in a kiln and the binder vaporizes, leaving only the silver. The object shrinks by 30%, so you plan your piece larger than you want the final piece to be.

I was thinking it would be a great idea if they made a bronze version of this for sculptors. You could model a sculpture, fire it like clay and have a finished bronze, ready for a patina, thus bypassing the process and expense of mold-making and casting. However, they don't make a bronze version of the product, so I'm wondering if I could make my own by mixing powdered bronze with a clay-like binder of some kind, or perhaps with a microcrystalline wax. If wax is used, the wax would burn out, leaving the fused bronze. Of course, it would have to be very well mixed so the bronze wouldn't be full of holes after the wax burns out. Any thoughts?

Gary

[Arrow]

I was thinking about this too. I was thinking about a mold filled with bronze powder and binder that could be microwaved too fusing temps. Had this idea since I saw this site. http://home.c2i.net/metaphor/mvpage.html

I believe the key to the metalclay is the size and purity of of the metal particles. The average person wouldn't have anyway to grind the metal into the micro sizes. Bronze would have a higher fusing temp and mixture of different types of metals that would complicate the process.

Sinstered bronze gears and parts are possible, but they undergo a high pressure molding process before they enter a furnace for fusing.

[GaryR52]

Thanks for that link, Arrow! Great idea. I've been wondering what to do with the old microwave I've got sitting out in my garage unused. Now I know. :D

Well, I know from my research that metal clay or silver clay, as it's sometimes called, is 99.9% fine silver after firing and the gold is 24K, so, yes, they are very pure. You're right that the means to atomize bronze is beyond the capability of the average person, but that's not necessary, anyway, as atomized bronze powder is readily available. The issue of the metal content is moot, as well, since, once the wax burns out and the bronze is sintered together, you've got pure bronze that is exactly the same bronze as before, only fused. The process of firing it won't change its fundamental composition, just its state. It goes from a powder to a solid.

I'm not sure you're right about that high pressure part, either. I know that rapid metal printing can produce bronze parts (and other metals, as well, including steel) without any pressure applied at any point in the process. Also, in rapid metal printing, there is no furnace used. The metal is laser sintered. But, that's probably a different process than the one you had in mind. It does use atomized metal, though.

I'm really intrigued and excited about the prospect of using a microwave for this. I hadn't even considered it as a possibility. The 1000 C temp quoted in the article (1830 F) is perfect for use with metal clay, which needs to be fired at 1650 F (for PMC+) for 10 minutes, or 1830 F for two hours for the Gold PMC. Since silicon bronze melts at 1780 F, this would be perfect for bronze, as well. Good thing I have a spare microwave, as I'd hate to have any burnt out wax residue all over the inside of the one I cook my meals in. ;)

P.S.: well after reading the article, I'm a little disappointed to learn that the temps attained were the result of using an investment casting mold material that contains graphite and molochite. Obtaining either shouldn't be expensive or difficult, but I was hoping to be able to use the microwave for metal clay, as well as for trying my bronze clay idea. Maybe if I made a box with a ceramic/graphite/molochite shell into which I could place the metal clay object...but, then I wouldn't be able to keep an eye on it. Hmmm....

Gary

[Arrow]

I love fact that David Reid can reach in with his bare hands too invert the investment and molten metal.

Good microwave furnace pic.
http://www.popsci.com/popsci/how2/article/0,20967,1023030,00.html

I wonder how much silicon carbide bricks cost.

[GaryR52]

Well, according to this (http://www.unibrite.com/PL_dENTAL.htm), you can buy 50 lbs of silicon carbide for $87.40 (the black variety. The green costs much more, for some reason). I also found this, but no prices: http://www.alphamaterials.com/silicon_carbide.htm. Silicon carbide bricks are sold as kiln furniture, so they're fairly common.

Gary

[Araich]

That is really clever, using silicon carbide. I'd tried many years ago to make use of a microwave but couldn't work out how to build up such high temperatures.

How well does the inside of the microwave cope with that heat I wonder?

[GaryR52]

I wonder the same, Araich. Meanwhile, I emailed someone at the PMC Guild and he said he didn't think it was a good idea to try it at all. I figured he'd say so, since he began by saying they are reluctant to tell anyone they can do this because they don't want to be held liable for the consequences if someone burns down their kitchen trying it.

I would imagine that, since the silicon carbide absorbs the heat, it would be mostly contained by the bricks. But then, even so, it has to radiate that heat to somewhere, also.

Gary

[Arrow]

More microwaved metal info.

http://www.sciencedaily.com/releases/1999/06/990622055733.htm

"Powder metals do absorb microwave radiation and can be heated and sintered, using microwaves... Because microwave sintering takes less time and lower energy levels, it is cost effective... We obtained essentially fully dense bodies with substantially improved mechanical properties compared to identical bodies sintered in the conventional manner"

Now I'm on the hunt for the right binder formula. I wonder how long before we will see the first Microwave powered fine arts foundries :)

[GaryR52]

Well, that was encouraging. I just wish the author would say
powdered, not "powder metals." ;)

The other article didn't mention the properties of powdered metals that this one does. Now it makes even better sense. So, basically, all I'd need is some powdered bronze, a binder to mix it with, and some silicon carbide bricks to form an enclosure with. I wonder if you have to completely enclose the piece, or if you can leave a little "window" to view it and reach in to get the part out? It kind of looked that way in the photos that were published with Reid's article.

I'm in favor of microcrsytalline wax as the binder, myself. It's readily available, can be melted down for mixing with the bronze powder, then can be cast in a mold while still liquid. Once cooled, it can be placed in the microwave, where it will readily burn out, leaving the sintered bronze powder. My only concern about wax is that it might burn out too quickly and the bronze, if not sintered yet, could collapse without the wax to support it. Then again, I think the wax burning would probably accelerate the sintering process, so it might work out fine. Other than wax, what could be used as a binder that is relatively inexpensive?

Another thing about using wax is that it can be worked after the bronze powder's been mixed into it, thus, you wouldn't have to pour it into a mold, you could just model it directly. I wonder how easily it would model or carve with bronze powdered infused throughout? It might be a little more dense and less pliable, I would think. But, I remember seeing mention of a product called "gold wax," which is powdered gold suspended in microcrystalline wax and what little I read about it said it's workable by hand.

Gary

[Arrow]

Silicon carbide Rub Brick:

http://www.capcityequipment.com/mbcleaning1365.html

Don't know if this form of silicon carbide brick would work the same as kiln bricks.

Or silicon carbide metal cut-off saw blades. I don't know about the rub bricks, but the blades are bonded with some type of resin that would probably burn.

For support I was thinking a layer of plaster. Sort of like a thin lostfoam coating. A sandbed might aid in support too. That is if the microwaves can penetrate through a sandbed.

[Stevem]

Hey all . I am fairly new to casting, I have been paying the foundries to mold and cast my pieces up untill recently. So at the sake of sounding ignorant, has anyone tried this process? I don't understand how the binder melts out and leaves the powder solid in the same form it was before. Wouldn't the binder melt before the metal? Seems like the wax would melt way before the metal had a chance too! Would this not create a puddle of metal at the bottom? at the very least would this deform the sculpture? I am very intrested in this if it is plausable.

Thanks for any information on this,
my small and inquiring mind would like to know,
Steve Miller

[GaryR52]

Steve, the wax would burn out and the bronze powder would sinter (fuse) together, forming solid bronze. The process would be identical to that used for Precious Metal Clay (Silver Clay), which consists of powdered silver in a resin binder. The piece would be fired in a kiln at a temperature high enough to burn out the wax, but not high enough to melt bronze.

Your response suggests that you're assuming this is a casting process. It is not. The "metal clay" would consist of powdered bronze suspended in either a resin binder or, as I advocated, microcrystalline wax binder. It would be pliable and you'd model your sculpture with it directly. To get a "bronze," you'd then fire the piece in a kiln, vaporizing the binder and leaving only the sintered bronze powder, which becomes solid bronze. The object is not to melt the bronze and pour it into a mold (which would make the whole modeling process pointless). This is intended as a cheap, direct substitute for arriving at a bronze casting, as it totally eliminates the casting process altogether.

I haven't tried this, as there is no such commercially available product; just silver and gold "clays," which are used in jewelry making. They shrink by 30% as the binder vaporizes, leaving behind sintered silver or gold. The same process should be applicable to any metal, though. All you need is powdered metal, suspended in some type of binder that can be easily burned away at relatively low temperatures. You can even "hand fire" Precious Metal Clay with a butane torch. If you substituted bronze powder, the firing temperature would probably have to be modified, but the process and result would be the same. Gold clay fires at a higher temperature than silver clay, so I would imagine bronze clay would fire slightly higher than gold.

Gary

[fritchie]

Steve - At the risk of sounding ignorant myself, because all I know about this process is what I’ve read here, I suspect the rate of heating is critical. The metal particles have to begin fusing together or “sintering” before the clay matrix is gone. If heating is essentially a “flash” process, that could happen.

I’m a little surprised at the high degree of shrinkage, but that probably reflects the maximum amount of metal powder that can be suspended in the matrix, possibly also with heating characteristics in mind. If the metal and the “clay” suspending agent were heated as separate powders with identical heat sources, the metal would heat up to 2 - 4 times faster because it would have a much lower heat capacity.

On the matter of shrinkage, I’m a little puzzled also. We are talking about 3D objects, so a 30% shrinkage in volume is about a 10% linear shrinkage. (That is, a 1 inch diameter ring, for example, would be about 0.9 inches in diameter after sintering. On the other hand, if the shrinkage is 30% in linear measurement, that same 1 inch diameter ring would be about 0.7 inches in diameter. But the volume of a 1 inch cube of this stuff would have a volume of about 0.7 x 0.7 x 0.7 cubic inches after sintering. The volume would be about 0.35 cubic inches instead of 1 cubic inch.

I suspect it’s volume shrinkage that is 30%. And a basic problem is that both silver and gold have much lower melting (fusing) temperatures than bronze. This process might not be feasible with bronze or copper. It might with aluminum, which also has a relatively low melting point.

[GaryR52]

Fritchie, I believe you're right that the shrinkage is 30% by volume, rather than linear. I haven't tried it yet, but, based on what I've read about silver clay, I think that's correct.

You may be right about bronze and copper not being suitable. Again, I don't know, yet. Aluminum powder would be ideal, though.

Gary

[ERB]

Hi,
I have had several pieces "cast" using the sintered bronze process by Aesthetic Materials a "foundry" in State College Pa. I gave them a clay and they made a silicone rubber mold. A compound of wax and bronze was poured into the mold the piece was removed from the mold and "fired". The final bronze shrunk about 10% and was solid metal that could be brazed. The foundry is no longer in busniss. It was owned by a professor at Penn State who holds the patent on the process. I wish they would start up again because the pieces were great ans a fraction of a poured metat foundry.
Dick

[GaryR52]

Thanks, Dick. I had no idea anyone was using this commercially. Well, I guess they aren't anymore, but it is encouraging that someone was using it. It at least proves my theory about using bronze powder suspended in microcrystalline wax actually works, if nothing else.

Gary

[GaryR52]

In the discusssion we had on using a microwave oven as a kiln, there was a link to an article in which the author had used refractory bricks inside the oven to acheive high temperatures. The oven, by itself, isn't capable of temperatures high enough to melt metal.

Gary

[Arrow]

Found little info.

Aesthetic Materials: polymer-powder
http://www.cisp.psu.edu/pdf/nl_summer02.pdf

Randall M. German
http://www4.esm.psu.edu/people/faculty/?ID=RMG4&tabs=cv%7Csrv
Aesthetic Materials (1998-Present


Too busy with NASA/hightech jobs to deal with sculptors :confused:

[Arrow]

hummmm.....


"A process for sintering green powder metal, metal alloy or metal composition parts employing microwave energy is described."

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=6,805,835.WKU.&OS=PN/6,805,835&RS=PN/6,805,835

Direct metal fabrication

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=6,517,773.WKU.&OS=PN/6,517,773&RS=PN/6,517,773

[GaryR52]

I'd like to find out more about Aesthetic Materials, the company mentioned in the PDF. It says they "...simplify the production of bronze art via use of hybrid polymer-powder forming and sintering technologies. The company provides a variety of replication technologies for artists, designers and engineers...", unfortunately, I was unable to find anything on the company.

Gary

[Arrow]

http://centreweb.com/old_sites/aesmat/index.htm

[GaryR52]

Thanks, Arrow! :)

This sounds exactly like what I had in mind. It says you can carve directly in blocks cast from the material. The shrinkage, during sintering, is only 5%, too. One limitation I'm wondering about is the maximum height of 20". I wonder why that is?

They have an intro offer whereby you can order a free block of the material for carving, then send your carving back to them for sintering and they won't charge you for the process. Sounds like a sweet deal.

I'd like to find out if I can fire my own, though. According to another website, "Sintering temperatures can range anywhere between 1450-1550 degrees for bronze." An electric kiln can easily acheive such temperatures and so can a butane torch, so, it's entirely possible to fire your own bronzes. A little experimentation with mixtures of wax and bronze powder can probably duplicate their product, also. It would be cheaper to do so, not to mention faster (there is a 4 week turnaround time using their services).

Gary

[bluedogshuz]

Gary, Did you contact this company? I thought aprevious post stated they were not in business? Sounds great to do smaller pieces particularily if through direct carving vs molds. Also you are probably correct that if you had a large enough kiln you could produce larger works.

[GaryR52]

I haven't contacted them yet, Blue. As for the size factor, that's going to be limited by the confines of the kiln or furnace used for firing and that would explain their maximum height limitation of 20".

Gary

[Arrow]

Pilato Process:
http://www.pilatostudios.com/pages/markSculptureGallery.html

http://www.catskillregionguide.com/articles/article.php?id=396&page=2
"Pilato covers the clay miniature with several layers of silicon rubber, each of ten coats becoming progressively thicker with subsequent applications. In turn, he slathers the rubber mold with ceramic slurry encasements made in sections. These sections are then puzzle-pieced together to create a workable Mother Mold, which is then filled with wax. The wax miniature is then delivered from the Mother Mold and refined and detailed further. This rendition is then dipped in ceramic slurry 13 times, creating a solid, sturdy, layered mold. During the Lost Wax Process, Pilato vaporizes the wax replica and fills the vacant mold with powderized metal that turns to bronze. He then buffs, polishes and patinas the sculpture, producing a portable miniature of the most-often-times life-sized models-to-come.....cutting 20 steps out of bronze foundry processing..."

[GaryR52]

Pilato's process is the lost wax process, Arrow. Not to be confused with what we've been talking about here. In the lost wax process, conventional bronze casting is used; the wax is burnt out when the molten bronze is poured. This is not the same thing as sintering bronze powder suspended in wax. The former is a traditional foundry process, the latter avoids this foundry process by direct modeling or carving in a bronze/wax material which is then fired in a kiln to produce a bronze sculpture. This process eliminates the costs of using a foundry, as anyone with a kiln can do it.

Gary

[Arrow]

Somehow the two are related:

"vacant mold with powderized metal that turns to bronze"

Either the suspended polymer sintering evolved into the "Pilato Process" or vice versa? Not sure. Mark Pilato has the aesmat company referanced on his site resume:

"1998 Inventor of the Pilato Process ( a new process for casting bronze). http://aesmat.com/company.htm"

I'll have to do some more web snooping.

[GaryR52]

I didn't see the reference to "powdered bronze." I'm not sure exactly what he's doing, but it does say "lost wax process" and that is not the same thing as what we've been discussing. The lost wax process of bronze casting is an ancient technique, nothing new about it, and it certainly didn't originate with Pilato. Whatever it is he's doing seems to be a variation on that, but it doesn't sound like the same process we've been talking about here. There is no bronze pouring involved at all in this process, unlike the lost wax method, in which there is. The whole advantage of this process is the elimination of the bronze pour.

Gary

[bluedogshuz]

I called the number on the web site for Aesthetic Materials and it has been disconnected. I assume they are no longer in business. I am very interested in the process of suspending bronze and then firing so I guess I will start doing a process search.

[Arrow]

The part of the process that may make the sintered bronze clay quite difficult is the possible need for a reducing atmosphere inside the kiln/oven. To control the oxidation and binder burnout.

[GaryR52]

Sounds like a good idea, Blue. As soon as I can, I'm going to try my own experiment with it. One word of caution, though; this is basically the same as silver clay, or "Precious Metal Clay," and one thing I've learned about that is that you have to watch the kiln closely because you don't want to exceed the sintering temperature and melt the metal, which would ruin your piece. Some trial and error experimentation with ratios of bronze powder to wax binder, as well as with temperature and perhaps different binder mixtures would seem to be in order.

Gary

[Arrow]

Good pics of a Microwave Sintering Furnace

http://www.linn.de/mikrohaus01.htm

[GaryR52]

Pretty much the same as the one discussed earlier, in another thread. The difference is the material used for the refractory chamber within the oven. Great for jewelry, but pretty limited for application to sculpture, as the space available is way too small for anything I'd want to do.

Gary

[ERB]

Hi Gary,
The sculpture "cast" by AESMAT in State College PA was a very finely powdered bronze mixed with some kind of wax. It was pourable into a rubber mold when hot and hardened into a substance very much like almost dry potters clay. It was carvable and could be patched. They sold blocks of the material that you could carve into a sculpture or medal. The sintering was done in a kiln and the temp. was very critical. Clients were not allowed to see the equipment or the process. The shrinkage was less than 10%. The pieces turned out great. They produced several pieces for me and I had many more for them to do when they stopped doing business. They didn't go out of business for lack of work or money.
Dick

[GaryR52]

Sounds like what I want to do, alright. Too bad they're not doing it anymore. Do you know of anyone else who is?

Gary

[ERB]

Hi,
Sorry no. I wish I did.
Dick

[mark pilato]

Hi my name is Mark Pilato, i invented the Pilato Process. If you have any questions i can help. I would love to see more artist use it. The company that bought it from me was not interested in the art part just the manufacturing end of it. I have it back and I will share any info you want. Here is a link to chess sets I used the Pilato process, It would have been very hard to get the detail casting them plus I also can weld plus patina also the cost is about 50.00 and one night in a Kiln. Oh and did I mention the work on the bronze is about ten minutes a piece when they come out, no vents gates, sprues, sand blasting, and the patinas are perfect.
http://www.pilatostudios.com/pages/markChessSets.html
all the best,
Mark

[Arrow]

Can you describe the process and components in detail? Or are you retaining proprietary control? Which is understandable.


P.S. Thanks for finding the forum :) As you can see from the past posts there are several people craving info on your process.

[HappySculpting]

Hi Mark,

Sounds like a very interesting process and I would be grateful too if you could describe more about it. Sounds like one of the biggest differences is that you use a bronze powder mixture that fills the mold and this cast is then fired to solidify the whole piece. So there aren't any sprues etc.

I have a kiln and wondered what temperature you have to fire the bronze powder to?

Where does a person get this bronze mixture that is poured in? What are the ingredients? The mixture is room temperature when poured in, right?

Since a lot of us use bronze foundries, I'm sure there is much interest on a more hands on approach that we can do ourselves to reduce costs. Thanks for offering your expertise! :)

[mark pilato]

very cool, the process is very simple but also very sensitive, it took me and two other scientists two years to perfect. I am dyslexic so I apologize for spelling. I created the process in my living room because I was always disappointed with the finished product of a lost wax. Don't get me wrong I use the lost wax process today and for larger works its the only way but for smaller works, studies, chess pieces, and any size relief this process is perfect and who knows what you will find and the future will bring . I have been casting work since I was a boy and I had my own foundry when I was 19. Today I use Tallix to cast my work. I invented this process so that people could use it. It is heaven if you are a sculptor, to be able to sculpt in the green clay or bronze then to put it into the kiln and wala the piece is done exactly as you wanted it. To sculpt bronze with a tool not Air or chisel. Sounds to good to be true. Okay enough excitement lets get dirty. So first you need to buy some bronze powder with out oxides, also make sure its variable sizes, from very fine to medium. this is the cheapest way to buy it and by chance the only way to do it. secret # 1. Like a good stone wall it takes interlocking pieces to make it strong. Bare with me. Next you need a kiln with a computer so that you may ramp and hold. Plus you need a stainless steal container that will fit into your kiln leaving a 2 to 3 inch space from brick. You can buy them on line. Okay I am not going to give it all to you right now. But i will, I have to get ready for my daughters 6th birthday party. Here some things to think about. A wax pot, basically a crock pot, A foot massager/ vibrating table. A second hand vacuum furnace 50.00 at salvage yard, oh a very important component, Nitrogen. 25 pounds pressure. Can get at most welding supply companies. 345 c burn out temp then 900-degrees for two hours then cool down 12 hours. Okay tell me what is missing and I will give you the rest. How do the pieces hold their form? Were does the wax go? What is the mix ratio wax and bronze powder. and what do you need the massager for? Like I said I will give it all to you but first i want you to think about it and see if you can come up with it on your own. With this process i could complete a chess set from the rubber mold to finished bronze in 3 days and give it to a scientist when I was done and he or she would say it's cast. how is that possible to take a three week process and shrink it down two three days.
here is my web site
pilatostudios.com

All the best,
Mark

[Arrow]

Does the bronze-wax model require a refractory shell? Or does the binder/wax formula have adequate holding properties all by itself, during the burnout.

My guess on the binder would be a mix of corn starch and some microcrystalline wax??

Have you tried the process with aluminum?

[mark pilato]

I like the way you think, and i like the idea of adding something to the wax. But check this out - so say you have a can just bigger then your sculpture and in that can you place your sculpture - part wax, part bronze and part Empoline a very small part Empoline say 2%. The sculpture is surrounded by a powder that can be re used. this powder absorbs the wax when the kiln is ramped up to its first hold. After wax is pulled out into the powder the kiln is ramped up next level in heat. The wax burn off is exited out a tube where a flame waits to finish the job so that there is no trace of black smoke. What is the powder that can be used? Its white and can be packed by tapping the can onto a level surface. Its very light but also dense. This is the key. this is what gives you the freedom to create any kind of detail. Not a slurry, no dry time, just powder a one step deal. a six inch piece takes 2 minutes to prepare and its ready for the kiln. Small work can be placed on a kiln shelf and just covered with the stuff. We have done over 100 medallions in one run. All came out perfect. So the piece is heated up to a temperature in the can so that the wax can escape into the powder. then after say an hour the kiln is heated to the second hold so that the wax can be burned out. Then the Kiln is ramped up to it's last temp a very precise temp so that it can be sintered but not melted and then let cool. The cans are then dumped and the powder re used. Then the pieces are cleaned in water or bead blasted for a second or so. then if need be polished to any finish and then patina. The best way to know what the temp of the pieces is is to have a can in the coolest place in he kiln filled with the white powder and in that can a pyrometer to gage the temp. How do i put a picture up of the kiln and what it all looks like, this will give you a better idea. The best way to weld is with tig. Again whats your guess on white powder?
All the best,
Mark

[mark pilato]

here are some links
http://www.newscientist.com/article/mg16321962.900.html
http://www.cisp.psu.edu/pdf/NL-Fall05.pdf
I think i can do this in a micrwave. I am going to give it a go and I will let you know.

[Arrow]

I'm afraid your pdf file link told exactly what the white powder is, aluminium oxide. :)

Unless you have modifed the process since. I was going to guess fused silica.

What is Empoline?

So if I outline the steps as the following:
1. Mix up green bronze and binder clay body.
2. Sculpt disired shape.
3. Pack green sculpture in a alumina powder container using vibration table.
4. Wax burnout, ramping phase up to 653 F.

This is where I'm not sure what happens next.
Does the alumina powder and sculpture go into a nitrogen charged furnace for sintering?

Or does the burnout stage pre-bind the object enough to remove the powder support?

[mark pilato]

oops, would you have got there on your own? also the bronze / wax is melted together then poured into rubber molds. the clay is an altogether different process. I have done both. The best way for me to show is to draft a picture for you. The Kiln is a nitrogen charged furnace. from the time the kiln starts Nitrogen is introduced, when pieces are sintered after they have reached temp the Nitrogen can be turned off and kiln can cool down. The key is the the furnace. sometimes the simplest answers are the hardest to find. when we finally found all the answers and got a chess set it was like we landed on the moon and the answer the one detail that alluded us, was in furnace design. I figured it out after two days of maddening reexamination when I was just about to give up, it just came to me and the first sintered bronze chess set was introduced to the world. How do I put a picture up so anyone can see and try? Its is perfect for schools who have a limited budget and for artist who want to cast at home. Epoline is a very hard binder. I am currently creating a new chess set and I plan on sintering the edition. the king is 16 inches and the set has an edition of 12. There really is no other way to do it. when i do this I am making a movie showing the process so anyone can use it. It will be on my web site. When I sold my share of the company I signed a five year contract and was not aloud to use, Now that five years are up and i have it back i am going to share with who ever wants to try, for free.
all the best,
Mark

[Arrow]

I use http://photobucket.com for free image hosting.

[Candice Lee]

Beautiful process, Mark! I’d like to try it. Is there a specific necessary ratio of bronze powder to wax in making the sculpture?

Candice

[mark pilato]

okay, what I am going to do is make a document to share with anyone who wants to try. I am going to get in touch with Rand German, and my other scientist friends who also helped me in this process so that they also can have a chance to share. We all had a dream to change the world of art, as silly as that sounds I still believe its the future and its up to the artist to find the way. I have been very lucky in my life sculpting for a living finding myself in collections with Piccaso Moore,Nevelson and I have seen some amazing things when it comes to art and what lives in peoples hearts. I know how important a process like this would be to people who can not pay the foundries. To be able to sculpt the bronze is a dream come true. what is your web page? I like to know who I am talking with. My e-mail is sculpting2000@catskill.net my web page pilatostudios.com.
all the best,
Mark

[mark pilato]

Candice- just got to your web Page, great sculpture and I love your Philosophy. Yea you would dig this stuff, you would go wild with the form carving and finding deep places.
all the best,
Mark

[Dup-Csapo Reka]

Did anyone think about that wax is burning out untill 300 degrees( Celsius), and bronz, copper and other stuff which are in bronz we do use fuse at 900-1000??What will bronze do untill you reach this degree .Set still and wait?

I cast for 10 years , and still considering myself an apprentice , but this whole thing sounds to me absurd.

Or maybee I missed the point??
:confused:

[Arrow]

The process is sintering: powdery metals become a coherent mass by heating without melting.

Quite different from casting molten bronze. More closely related to ceramics.

The link Mark Pilato provided explains the general process:
http://www.cisp.psu.edu/pdf/NL-Fall05.pdf

[mark pilato]

Hi Reka -sounds crazy but true and yes it does just sit and wait. mind you it is surrounded by a dense powder that helps hold it up wile it is brought to temperature. Thats the beauty of it. think on it for a wile check out the links I gave above. This is the process of the future of bronze and I cant wait to see what people will do with it, its beyond imagination. Glass, Stainless,bronze and who knows, maybe something altogether new. I plan on putting it in hands of artists to see what can be done. It is a dream you know, to sculpt bronze and have it come out exactly the way you like. I have sculpted my whole life and i have never seen anything like it. Its beautiful,simple and clean. If you scroll up you can read about others that used the pilato process and were very pleased. So jump on man its a crazy ride and maybe it will be you who shows us all something fresh- never seen before. You can weld plus patina and i bet if you were to see a piece done by this method you would say "dam thats a good cast". So say you have your rubber mold and you pour this material in the same way you would a wax, then after it has cooled you take out and clean seam line and here the kicker you sculpt the bronze, find deeper undercuts clean edges and create new forms, then to the kiln were the magic happens and wala a finished bronze- no cups -no vents- no shrinkage -no sand or foreign material- I could go on and on. Again sorry about spelling I am dyslexic so this stuff take me a little longer then most.
All the best,
Mark

[dawn]

It sounds unbelievable! Mark, are you really going to share it with all of us here? I know how hard for it is for people to share information like this with others for free, especially when it cost you so much time and effort and money and when probably no one had shared their information with you for free when you were in your process of experiment. Your informatin is definitely valuable. For sharing such valuable information with others, it makes you a truly respectable person that we rarely seen today.

I started doing sculpture only for a few years and yes, I had only cast two of my pieces in bronze because I can't afford it. Therefore I tried all those "fake" procedures like resins, cold-cast stuff, etc. I also hand cast a few pewter at home. So, your invention would be something changing my life. I can't wait to hear more and thank you with all my heart. :)

[mark pilato]

I have done a lot in my life when it comes to helping people and although it's my gift I always feel that I am receiving much more. I also believe like so many, that when you do something good for someone it makes the world a better place. I volunteer teaching people with disabilities and I have seen true miracles when it comes to the power of art and what lives in our hearts. My latest sculpture Ascent is my gift to the families of 9/11. It took three years and I cried a lot in that time. I saw things I would never want to - ever. But do you know what I found - Love. Some would say it was crazy to give it away and they did, I was offered crazy money for it. but for me there was no other way. I learned more in that three years then my whole life. I saw things in the form that were not there before. I traveled to places deep inside me and found new meaning in my life and i am a better person for it. I met heros talked with Families who's stories move me greatly and the most amassing thing my sculpture has helped heal. What more could I ask. So when it comes to sharing a process that would help so many. That may help an artist express ones self and help with in there career and maybe even bring something into the world that is new never seen before. What is money when it comes to this. I know how hard it is, I have been there. I support my family with my art. Its always hard but I live the life and I love it. Its not fun trying to come up with money for the foundries and when your a sculptor its hard to make a living without them. So I know what this will do for so many. As for worrying about what other would do or not do, that takes to much time and we all know what is right. So do good and try not to let others bring you down.
Check out the link
Quick Time
http://www.pilatostudios.com/pages/stpauls_qt_large.html
windows media
http://www.pilatostudios.com/pages/stpauls_wm_large.html

All the best,
Mark

[dawn]

Mark,

I hope more and more people are like you, willing to give a helping hand. Like in this site, people and willing to share informations and their experience. I think it is one of the best site I've ever visited.

BTW, I can't open you PDF link. When could we expect to watch your movie? Please kindly explain each procedure as clearly as possible in your movie as some of us , well, at least me, are quite inexperience even with kiln firing :p .

Dawn

[HappySculpting]

I traveled to places deep inside me and found new meaning in my life and i am a better person for it.

Yes, I'm just getting a glimpse of the kind of guy you are and all of this giving will give to you in return with lots of happiness. You have a beautiful life right now as I can see by the videos- blessed with a wonderful art partner and the cutest kids. Wish you all the best and thanks for sharing this process with us so generously.

Dawn- I was prompted to download Quick Time "Active X" in order to view the first video. These videos are so professional looking. I can see Mark is multi-talented to say the least. There are other videos on his site that show the whole process of him sculpting the "Ascent" that he donated as a 9/11 monument. I need to go back and watch the rest now. ;)

~Tamara

[mark pilato]

Hi I think this may help - I found it on an old web site for Aesthetic Materials. The Fired Bronze Process was invented by Dr. Rand German, Penn State researcher and expert in the field of powdered metals, and Mark Pilato, bronze sculptor. Together they have explored and perfected the process of creating exquisitely detailed, solid bronze sculptures using powdered metals, binders, and sintering.

In this new (patent-pending) process, a proprietary feedstock of powdered metal and binders are mixed into a liquid, which is poured into a rubber mold of the piece to be produced. The mixture is allowed to solidify then the green piece is removed from the mold. (Green pieces can also be carved directly from molded blocks of the mixture.) After molding or carving, the piece is inspected, chased, and prepared for firing.

The firing method used in The Fired Bronze Process is known as sintering, within which the metal particles are heated to a temperature high enough to cause the particles to fuse with one another but not to melt. During the sintering process, the binders holding the green piece together evaporate leaving a piece that is solid bronze -- identical in appearance to foundered bronze. This process is faster, more energy efficient, and less damaging to the environment.

Because the piece can be chased in the green state, little (if any) post-sintering chasing is required. There are no runners or sprues attached to the piece, and surface detail will match the quality of the original mold. Green pieces can be welded, if required. Sintered bronze has excellent surface smoothness and accepts all patina finishes. The process causes shrinkage of about 5%.

Currently, the maximum height of pieces that can be made through The Fired Bronze Process is about 20"; however, the company continues its research and development, which will continue to increase the size of pieces manufactured.

The company employs artisans skilled in the production of rubber molds, and will also accept artists' molds, subject to satisfactory inspection.

[HappySculpting]

Thanks Mark. Can this bronze clay be purchased somewhere? I know that the link that you gave on this showed a website but are they out of business now?

~Tamara

[fused]

If you like forming this type of maleable material --which can be fragile when finished-- I would like to suggest that you consider working in wax. A microcrystaline or something similar for bronze casting. I say this because most clay forms are not typically large and wax does have some similar properties without the negative qualities (dry, brittle,delicate) as you work it. Wax can be worked on anywhere and when cast is a durable finished product.

Working smaller means you can find an independent foundry guy or maybe a local art school sculpture department that could make casting in metal affordible.

Forget about editions and make unique pieces. Potentially you might sell some and they will pay for themselves or even allow you to eventually upgrade your scale. I have friends who trade castings with a commercial foundry to cover all the casting expence of the process for both iron and bronze.

[mark pilato]

Thats a great idea fused - i have traded for castings, I have also sold work for the price of two castings so I would have one to sell, this way the collector is getting a great deal and I am also able to sell one. sometimes I also put a price on work like 5,000 plus casting cost and I have the client pay the foundry direct this way they are not shocked when confronted with a huge amount. One of a kind wax is a really great way to go also. I like sculpting wax in hot water then freezing it so I can sand and make hard edges. Also Try mineral spirits with drywall paper. Tamara the process is not being used right now as far as I know but you may want to try and contact the person on this link and see if anyone is working on it. Tell her you are an artist and talked to me and could she send you a more detailed look at it all. Who knows maybe she will send you everything.
good luck
http://www.cisp.psu.edu/pdf/NL-Fall05.pdf

[dawn]

Mark, I can't open your PDF file.

Are you still planning to share the technique with us by making a movie?

Dawn

[mark pilato]

yes I am planning on making video and sharing for free. , I have to finish sculptures for clients plus a new chess set etc, etc, so it will be some time. I have to make sure that I give all the info so i have been trying to get hold of the other scientists to see if they have any info they would like too share. try this - The persons name I mentioned above for you to contact is Sharon Elder at The Center for Innovative Sintered Products at Penn state her E-mail is cisp@psu.edu I know that when I left my team was working on a small scale kiln that was very economical to use. You may want to ask about this also. Good Luck, Back to the studio to grind away.
Mark

[sparklemachine]

Wow. This stuff is great. Can't wait to try working with it...

[dawn]

I sent an e-mail to Sharon Elder a few weeks ago and another e-mail to Mark Pilato. No reply from either one so far. I wonder if the story ends here.

[mark pilato]

sorry guys, I am very bussy finishing work to suport my family I have ten sculptures that have to be finished so I can put food on the table, maybe Sharon is on vacation until the school year starts again. Have you reached Rand German? I am sure if you try a little harder you will get your anwers, maybe call Penn State and Talk to Sharon directly. Call Penn State ask for Sharons #. When I get the time which will not be for some time I will share. Sorry I have not e -mailed I am in Vermont for two weeks swimming and fishing with my family. Then I go back to the studio to sculpt sculpt sculpt.
all the best,
Mark

[dawn]

Sorry about pushing you. I am just too excited about this new technique to be cooled down. I really want to introduce this technique to HK as I believe many sculptors here could by benefited. Till you have time to share, I'll wait patiently :)

[DanielUCM]

It has been really interesting to follow this thread! I keep getting surprised at how all you people here readily supply hard to come by advice and information to each-other! I was myself thinking of trying to do some liquid-phase sintering with kopper and tin powder mixed with some binder when I found this thread and realised that this Pilato-process appears to be cleaner and better. I for one would have had a hard time to figure out to use aluminum-oxide to encapsulate the sculpture.

I actually experimented with some pre-alloyed 89% copper, 11% tin, powder mixed with mikro-wax to see if it could actually work. I just made a flattened blob of the mix and put it in the aluminum oxid. I used a simple gas-powered furnace and used the steel-container as temperature indicator. The result was a somewhat solid piece of bronze. Since the environment was not full of nitrogen the pieces were heavily oxidised with a lot of scaling and slagg (not sure of the English word?). Beneath all of that was however a thin core of solid bronze, I guess the environment was better on the inside. It was not possible to break the piece with your bare hands, although one of the two pieces made was slightly bent.

Has anyone understood the part about what kiln/furnace to use? Mark: you say that the kiln is a nitrogen-charged furnace? What about the "second hand vacuum furnace" that you mentioned in one of your earlier posts as distinct from the "kiln with computer"? Did you mean that it is only one owen needed, a nitrogen-powered vacuum furnace that is computer operated?

Mark: are you sure its all right to contact those you have worked with earlier? Has anyone here had any luck contacting them recently?

[mark pilato]

Hi all, its been along time since i posted on this topic, but I have some good news, I tracked down Rand German the man him self. He is excited in working with artists again on this, and he asked me to share his e-mail with you. so e-mail him tell him why you want it and see how you can be apart of this exciting process. Good luck, Rands E-mail german@cavs.msstate.edu
and all the best,
Mark

[mark pilato]

I changed the e-mail in the last post so make sure you got the right one.
all the best,
Mark
Randall M. German
CAVS Chair Professor of Mechanical Engineering
Director, Center for Advanced Vehicular Systems
Mississippi State University
P. O. Box 5405
Mississippi State, MS 39762-5404

email german@cavs.msstate.edu

[le granfred]

Hello

In France, when we wish to create a replica of a work of art, we mix bronze powder with a sturdy acrylic compound that we stamp in a rubber mold. When it is hard it is possible to think of different finishes such as patina. It looks just like a genuine bronze. But it is not as posh and valuable. To us it is junk.
Genuine bronze is matchless to true collectors, nevertheless, this new process is most interesting.

[mark pilato]

this is the real thing, its bronze not power mixed with acrylic, when its done chase it weld it patina it, the only difference is you get all the detail, and you cut out most of the steps. not snake oil. Step into the future read the thread.

[le granfred]

Ok

I went through this thread. And I see the interest of the process.
I wondering if it would not be possible to get the same result with a plasma torch projecting liquid bronze with high speed on the inner part of a ceramic mold just like paint. :confused:

you said: "With this process i could complete a chess set from the rubber mold to finished bronze in 3 days and give it to a scientist when I was done and he or she would say it's cast. how is that possible to take a three week process and shrink it down two three days."

my answer is that provided I have the original chess set, I bet I can do the same work in three or four days too, using traditionnal ceramic shell casting. It is very easy in fact. And with the original scale. I have my own way.

[mark pilato]

Thats cool, i have been casting work for over twenty years I had my own foundry and I'm some what of an expert when it comes to casting bronze in the lost wax process. let me know if I missed something, First you cast a wax from the rubber mold, if you are not going direct one of a kind, then you clean or sculpt the wax, then you sprue and gate the wax then you create a ceramic shell mold incasing the wax, then you burn out wax from the shell then you melt the bronze at the same time you heat the now empty ceramic shell, then when the bronze is at temp you pour bronze into mold that you have placed red hot on the pour floor or in the sand vats, then when cool,you brake out shell, bead blast or sand your preference, cut cups and vents off then you chase the bronze. well there is a lot more steps within these steps but thats it in a nut shell. As you and anyone who as ever cast bronze knows the casting is very rarely perfect, at the least you have positive to chase out and most of the time you are satisfied because its a dam good casting. okay with this process you poor the bronze plus binder into the rubber, clean it up, sculpt it , so nice, no skipping, chases like soft soap stone, sand it, use small detail tools, very clean edges. after you like your piece put it into the kiln in a can with powder around it, no shell no dry time no sprues no vents no brake out, then you set the computer and the next day its done, exactly the same as when you put it in but solid bronze. about five minutes to clean up and polish a little more if you want a mirror finish, weld it what ever same as a cast piece then a patina and your done. maybe it can be done as fast cast but you would be hustling, as for selling a sculpture that has been done in this process well i have sold work for 18,000 done this way and the collectors love the fact that its done in the pilato process. The reason I am sharing this process is because I know when it gets in the hands of some artists there will be no stopping it. its so fresh and so much more can be learned who knows what materials people will try using, who knows what idea's will come, and the coolest part its affordable so we will not have to brake the bank to cast our work. the pieces bellow were done this way they took about five minutes to chase after they came out of the kiln. the last one took 4 hours because of polish. anyway this was way to hard to write, good luck, and
all the best,
Mark

[le granfred]

Yes it is a wonderful process.
And it works wonders. :)
I wish I could use it in France as I think it is completely unheard of.
What is to be done to get it?
I am most interested.
Congratulations to an outstanding guy.
Look forward to learning more.
All the best
Fred

[Burkhard]

This is my first post on this board – apologies that it’s so long!

I came across this thread a couple of days ago and was interested because I tried to see if it was possible to make bronze PMC about a year ago (I was stunningly unsuccessful). Then got really excited that someone had solved the problems and even got it as far as a commercial venture – wow!. Followed by immediate disappointment that the company went out of business. But if one group of people can do it then it can be resurrected and if needs be, reinvented. I’m sort of hoping that there are enough interested people here that we can resurrect the technology between us. I’d love to say I’ve got the method to work and here’s how, but sorry no. Haven’t gotten further than re-commissioning my old kiln, ordering some bronze powder and doing some background reading and musing.

I’ve put some of this info down “on paper” for my own use, but in case people here are interested, I thought I’d post the stuff I’ve got so far. Excuse the style if it sounds stilted, too much like a lecture, and contains stuff others have already mentioned in this thread - I haven’t had time to edit it properly.

DISCLAIMER #1: Why do I think I can add anything to this thread? A long time ago (sometime last century) I got a PhD in chemistry and since then have been doing research in chemistry related fields for last 25 or so years (Sculpting for the last 15 years). However, I am NOT an expert in the sintering of metals or the process described by Mark Pilato so I make no guarantee that anything I say here is mistake-free. In fact, I can almost guarantee that I've made some mistakes.

DISCLAIMER #2: The following is a current “best guess” reverse engineering of what the “Pilato Method” entails. This is based on the comments that Mark made in this forum, the links to the “CISP Fall 2005” newsletter article that Mark supplied a link to and the patent (PCT WO99/54075 “Powdered material rapid production tooling method and objects produced therefrom” Inventors German, Weaver, Thomas, Atre, Griffo) which I think is the original patent referred to in the CISP article. However, this patent does not describe the actual “Pilato method”. As far as I could see the “Pilato method” has not been patented directly (and would be difficult to patent given the prior patenting art). I don’t claim that this is the actual method used or that anything described here will give the results that Mark described, or that it will actually work!

DISCLAIMER #3: As with any process there are inherent dangers and risk. Hence, I do not recommend that anyone tries to repeat these processes. In fact I recommend the opposite – that is, don’t try this. If you hurt yourself, blow yourself up, poison yourself, kill yourself, lose an eye or two, burn yourself or do yourself or your property some other damage, please do not blame me. You have been warned. Some safety issues to consider: Any work with hot objects, kilns, unknown materials at high temperature etc carries safety risks. Also, the “Pilato method” may produce toxic gases such as carbon monoxide. The “Pilato method” may produce flammable and/or explosive gas mixtures.

Background:
The Pilato method uses sintering of bronze particles to produce bronze objects. The method is potentially very useful because it simplifies the traditional, labor intensive, lost-wax bronze casting methods. Depending on how it’s used, it could also free the sculptor from limitations due to the necessity of having to produce moulds i.e. one could work directly in bronze. Does it work? It appeared to, as a company was set up and several customers (apart from Mark) had good experiences with the company. The company no longer exists, so the question is “can the method be reproduced in a non-industrial setting by ye average sculptor?”

Put very simply, in the Pilato method, an object (e.g. a sculpture) is produced using a mixture of wax containing 60-70% bronze powder. The object is then placed in a container and packed with 1-10 times its volume of a very fine powder such as aluminium oxide. The container is placed in a kiln that can be sealed and that has an inert gas (e.g. nitrogen) line inlet and an outlet attached. The temperature in the kiln is slowly raised. As the wax melts, the aluminium oxide absorbs the wax, as the temperature is raised further the wax decomposes. As the process is carried out in an inert gas (i.e. in the absence of oxygen) the wax does not burn in the kiln but decomposes to a mixture of hydrogen gas, carbon (i.e. soot), methane, ethane, propane, butane etc (similar to natural gas or LPG type gas). This flammable gas exits the kiln via the outlet line and is ignited here to prevent build up of flammable gas.

Please note: The mixture of flammable gas produced in combination with oxygen from the atmosphere and high heat from the kiln could lead to explosive gas mixtures. If the burning of the flammable gas mix is carried out in an oxygen poor environment toxic carbon monoxide could also be produced. A very (very) rough calculation says that a kilogram of wax could produce about 300 liters of flammable gas.

The temperature of the kiln is then raised to the sintering temperature of bronze (in article it said about 840C). After cooling, the object is removed from the aluminium oxide powder and is ready to be polished, patinaed etc.

In order for bronzes to be produced by a sintering method, three main problems needed to be solved. Firstly, sintering produces porous objects – how can one increase the density so that the strength, weight and feel of a bronze are obtained? Secondly, metal powders oxidize very rapidly at high temperature. If you heat bronze powder in air you’ll get copper oxide and tin oxide powder not a bronze statue. Thirdly, the bronze powder has to be mixed with a binder in order to form and mould it in its green state (i.e. in its pre-sintered state) – how can one remove the binder if we cannot burn it out in the presence of air/oxygen?

1. Sintering:
Sintering is a process that has been used to produce billions of objects that we use every day. It is mainly used for producing ceramics, everything from sinks to cups to bricks.

In the process, a material that is made up of very fine particles with a binder is formed into a suitable shape. In the case of clay, the binder is usually just water. The material is then heated to a point where the binder is removed and the surface of one particle fuses with the surface of another particle without actually melting.

As an analogy, imagine going into a freezer room and collect a bucket of ice cubes, about an inch wide, placed in bucket. Now take the bucket outside and allow the ice cubes to warm up just enough so that each ice cube has a thin film of water on the outside. Now place the bucket back inside the freezer and allow the thin film of water to freeze again – you have just sintered the ice. You could in principle invert the bucket and de-mould your ice-bucket object. If you did, you would immediately notice how many holes there are left between the ice cubes. This is a consequence of the sintering method – sintering gives porous materials.

There are two ways of getting around this:

Firstly, increase the temperature to as close to melting point as possible without actually melting the stuff. This is what one does with ceramics – the low-temperature, bisque firing leaves the pots very porous, with low mechanical strength, whereas firing to near the melting point of ceramics at 1300C gives hard, vitreous (glass-like) non-porous ceramics (or if you’ve pushed the temp too high it leaves you with a slumped mess). Down-side of this is that the higher the sintering temp the greater the overall shrinkage of the object. Too much shrinkage will result in distortion of the original object.

Secondly, use a mixture of particle sizes. For instance, if you take another bucket of ice cubes and mix in several handfuls of crushed ice, you can fill in most of the holes left between the large ice cubes. If you sinter the ice in this bucket, you’ll end up with a much denser object, fewer voids. The ratio of large to small particles is important in order to obtain maximum packing density but can be approximately calculated (I’ve got the numbers somewhere but haven’t looked it up at this stage) or can be gotten by experimentation.

The Pilato method makes use of the second point above in order to reduce the porosity to a low 13%. That is, one needs to use a mixture of particle sizes. The low porosity of 13% would make it difficult to tell a sintered bronze apart from a cast bronze just by looking at it and holding it. Presumably one could still use single-size bronze particles, but the resultant bronze would be far weaker than using a mixture.

(By the way, the statement in the CISP newsletter that a scientist would not be able to easily tell a cast and a sintered bronze apart is not true – just measure the density, the sintered bronze will be 13% less dense. Another by the way – using mixtures of particles in order to increase density is not something new invented by the Pilato method, this has been around for a very long time).

2. Sintering bronze – the problem of oxidation

Most people would have heard of PMC – Polymer Metal Clay. PMC comes either as silver PMC or gold PMC. PMC is vaguely similar to clay in its wet state. When dry one can simply heat it with a torch or in a kiln, burn out the binder and sinter it, and voila – a silver (or gold if you’re rich enough) object is created. If you’re a sculptor and have heard of PMC you immediately think “wouldn’t it be nice to have a few kg of this in bronze”.

Alas, life is not that simple. PMC is made up of fine particles of silver (or gold) in a polymer binder (methyl cellulose), with a few additives such as detergent to improve its handling ability, and certain amount of water. Gold and silver are part of a group of metals known as “noble” metals (other metals include platinum, palladium, iridium etc). Gold in particular doesn’t oxidize easily, whereas silver does oxidize but still much slower than metals such as copper, iron tin, etc. In fact silver is just inert enough to be used in PMC whereas copper oxidizes enough that it can’t be used. I had a look at the patents on the PMC stuff to see whether these guys thought they had a trick for doing copper, but couldn’t see anything (doesn’t mean it’s not out there somewhere – patents are deliberately obscure and difficult to read at times).

[Oxidation: reaction with oxygen to form an oxide e.g. iron plus oxygen equals iron oxide commonly known as rust. Air is approximately 21% oxygen, the rest is mainly nitrogen with small amounts of carbon dioxide and various other gases.]

The simple answer is of course to heat in an atmosphere of gas without oxygen e.g. in a nitrogen atmosphere, or even better nitrogen containing 10-20% hydrogen which will reduce any copper oxide back to copper metal. Using hydrogen can be done in the lab but is difficult for the average punter due to hydrogen’s high flammability and because it can form explosive gas mixtures at high temp if there’s a leak in your system and oxygen from the air seeps in. However, if the bronze particles aren’t too small and not too oxidized prior to sintering an inert atmosphere such as nitrogen or argon will suffice to keep the particles from oxidizing.

For the Pilato method this means that you need a kiln with an air-tight door and a steel tube nitrogen inlet going in one side of the kiln and an outlet at the other side of the kiln to let the nitrogen and any other gases produced during the heating out.

An alternative may be to place the object and the aluminium oxide into a separate steel container that has a nitrogen inlet and outlet. The container is then placed inside an ordinary kiln. This would mean that one doesn’t have to try and make a gas tight kiln.

For the average sculptor without access to nitrogen cylinders, gas fittings, tubing etc this may be the most challenging part to set up.

3. Removal of binder.

Speaking strictly from a patent point of view, the above two points aren’t particularly novel, the idea on how to remove the binder without burning it away in an oxygen atmosphere is/was the novel patent-able bit of the Pilato method.

However, this was already disclosed in the patent by German, Weaver, Thomas, Atre, Griffo in 1999, where they used the process to produce far more complex materials, consisting of a ceramic-metal, with a second infiltrated metal, than what is required for sculptures. In patent language this would mean that the Pilato method would be “obvious to those skilled in the art” after reading the original patent, but that the process isn’t actually covered by the patent. The good news is that, if there are no other patents out there, (but I didn’t look that hard), then this could mean that the Pilato process is not covered by a patent and hence available for exploitation/use by anyone.

Anyhow, back to the clever bit – how to get rid of the binder. What the Pilato process does is to use a melt-able material as the binder rather than a non-melting polymer and to pack a “wicking” powder around the object which adsorbs the molten binder. In the Pilato method the binder is simply wax. As the temp is raised the wax is soaked up by the wicking powder and then as the temperature is increased further the wax decomposes to a variety of gases such as hydrogen, methane, ethane, propane, butane etc (similar to natural gas) as well as soot. The decomposition occurs in the wicking powder, not in the bronze particle matrix, hence no problem with the soot contaminating the bronze powder and no chance of the bronze being damaged by internal gas build up. I think Mark Pilato mentioned in one of his posts that a flame is lit under the nitrogen gas outlet in order to safely burn off the decomposition gases.

The wicking powder mentioned in the Pilato method is alumina (aluminium oxide). However, the patent also mentions other ceramic powders can be used as long as the ceramic powder does not sinter at the highest firing temperature used. An important point is that the wicking powder must be fine enough so the wax preferentially is drawn into the wicking powder by capilliary forces i.e. the particles of the wicking powder should be smaller than the bronze particles.

Patent mentions that between 1 to 10 volumes of wicking powder to the volume of the bronze/wax is used.

Additionally, the binder also provides some mechanical stability to the object until the temp is raised to the sintering point. I.e. the wicking powder is packed around the bronze/wax object by “uniaxial tapping” to ensure intimate contact with the bronze/wax and to ensure maximum stability and support. I assume this means that one takes a stick and gently rams the powder around the object from above.


Other Stuff

The time of the firing i.e. wax melting, wax decomposition, metal sintering time is important, however, this will vary depending on the size of the bronze/wax being fired and will probably need to be fine-tuned by trial-and-error.

The foot-vibrator and the vacuum oven are probably used in the first phase where bronze/wax mixture is poured into the silicone mould. Given the amount of bronze powder used, the bronze/wax mixture probably has the consistency of concrete. In order to get a cast with minimal air pockets you ideally want to place the mould on a vibrating table inside the vacuum oven, fill the mould with the bronze/wax mixture and vibrate the whole thing under vacuum while the oven keeps the wax molten. This would give the best packed wax.

(I don’t know whether a foot vibrator would survive in the oven, so it may be easier to heat the mould, add the bronze/wax while vibrating, and then place in vacuum oven? Problem is that if there are any air-bubbles trapped in the bronze/wax you’ll end up with all the bronze/wax coating the inside of your oven as you apply the vacuum! Mmh, I suspect that you do need to stick the vibrator in the oven. Alternatively, the people who pour concrete often simply ram their concrete into moulds, live with imperfections or patch them after demoulding. Biggest danger is of course having a large air bubble trapped inside your bronze/wax object as you heat up the object while it’s still full of wax – could cause the object to crack or bits of it to explode. Once the wax is removed the bronze powder may be porous enough that trapped air can escape if the heating is carried out slowly enough.)

If I get any further I'll let people know.

[GlennT]

Thanks Burkhard for taking the time to so clearly explain the process. It allowed the "left brain" and "right brain" to catch up with each other long enough to get it!

[le granfred]

Yes, the idea itself is good.
But the process is not that good, and a well known technology could be operated to make the most of it. At least, this is my opinion. Think it over, it is rather easy I think. To be tried. ;)

[Burkhard]

Thanks Glenn, glad it made sense. The thing that really interests me about the technology is the potential freedom to create one-off bronze scultures without having to go through a mold-making stage. The potential time saving is also a big plus for me - I've set up my own backyard foundry for pouring bronzes, but am finding the amount of time it takes from sculpture, to silicon mold, to wax, to investment burn-out, to casting, to chasing.... to final bronze to be excrutiatingly slow for someone with my lack of patience.

le granfred - not sure I follow you - are you saying that the overall process could be simplified? I am hoping that this is true, but with these types of technologies sometimes it is easy to get a "result" but very difficult to get consistent, reliable, professional results. Hope I'm wrong. If you have ideas (or have tried things) please share - the "well known technology" you mention - are you thinking microwaves?

[le granfred]

Hello

I am wondering if the whole bronze clay work could not be fused in the middle of a coil. That would look very much like induction melting and instead of the melting pot containing bronze, you would have your wax mixture made sculpture.
see what I mean ?

more on this process here (http://www.azom.com/details.asp?ArticleID=1505#_The_Vacuum_Induction)

[Burkhard]

Hi le granfred
I have no personal experience with induction furnaces, so really have no idea whether it could work. Worth having a look in the literature though - I'll do a quick search tomorrow to see if anyone has published anything on sintering in induction furnaces.

Three potential problems: I don't know whether the temp control is good enough for the sintering to work rather than just melting the whole bronze. Also my understanding is that induction furnaces work by setting up a current in the metal to be molten - no idea whether the wax/bronze is electrically conductive enough for this to work. Also, I've heard that induction furnaces are very expensive to build or buy and probably way out of my budget.

But then again, as I said - I don't know what I'm talking about with regard to induction furnaces :) - it's always easy to come up with reasons why something won't work, only to be shown by someone who actually tried it that it can work.

[DanielUCM]

Nice to hear from you Mark and thanks for that detailed run-through of the process, Burkhard! Particularly for supplying a reason for why two owens might be used. That one has really been bugging me since I haven't found any reasons for it in the various sinter-related articles I have read so far. You also did a good job in explaining details about the functioning of the kiln for those of us without the relevant academic training. Have you thought about what kind of a kiln/furnace could be used for this? Sounds like it would be possible to manage without an industrial type sintering owen.

Regards
/Daniel

[Burkhard]

Hi Daniel - my current plan is to build a steel container with lid and gas lines that I can place inside my old pottery kiln. No way that I can afford a proper gas-tight furnace at this stage. Major danger that I worry about is decomposition gas leaking into the kiln and going boom if the container is not sealed properly. A gas fired kiln would probably be safer, but I'm not sure whether it's possible to get the accurate temp control that's required.

Ideally you would also want good temperature control on the kiln with the ability to program the temperature profile. This would make life a lot simpler as I suspect that one has to ramp up to 300-400C, then soak at that temp for a while (hour?), then ramp to sintering temp, 840C, and again hold for a while (again an hour or two?). Unfortunately all I have is a crude on/off control on my kiln and a pyrometer so I would have to nurse the firing manually.

[SPRINGFIELD]

I found this thread very exciting. I have also been experimenting with metal casting but my experience is very little. So I'm hoping that some of the more experienced can offer some pointers about my latest experiments.
I have also been trying to come up with a easy way to make metal sculptures and have tried what I believe is a original approache. One day I was thinking about how concrete is made. The sand is what makes the concrete strong the actual cement is just the binder. Without the sand cement is pritty week and has no abrasion resistance. So what if you took steel or bronze powder and bound it with powdered solder. The steel would add strength and the solder would bind it. Also because the solder melts at a low temperature you can have a steel or bronze strong sculpture at temperatures in the 450 f range. Considering how inexpensive steel is the most expensive part would be the solder which you may not need much of. I tried a small experiment with some steel filings and some solder filings mixed with some soldering flux and the result was a very hard strong glob of what looked to be steel. Attempts at larger mixtures didn't work so good. I think the problem is oxidation. Sure would like to here some comments from experienced foundrymen etc.

[DanielUCM]

Burkhard- That sounds like a clever way to go to start with the process. Are there some suitable steel-containers available that can be converted or would you have to construct your own? I guess one problem then would be to get it air-tight.
Springfield- You might want to check out liquid-phase sintering (spelling?) which I mentioned in an earlier post.

/Daniel

[Burkhard]

Daniel - my first thought was very low tech - a steel saucepan :) Cast iron would be better (less spalling) but difficult to get in Sydney at the moment.

Maybe a thin layer of bat wash or even plaster around the rim to provide a slightly better seal. Drill a hole in the lid for the tubing (either welded on or use tube fittings) and cross your fingers. I'm hoping that with the densely packed wicking powder there wouldn't be a lot of space for air in the can anyway and one may be able to get away with this setup. It's worth a try before going to more expensive options.

I just got my bronze powder and wax and made some test ingots. Highest loading I could get was 33g bronze powder and 3.5g wax (higher quantities of the bronze (64% wt/wt) resulted in a more powdery feeling solid, but still very hard and could be suitable for carving). Behaviour of this stuff is very similar to a corn starch and water mixture i.e. when agitated quickly it is a stiff paste but is fluid when allowed to settle slowly and vibrated. A vacuum oven and vibration table would definately be useful for getting air out of the mix and getting good quality mold castings. (Alternatively an ultrasound baths may be useful for densification/deaeration of the hot wax/bronze mixture into the molds.) If the gods (or at least a reasonable percentage of them) are willing I hope to do a test firing over the weekend.

Springfield - I have no expertise in this, but the liquid phase sintering process that Daniel mentioned might give you some pointers. In terms of the amount of solder - when mixing two powders you need at least 16 % (by volume I think) to reach the percolation threshold (i.e. the point where the solder, in this case, can form at least one meandering but complete path from one end of the material to the other). Btw, it's also possible to buy tin powder and maybe mix this with the steel or bronze? I suspect that the main problem will still be oxidation (same as for the sintered bronze process) as well as dimensional stability - in the case of solder, if you're actually melting one component then this would make the whole structure fairly fragile while the solder is in its molten state. Sorry - rambling, I actually have no idea!

[SPRINGFIELD]

Thanks Burkhard and DanielUCM for your info. You guys sure have a lot of info and experience. Sounds like I better get some more experience using traditional methods for a while. I experiment so much I never get anything finished. Right now I'm experimenting with making shell molds using different materials for the shell.
I looked up Liquid Phase Sintering on the internet and got lots of info. I hope to give it another try in the future. I noticed that E-Bay has a lot of Vacume Ovens for sale and some are pritty inexpensive. Thanks again fore all the advice.

[sgriff]

Hey Burk... as i was reading your info on the texture of the bronze/binder mixture you are experimenting with i reviewed the info that mark gave in his on of his first posts..about adding Empoline...maybe this enhances the texture and workability of the "clay". I couldnt find it online but i did find info on ceramic additives/plasticizers that burn out.
I have 2 skutt kilns sleeping in my studio..i think this process has given them new legs..

[Burkhard]

Hi sgriff - yeah, I was starting to wonder what the heck empoline was as well. Also haven't been able to find any info on it at all. Mark said that it's only there at 2%, which indicates that it must have a real function, (else at such low conc why bother including it). Does anyone have any ideas what empoline is/could be? (may not be the correct spelling)

With regard to other additives/plasticisers - remember, in principle in this process they have to melt, wick into the surrounding alumina powder and then they have to decompose rather than burn out (no oxygen), so polymer additives may not work - don't know. Wonder whether the stuff they put into Sculpey (I think it's dibutyl or dioctyl phthalate) would work. The phthalate volatilises at 130C and could be removed without decomposition. Of course any frogs in the area would probably start to grow 5 legs and two heads, but this doesn't seem to worry Sculpey users.

[DanielUCM]

I can just second to that - I haven't found any info on the epoline or empoline, last time I searched was however at least six months ago. There is some other binder I've read about, but it might just be inappropriate for our purposes, I'll see if I find the name of it.

It will be great to hear how your tests work out Burkhard! I've been saving to invest in some more advanced equipment than what I currently make do with, and if your low-cost method works - excellent. Unfortunately I'll leave Sweden for a few days soon, so I hope I get to know about your results before I leave :) I will upload a picture of the result of one of my extremely low-tech experiments, just for fun, so you know the baseline of what you must accomplish!

Springfield, I think its great that you experiment a lot, but as you say it is good to get a somewhat solid base in some established method first - if nothing else it makes it easier to read through more advanced articles.

Has anyone picked up on Marks suggestion and e-mailed the researcher he suggest that we contact? Maybe he can give some pointers on the E(m)poline if we would really get stuck?

[Burkhard]

For those interested – my first experiments in trying to recreate, at home, the sintered bronze process described by Mark Pilato. As is usual with this type of experiment it worked just well enough to make me want to continue – no champagne to celebrate yet (but worthy of a couple of beers).

Usual caveat: Because I do not know who may read this, the following is provided for information only. I do not suggest that anything I describe here is safe or should be attempted by anyone who does not have the appropriate training. Please see safety warnings on my previous post. If you injure yourself or others, don’t blame me – you have been warned.

The question I wanted to answer with the current trial was whether it’s possible to create an oxygen-reduced atmosphere in which to fire the bronze/wax mixture that would enable sintering without severe bronze oxidation occurring. Main interest for me is also whether it’s possible to do this using stuff that’s readily available to most sculptors, or whether this really is a technology that needs to be done using fairly expensive industrial scale technology (kilns, temp controllers, nitrogen lines etc).

I prepared seven samples, to play with the bronze/wax ratios etc:

Sample A: 3.5 g microcrystalline wax + 54 g bronze powder (94% w/w, 64% v/v). When hot, very dry looking, powdery mixture, pressed into mould while hot. When cold was firm solid but powdery.
Sample B: 3.5 g microcrystalline wax + 30 g bronze powder (90% w/w, 50% v/v). When hot was a very viscous paste, behaved similar to cornstarch/water. Bronze settles in mould with vibration and a 2mm layer of wax formed on surface.
Sample C: 3.5 g microcrystalline wax + 40 g bronze powder (92% w/w, 57% v/v). When hot, dry powdery mixture similar to A.
Sample D: 3.5 g microcrystalline wax + 34 g bronze powder (91% w/w, 53% v/v). Similar to sample B except only very thin layer of wax left on top of mould.
Sample E: 3.5 g jewellery wax + 33 g bronze powder (90.4% w/w, 52% v/v). Settles in mould similar to sample D.
Sample F: 3.5 g jewellery wax + 3g tin powder + 30 g bronze powder.
Sample H: Same as sample E.

Samples cast as round buttons ~ 3cm diameter, 1 cm height.

My steel container + kiln was prepared as follows:

A hole was drilled into the lid of a stainless steel cook pot (not aluminium, anodised aluminium, or stainless with aluminium base!) and ¼ inch stainless steel tubing was attached using Swagelock fittings. The tube was long enough to protrude out of the spy-hole at the side of the kiln. No nitrogen inlet was provided for this experiment.

A layer of fine TiO2 powder (used rather than alumina simply because it was on-hand) was packed into the pot, the samples were placed on top and the pot was then filled with further TiO2 powder until the pot was nearly full (about 3/4 inch head space left). The powder was tamped down with the end of a piece of wood. The lid was placed on the pot and the rim was sealed with a small amount of plaster of paris mixture (this later cracked severely while firing, but still held the lid firmly in place – although probably not air-tight). Pot was assembled into kiln, the pyrometer ended up sitting just above the lid of the pot.

(As a control, sample H was packed in the TiO2 powder in an open steel dish i.e. exposed directly to the kiln atmosphere.)

A small LPG gas torch was placed so that the end of the stainless steel tubing protruding from the kiln sat in the middle of the flame of the gas torch (this served a dual function, firstly it ensured that any decomposition gas generated from the wax would be safely burned off, and secondly it ensured that no oxygen could back diffuse into the tubing and into the pot).

Kiln was started and heating rate adjusted manually by controlling the on/off time. Initial heating at 70% on rate raised the temp to ~ 570C within 80 minutes, when a small flame appeared from the end of the steel tube. Heating rate was reduced to 55% for a further 60 minutes until there was no more flame coming from the steel tube (temp had risen slowly to 634C during this time). Note the flame was extremely sooty even when the gas torch was turned on full with an oxidising atmosphere – danger of inhalation of toxic materials, including carbon monoxide poisoning. Good ventilation essential. Heating was increased until temp reached 850C and by adjusting the on/off time the temp was maintained between 843 and 850C for a further 120 minutes. Kiln was shut down, lid lifted soon after to rapidly cool everything. After 20 min the gas torch was also extinguished.

Results:
Only partially worked – most samples not fully sintered. I think the main problem was that I measured temp at top of pot, not inside or bottom. I found that in my kiln there was a largish temp gradient between top and bottom of kiln of ~ 80C, hence the temp inside probably never got to the 840C required.

Sample A: bronze powder, no structure. Not sintered at all. 100% powder
Sample B: Looked solid, but attacking with screwdriver revealed the outside was 2 mm sintered, nice bronze coloured looking metal, can be filed, polished, kept its shape (including the sample letter scratched into the surface). Inside – still lots of unsintered powder. ~70% powder
Sample C: some sintering i.e. hard outside crust. ~ 90% powder
Sample D: Looked solid, as per sample B, but only about a 1mm sintered outside layer, the rest still powder. ~80% powder.
Sample E: powder, no sintered structure, ~100% powder
Sample F: Very thin layer of sintered skin, ~ 97% powder
Sample H: (this was the one exposed to kiln atmosphere) outside was a ~1mm thick skin of what looked like black copper oxide (+ tin oxide?). This could be pealed off reasonably easily (although it was quite hard and had retained good imprint of the letter scratched into it). Inside was red copper coloured hard, metallic material. I suspect the tin had oxidised severely and left the chunk of copper behind.

Preliminary Conclusions:
1) Major problem seemed to be that the bronze powder did not sinter completely.
- probably pyrometer readings were low compared to the actual temp inside the pot.
- probably need to soak the pot at sintering temp for longer.
- could be a major problem if the kiln temp is not uniform within the kiln i.e. the top of a sculpture could get fried whereas the bottom is not sintered properly.
2) The bronze/wax mixture if fired in air oxidises heavily to the point where its not useable even when packed in a wicking powder such as TiO2 (sample H).
3) The present system seems OK with regard to producing a non-oxidising atmosphere inside the pot, but this needs to be confirmed (i.e. is it good enough for the longer sinter times and higher temps that I might need to fully sinter the pieces).

Less important findings:
4) For some reason not all waxes are equal i.e. jewellery wax (the type used to make small rings etc for lost wax casting) did not yield significant sintering. May need to increase temp further? Or may be a function of wax. Why? - don’t really have the foggiest idea. Maybe the jewellery wax expands too much prior to melting, moving the bronze particles too far apart for easy sintering.
5) Also, for some reason the sample with the lowest amount of bronze powder (sample B) gave the best sintered sample. I would have expected the sample with the highest bronze loading (sample A) to be the best sintered, however this was just dust. Why? – again not the foggiest, but may have something to do with the packing of the bronze powder in the mould prior to the wax cooling?
6) Addition of 10% extra tin powder didn’t do anything exciting at this stage.
7) Not having an electronic temp controller that one can program is a nuisance, but nursing the kiln to manually adjust the temp is do-able.

Next steps:
=> repeat experiment but with increased temp and soak times to see if the problem really is to do with the sintering temp not being reached.
=> have another beer.

[GlennT]

Some further analysis;

The level of intoxication produced by the beer divided by the square root of confusion plus or minus the ponder and muse factor may hinder the sinter in the ratio of (94% xy ) ( 760g key lime pie R squared ) where x = the nosy neighbor next door and y = studio vermin in rural locations.

Hope that helps :D

[mark pilato]

hi Burhard call me, I think i can help you get over some of the humps.
607-326-3508
all the best,
Mark

[RWJR]

looks like these guys have it figured out http://www.powdermetallurgyco.com (http://)

[Burkhard]

Hi Glenn - I like it! I think the equation may also be applicable to the rest of my confused life. Yeah, I know, I do tend to get overly analytical and detailed when I'm in technology-nerd mode :D One of the reasons I love sculpting - totally different parts of the brain used.

Hi Mark - thanks for your generous offer, however, I'm sitting in Sydney Australia so email may be simpler (I think you're 15 hours behind time-wise? I'll have to check). If you have the time to post any comments, suggestions, glaring errors etc about what I've done so far that would be cool (I know you're busy). I think the way you described the process in your earlier posts really got a lot of people exited (just look at the number of hits this thread keeps getting!).

[Burkhard]

Hi RWJR, yes, this is the sort of "industry standard" process that's actually been around for quite a long time. Sintered bronze parts are often used as self-lubricating parts because the porous bronze can be impregnated with oil. BUT the processes used in industry usually involve high-pressure compaction of the powder into steel moulds prior to sintering. There is quite a large industry using sintered metal powders to produce all sorts of objects - it's especially interesting for producing objects from metals that have very high melting points. However, these methods aren't really applicable for sculpture in general unless you want to mass produce your work.

[Burkhard]

The following is pretty much an excercise in learning how to post picture on this forum - obviously too much time on my hands. Hope it works, if this keeps going I may just get my act together enough (scary) to post some pics of my sculptures as well.

The first picture is inside of the kiln with my high tech cooking pot showing steel tube exiting kiln. Pic 2 showing outside of kiln, pyrometer and gas burner positioned at exit of steel tube. Pic 3 amount of flame produced at mouth of steel tube from decomposition gas from the wax. Pic 4 same thing but with burner back in place. Pic 5 shows 3 samples: left, sample B, the sintered piece that pretty much worked; middle, the way most pieces looked i.e. not cooked all the way through but with a sintered skin; right, is the piece (sample H) that was sintered just in air showing lots of black oxide and copper red inside.

http://i154.photobucket.com/albums/s280/Burkhard_photos/KilnA.jpg http://i154.photobucket.com/albums/s280/Burkhard_photos/KilnB.jpg http://i154.photobucket.com/albums/s280/Burkhard_photos/FlameA.jpg http://i154.photobucket.com/albums/s280/Burkhard_photos/FlameB.jpghttp://i154.photobucket.com/albums/s280/Burkhard_photos/SamplesB.jpg

[Burkhard]

Aha, the mysterious epolene

Epolene: The toughness, opacity, and gloss in high-quality candles has traditionally been determined by the quality of wax used. The high-melting-point petroleum waxes that provide these desirable features have become scarce as the market for high-quality candles has grown. This has generated a need for additives for low-melting-point waxes that will impart the desirable features normally associated with the more expensive, higher-melting-point products. Eastman Chemical Company offers polyethylene waxes that can fill this need, including Epolene N-34, Epolene N-10, Epolene N-11, Epolene C-15, and Epolene C-10

http://www.quimisor.com.mx/tecnicas/Epolene%20Waxes%20as%20Candle%20Additives.htm

[DanielUCM]

Burkhard, thank you for your thorough reporting! Encouraging that you managed to avoid oxidation with that accessable solution.

For those interested I have here attached a picture from an experiment (well mayby not experiments in the strict sense of the word..) that I did around August last year. I did two samples using bronze powder of a 89/11% mix of Cu and Sn. With a "fraktion" (I believe that's the word my supplier used, can't recall what term is commonly used in English) of <0,045. I used two different forms of mikrovax/microwax supplied by a Swedish company. I unfortunately didn't have time to record my endevour in any serious manner since I had some eight other samples (not relevant to discuss right now) that I wanted to process during the same time-period over a weekend (the owen I use is not located where I live most of the time so I seldom have time to use it). I just did a couple of blobs of the mix based on the two different forms of wax, the texture was more smooth than powdery, if that's some indicator of the ratio :) I used an open container so I naturally got the problem with oxidation.
Why I tell you guys this is because I did the sintering at a higher temperature than you Burkhard, most likely over 850 celsius (judging by the colour of the stainless steel container I would like to think it was about 900 celsius), and got a solid core. I baked it for some 1,5 hours at that temperature. The attached piece is about 50*40 mm with a thickness (around the place of where I have filed away some of the outer layer) of about 3 mm. The core of solid bronze is around 1,5 mm thick. Note that the so called core does have a surface riddled with tiny holes. It seems like the aluminum oxide powder and the outer layer of bronze powder protected the inner parts enough for them to sinter. The piece is hard enough that it cannot be broken with the hands (the other piece I was able to bend though). I used a gas-powered owen.
Next time I do this I'll try to keep better records (and use better equipment), but at the point of the test I just wanted to get started.

And the epoline mystery is unravelling, nice!

/Daniel

[mark pilato]

okay guys as far as the mix- its easy, get a crock pot turn it to about 350 pour in the wax,let melt, then pour in your bronze powder making sure the powder has a range in granule size, like a stone wall. mix it like plaster until islands form. when the batch is up to temp, 350, then vibrate the pot with a foot massager or vibrating massager. skim the wax off the surface after about two minutes, then pour mix into the mold making sure to also vibrate mold at same time. It helps to have a large pour cup because the bronze will also settle leaving a wax layer on top. If you have a vacuum furnace this works the best, put the rubber mold in and pump out the air. I bought one second hand for 50.00. after this is done wait for it to cool, clean it up, sculpt it, making nice then put it in a small steal can surrounded by aluminum oxide powder . first put about an inch of powder at bottom of can, then place piece in can, so that it has an inch of space around it. then pour in powder, after its full tap the can up and down, this helps pack the powder. If you are doing relief sculpture or small pieces all you need to do is pour about a 1/8 inch powder on a kiln shelf then place your sculptures on top and cover with the powder. Ive done about 100 small sculptures in one run this way. okay heres the next step the kiln, picture below. place cans in stainless can that is in your kiln, put lid on, turn on nitrogen bring your kiln temp up to about 350 c for your first hold until wax is burnt out then bring to second hold of about 550 c for about an hour or if you have a full kiln 3, then bring to sintering temp, hold for two hours turn off gas and kiln and let cool. you must use nitrogen or this wont work. picture bellow shows kiln with stainless can inside, I used the kilns port holes to plum in stainless pipe welding it to can, one pipe is for burn out, one pipe is for pyrometer and the other is for nitrogen. the top of the Stainless can does not have to seal, the nitrogen does the trick. you can place kiln shelves in you main can the the smaller cans can be placed on kiln shelves making sure there is 3 inches of space between. hope this helps. hope you ge it,
all the best ,
Mark

[DanielUCM]

Thanks Mark for that additional information about the Pilato-process! So you have one larger container which is permanently inserted in your kiln and then you can just place whatever other cans you have filled in that.. And you don't have to seal the larger container. Concerning the three pipes: Do they need to be placed in some specific order to make sure that the nitrogen does its work, and that the burn out functions properly?

(Everyone who starts utilising the process for themselves according to your instructions should send you paper copies of photos of their first work using it - so you can get an archive of what the process have been used for!)

/Daniel

Sorry, I just saw that your attached picture, opens up for a bigger view with more detail on the ordering of the tubes!

[mark pilato]

What we did was place cans in a circle on our kiln shelves, very much the same way if you were firing clay. we put the pyrometer cable in the powder in the can that was the farthest away from the kiln elements and hooked it up to a computer so we could see exactly what was happening making sure that sculptures were not getting to hot, also very important. You dont want to melt the bronze you just want it to fuze together. the separate cans that are in the kiln do not need tops, after the powder sucks out the wax and you vamp heat up to second hold to burn out, the wax can freely escape out your burn out tube, which by the way should have an after burner/ flame to burn the wax as it comes out to reduce emissions in the air. the bigger can or your reduction container just needs a tight fitting top, no seal. We bought ours from a company that makes stainless cans. the nitrogen creates the perfect atmosphere in all parts of the can. I have some tricks of the trade i will share later when your ready to slush cast.
all the best,
Mark

[Burkhard]

Thanks Mark for the additional info - much appreciated. Can't wait to have another go!

[mark pilato]

Hi all,
I have been getting a bunch of phone calls/emails on this, sorry if i have not returned them, i am overwhelmed with sculpture projects/family at the moment, I still have not reset up in my studio but I am considering starting it up again, along with a small scale foundry for my larger works. I will keep you posted, has anyone had any luck with Rand German?
All the best,
Mark

[Burkhard]

Direct bronze: came across an interesting patent the other day that people may be interested in: US 4854970 (just google "US 4854970" and you'll find it). Basically describes a metal clay made from 95% metal powder (nickel in the actual case of the patent) held together with 5% bentonite. Mix, add water, voila - metal clay. Apparently the inventor, R. Wiech, died a week before the patent was granted.

Had a go using bronze powder - gave a fairly "brittle" clay, sort of like a short pastry dough (for those who cook). Sintering at 900C for 2 hours under inert atmosphere gave a reasonable result for a first trial (see attached pic, height about 5"). Probably dried the bronze clay too quickly, hence some cracks appeared. Also, ignore the colour - I tried a quick patina but ran out of time to do anything properly. The material apears to be solid metal all the way through (I cut through a small sample block that I fired at the same time - beautiful bronze colour, could be readily polished to a mirror finish).


http://i154.photobucket.com/albums/s280/Burkhard_photos/Direct%20Bronze/Picture1.jpg

[dawn]

Well, now it seems simple enough for dummies like me. But...what is an "inert atmosphere"? :o

[Burkhard]

Dawn - apologies for the jargon. If people are interested I'll post a more complete description of what I did as soon as I have a bit of time.

In brief, an inert atmosphere means firing the bronze clay in an atmosphere of either argon (slightly expensive), nitrogen or possibly carbon dioxide (I haven't tried this one yet). If the bronze clay is fired in air then all you'll end up with is a lot of annoying brown copper oxide powder rather than a sintered sculpture. Using the bronze clay rather than the "pilato method" has advantages in terms of much shorter firing time (3 hours total), no noxious gas evolution, and ability to directly produce a sculpture from the bronze clay. Drawback is still that you have to fire in the absence of oxygen just like the Pilato method (I'm currently trying to figure out a way to do the firing directly in air, and although I have some ideas it's slow progress). At the moment I've got a large steel pot sitting inside the kiln with a 1/4" steel gas pipe feeding argon gas (ex welding supply company) into the pot. The lid is not gas tight so I don't need an exit line. The sculpture goes inside the pot, gas flow is turned on a little bit and the whole kiln is heated to 900C. Ceramicist know of this type of arrangement as using a saggar, although usually the saggar is made from ceramic not metal. It may be possible to fire the clay in a gas kiln under very heavy reduction atomsphere without the need for a nitrogen atmosphere - haven't tried this yet.

SAFETY NOTE: If you're using a metal pot with an electric kiln make sure that you cut off any protrusions such as handles etc. I believe that the heating elements inside a kiln are "live" when it's turned on i.e. 240V. If the metal pot touches the elements and you touch the pot or the metal gas line you could electrocute yourself. I also put some kiln stilts around the outside of the pot so that if I knock the kiln then the pot cannot fall onto the elements.

Also a lot of (cheaper) cooking pots have bonded aluminium bases (i.e. aluminium core inside a steel clad base) - these need to be removed (angle grinder, heat) otherwise the Al will melt during the firing. At best this will result in a mess in the kiln, at worst a small explosion inside the kiln as the pot ruptures.

[dawn]

Whoops! I was wrong.

Are these somthing commonly practised by ceramists, I mean, the setting up of this kind of kiln? If so, maybe I could ask some of my ceramic friends to help me with it.

[DanielUCM]

Burkhard - Thank you for giving us some of the results of your research! It's appreciated. In a couple of weeks I'm going to get more time on my hands and then it will be great to try this out. I'll read the material you suggested but I just have to ask you a couple of things: Do you just let the clay dry in your mold enough so it holds up to be moved to the kiln? Do you still need to use the aluminium oxide to stabilise the green bronze?

Best wishes
Daniel

[Burkhard]

Dawn – finding a potter who is also a welder (!) would probably be your best bet in terms of setting up the kiln and helping you find a supplier of gas cylinders, valves, tubing etc. I’m a lousy welder so I used a thingamajig called a “stainless steel Swagelock bulkhead union for ¼” tube” (Part No.: SS-400-61 from Swagelock.com, bought over the net for about $25) to connect the tube to my pot. This just requires you to drill a hole in the pot and then using two pliers one can connect the tubing. They also sell steel tubing but only in 6m lengths (for about $40 I think).

If you do try and set this up you should also get such a person to cast a critical eye over the set-up in terms of safety i.e. is the cylinder properly secured to a wall so it can’t fall over, is the ventilation adequate so that the kiln firing isn’t going to poison you but also that the nitrogen gas isn’t going to asphyxiate you, what happens if you bump into your kiln – any chance of the pot contacting the kiln elements and becoming live etc etc. I think I’m getting old and finally getting cautious - too many near misses due to my own stupidity.

Daniel – the two materials (i.e. the bronze wax from the Pilato/German work and the bronze clay from the Wiech work) behave very differently.

The bronze wax can be poured into silicon moulds and is quite hard when it cools. It can be readily carved but isn’t really suitable for additive modelling type of work as far as I can tell. Maybe there’s a trick to this but I haven’t found it so far. Also, I haven’t actually been able to get the bronze wax method to work satisfactorily for me so far. I suspect that filling the silicone mould while vibrating it is quite important, there are whole books written about “vibratory compaction of metal powders” for producing sintered objects.

The bronze clay acts like a very “brittle” clay and just like clay it’s difficult to use in silicone moulds. The little figure in my previous post was done by pressing it into a two-part silicone mould, carefully taking one half away, allowing the bronze clay to dry for a day, demoulding fully and then refinishing it, filling in cracks etc before allowing it to fully dry. Overall it was not that successful, some distortion and fine detail would be difficult to transfer. I think part of the reason the final figure had cracks in it was due to the uneven drying. A plaster press mould would probably work better, might even be able to slip cast this stuff – don’t know. The clay will probably be better suited to direct modelling type of work. I’m currently trying to do a couple of simple figures by direct modelling. One might also be able to make larger blocks in a plaster mould, allow to dry and then to carve the stuff.

I tried to get clever and make a bronze clay with better modelling properties by adding methyl cellulose binder and olive oil to improve handling – could improve the modelling properties of the clay but on firing all I got was powder. I suspect that the drying process of the bronze clay also serves to shrink and hence compact the bronze particles. This compaction seems to be important.

Be warned the stuff is very messy. I have no idea how toxic copper is when used in this way i.e. how much could absorb through the skin. In principle you should wear gloves. Also, although copper is not that toxic (you need to swallow about 20-30g of ionic copper to kill an adult) make sure you don’t leave any around where a child could swallow some – the copper would dissolve in the acid of the stomach and a teaspoon of copper clay could poison a child.

When I fired the bronze clay, I did pack it in some TiO2 powder that I had. This was mainly for support, but is not required as in the bronze wax process to wick away any wax. Next time I’ll try some ordinary builder’s sand for support, I suspect that it would work just as well.

[dawn]

Thanks. I'll try to ask around. I wish there will be a step-by step- book on this whole process someday.

[Burkhard]

Working on it Dawn :) Problem is that at the moment it's still the blind leading the blind. Well, perhaps we've managed to get to the "partially sighted" stage.

[DanielUCM]

Thanks! Yes, these types of formulas have different strenghts and weaknesses so I guess that so far the choice depends on the particular sculpture one wants to do.

(Burkhard - pm sent)

/Daniel

[mahmoud haggag]

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[jphariot]

Hello Burkhard,
I am really impressed with the amount of research you have done here.
I was doing a google search for Bronze Clay and lucky me. I have been researching this on the side for about 3 years now. I am impressed with Marks process, and especially his work. But when you described the Gasses emitted during the wax burn out, I got a little nervous. But I would still prefer that to investment casting hell.
Let me mention that I have been investment casting on and off for about 5 years and hate every bit of it.But now I have no choice, because I have some projects that require it. So I have been looking at the PMC for about 4 years.
Wondered about using it for Bronze and other alloys, but realized that they would oxidize unless placed in an inert atmosphere.
I have a question: Would it work to place an electric kiln into a vacuum chamber? Wouldnt that make it inert? If I have to use Nitrogen then I will. But I would like to get a clearer picture of how that works?
So to continue, I was a bit nervous with the gasses emmited and wondered why not just use the same binder as the PMC?
Then I read your discovery of the Bentonite formula. Sounds good. I think I have used Bentonite as a sand casting binder??
At any rate, how is the process going now? I was planning to start my experiments by late summer-early fall, but I am really getting so tired of investment casting that I think I am going to push it to a sooner date.
I am working on building a resin casting machine, and I am developing my own alloys, so I am really into helping you all here in working on this.
I am wondering if Mark is very commited to the Wax-Bronze Powder system, or if he is interested in helping with some other methods? I am just trying to find an efficient, consistant, and safe system to sinter Bronze and other alloys.
I currently cast a lot of pewter into silicon. Love the undercuts and freedom. But the choice of alloys is really limited. Its left me with the dreaded investment casting.
Thanks again, and please let me know where your at with the Bentonite Formula?
Thanks Again,
John Hariot

[Burkhard]

John - thanks, last summer I got as far as setting up a small foundry and learning how to do small lost wax pieces and also very quickly got tired of the amount of work and effort required.

In terms of vacuum chamber - in principle yes you could set up the furnace inside a vac chamber, I think I have seen reports where this is done. However, you'd need an impressively large vac chamber to stick a whole kiln inside. You'd also need to provide access for power and control wiring and I'm guessing a very good quality oil pump. Alternatively sticking a vac chamber inside the kiln could be done, but now you need to make sure that the chamber is vac tight at 900C and isn't going to implode at these temps. Also if using a vac pump remember you'll need very good gas traps else the soot produced will quickly gum up the vac pump. If you have access to such equipment it's possible, but not worth considering to do at "home" because it would be much simpler to just connect a gas line to the chamber and flood the chamber with an inert gas. I haven't gotten around to taking pics of my current setup yet - it's our end of financial year coming up and I'm up to my ears in project planning, budgets and other $%#* stuff.

I just finished a "quick and dirty" experiment that shows that carbon dioxide gas can also be used as the inert gas. This is useful because the easiest (and probably cheapest) source of gas cylinder/inert gas combo for me are CO2 gas cylinders from the guys who supply the beer home brew crowd (apparently used to charge kegs of home brew). Maybe I can kill two birds with one stone.

Yes, you probably did use bentonite as a sand casting binder. Should also be available at most pottery supply shops as it's used in clay and glaze formulation.

I've now fired the bronze powder/bentonite (95:5 weight/weight) mix three times, all more or less successfully. My current firing regime is to load the pieces inside a can packed in TiO2 (for support) inside a 14l stockpot, place lid (lid has steel gas line attached that is connected to gas cylinder) on top, place three heavy steel weights ontop of lid (to give a reasonable seal), turn on gas. I then ramp up the heat to 900C, which takes me two hours, then hold at 900C for 1.5 hours, turn the kiln off, and allow to cool under inert gas. So far I've not been very patient, so after 30 minutes I open the pot up (wearing welding gloves, face shield and using raku tongs) and take out the bronze pieces and quench in water to see the results. I probably should let things cool down far more, the bronzes are still red hot at that stage.

Couple of things I've noticed with the bronze clay:

One - with the pieces I've done so far it looks like the very top of the surface (top 0.1 mm?) of the fired bronze clay is quite porous and pitted (using a magnifying glass) and in order to get a good finish I need to run a buffing/sanding wheel over the surface. This is not really a major problem except for very fine detail. Don't know whether this is intrinsic to the bronze clay, the firing temp inside my pot, or the size distribution of my bronze powder.

Two - my larger hand formed pieces develop cracks in them either on drying or during the firing. This may be due to bits of bronze clay not bonding when I add them together in the "wet" stage. I've tried adding some paper pulp to the bronze powder/bentonite mix (approx 1-5 g paper/100 g bronze powder/bentonite) in order to make a "bronze paper clay" and this fired as well as the ordinary bronze clay. I think it may be better to sculpt with (not as "brittle"), and I'm hoping that just like ordinary paper clay that it will allow the joining of wet clay pieces more successfully.

[I'm going to try to go back to the bronze wax soon to see if I also see the surface pitting there, but it really does produce a whole lot more soot and noxious gases than the bronze clay. (At one stage I lifted the lid of my kiln up during the firing of a bronze wax. My steel pot lid must have leaked quite badly because the inside of the kiln was full of flammable gas which gave a quite exciting whoompa as the air hit the gas and ignited in a ball of flame. Luckily I was wearing face shield and long sleeved welding gloves so no harm done. Very pretty really). Also, I've not yet managed to figure out a 100% effective way of burning all the soot that comes out of the gas outlet line when using the bronze wax, even sticking a propane torch on the outlet was not totally effective.]

In terms of why not use the same binder as used in PMC ? Good question - simply because I've been totally unsuccessful with this so far - I'd love to know why. It could be due to a whole bunch of reasons to do with the way I fired the pieces, or with the fact that the particular binders I used where slightly different and decomposed leaving too much residue behind or something else. This does not mean it won't work, I just haven't hit on the right combo. Too many things to try, alas, not enough time.

[enitharmon]

I have been reading the progress here for months now, quite inspiring. Always exciting when things go boom! Motivated me to read patents and articles. Burkhard, good to see Aussie initiative! the patent for the bentonite mix suggested using an organic substance for greater viscosity...sugar was mentioned. Did you try that? Experience with ceramics, joining pieces to avoid cracks...if you cross hatch and slip the join, blend the join and the seal the sculpture in a plastic bag leaving it for a few days to redistribute the moisture across the join has been successful..might work with the bentonite mix. An article looking at the oxidation, weathering and porosity of the sintered bronze written by Dr German sounds promising too and shows [microscopic] images of the process.

[Burkhard]

Hi enitharmon - thanks for the encouragement to all the people who posted in this thread. Hopefully slowly but surely some more people will have results (positive and negative) to share. :)

I haven't tried the sugar additive (I thought he used that to increase the amount of microorganism in order to increase slipperyness. I'll have to reread the patent. I sort of assumed this was just one of those throw away lines used in patents as I don't think it was actually listed as one of the patent claims, but you're right - worth a quick experiment).

With regard to the joining of pieces of bronze clay - I sort of tried cross-hatching (although not as well as I could have), adding bronze clay "slip" to the parts before joining, and also left the small figure in a plastic bag for a couple of days to equilibrate the moisture, followed by slow evaporation in the plastic bag with only a few holes, before removing the bag etc. No joy. Cracks still formed. However, this may still be just a matter of technique. Read in another article that in order to avoid cracking of ceramic greenware, they did the initial drying of their green body at 90% humidity for 24 hours when most of the shrinkage occured, followed by normal drying.

[enitharmon]

Hmm if the bronze paper clay works whole areas of possibility are opened, modelling, shaping, carving, embossing. Inspired again Burkhard!
Was in situ strength maintained? Firing paper in ceramics causes problems but you say it worked with the metal, do you think it increased the porosity? Burnishing prior to firing ceramics is an old technique to compact the particles, I wonder if this might apply to the metal clay and reduce porosity.
Did you use a variety of particle sizes for the bronze powder somewhere I think I read a ratio of 7:1 small to large gave greater sintering strength and reduced porosity, same article said the firing cycle for the wax bronze was 24 hrs which would imply a longer cooling period. Is the proportion of crystalline wax to parafin critical?
Could anyone help with where to get metal powder in the UK coz I think its time for the burning boom! stuff here too.

[Harryman]

Any thoughts on forming the clay over a core that could burn out? Less mass of clay would mean less shrinkage, maybe less cracks. Or is this stuff too friable to hold up in a thinner layer?

[jphariot]

Hello Burkhard,
Thanks for the response. Now your saying that you have not had good results, but that initial bronze statue that you have photographed is not bad for a start.
Quite encouraging really.
Now, I wasn't sure about your response to using Methyl Cellulose, Like PMC uses. Do you mean that you tried it, and it did not work well? Or you have not tried it yet?
The PMC seems to be really easy to work with, and basically full proof. Actually, I ordered some Methyl Cellulose from Dow and should get it today or Monday. I already got some Bentonite. What doesn't make sense about Bentonite is that its a ceramic right? So I would imagine that It would NOT burn out, but stay in with the Bronze and bond or "alloy", if you will.
Also, I made an Aluminum Powder-Bentonite clay test peice. It is drying right now. I imagine that Aluminum would not oxidize prior to sintering?

Good Idea about using the paper pulp. Theres a Japanese product called Paper Clay, I think it also has volcanic ash in there. I have it in a drawer, in an opened package. Got to get around to it, but that has been in the back of my mind for a few months.

Also, enitharmon has an interesting idea with the sugar. Keep us posted of any developments.
And Harryman, about the core issue. I think that PMC makes a cork material that they use as a core. As far as I have read it works fine. See Rio Grande catalogue. Or maybe Riogrande.com I think is the site.

Now, Burkhard, I have a few more questions about the Gas-vacuum issue:
What I did have in mind for vacuum was as you mentioned to place a small electric furnace inside of a steel vacuum chamber. Its easy to just drill holes into the vacuum chamber and run wires through, Pyrometer etc and seal them with epoxy. I do have a nice welch vacuum pump.
BUT!! if nitrogen is easier?? Then why am I going to build a vacuum right away. I am ignorant about nitrogen. What kind of safety issues is there with nitrogen? So I would place a stainless Steel pot with lid inside Furnace, where I then place the Metal clay piece into, correct? And theres a stainless steel tube running into the stainless pot. Correct? I guess this means that I cant sinter stainless steel parts with this system. Got to stay with CU based alloys or silver- gold etc.
But, If CO2 works fine??? I remember using CO2 for sand casting core molds that I tested a few years ago. Does the CO2 work the same way as the Nitrogen? Any safety cautions? CO2 explosive in 1800F environments? I should have taken chemistry in college. Would you suggest CO2 instead of Nitrogen?
Also, do you have any more photos of your more recent sintered Bronzes?
Lastly, If I can get this to work with these binders in question, I think that the next step would be to maybe use a binder that will not air dry. Time consuming and conducive to cracking. Good to start with, but I am already wondering about Sodium Silicate, which cures immediately under CO2, or they have some one part epoxies now that set at 250F. I am getting ahead of myself here, so for now, I am going to focus on making this work. I will post photos when I get my first success.
Thank You,
John Hariot

[Burkhard]

Hi enitharmon

Was in situ strength maintained? Firing paper in ceramics causes problems but you say it worked with the metal, do you think it increased the porosity? Burnishing prior to firing ceramics is an old technique to compact the particles, I wonder if this might apply to the metal clay and reduce porosity.
Did you use a variety of particle sizes for the bronze powder somewhere I think I read a ratio of 7:1 small to large gave greater sintering strength and reduced porosity, same article said the firing cycle for the wax bronze was 24 hrs which would imply a longer cooling period. Is the proportion of crystalline wax to parafin critical?

WRT the bronze paper clay: I tried 4 samples with 95g bronze powder, 5 g bentonite and approximately 0.25 g, 0.5 g, 0.75 g, 1g of paper pulp added (paper pulp was simply tissue paper that I blended with water using a paint mixer attached to an el;ectric drill). After firing I couldn't see any difference in external appearance. I haven't cut the samples in half yet, and looked at them under a microscope, to see if there are any internal differences, but all seemed to be "solid" bronze pieces and couldn't be twisted/broken by hand. The idea came from the fact taht I use "paper clay" routinely for the "normal" sculpures that I do - this stuff is just ordinary clay mixed with some paper. The paper allows you to join clay that is almost dry and then fires quite normally.

The bronze powder I used was what was available to me over the internet from the local sculptors supply company and is the stuff used for cold cast bronze where bronze powder is mixed with resins to produce the bronzy looking resin casts. I have no idea at this stage what the size distribution of the particles is. A quick look under the microscope only revealed that there were aggregates (50-100 microns) as well as particles below 5 micron in diameter. I figured this was good enough for a first attempt.

I think for the firing of the bronze wax, the firing cycle is far more important than for the bronze clay. Especially the decomposition phase for the wax.

In terms of wax composition - sorry, no idea. I know that when I used "jewellry" wax, used for casting jewellry findings, all I got was powder, but this could have been due to other problems at the time.

I came across a paper that looked at slumping of sintered bronzes. Two findings were that at about 880C the sintered bronzes had achieved their maximum density (about 90% of theoretical maximum) with virtually no slumping/distortion but that the amount of slumping/distortion increased rapidly at temps above 900-910C. In future I'll take the temp to 880C not 900-910C as I have been doing. Given that pyrometers are also not that accurate I may have been overheating my kiln.

[Burkhard]

Hi Harryman,

Any thoughts on forming the clay over a core that could burn out? Less mass of clay would mean less shrinkage, maybe less cracks. Or is this stuff too friable to hold up in a thinner layer?

When I did the hand formed figure I did use a small core of tissue paper wrapped in a small plastic bag. The figure was formed over the top and after drying a little bit I carefully removed the core, and then allowed the bronze clay to fully dry. I suspect that just like ordinary clay, allowing the clay to dry over a solid core would lead to cracking. I've never used the cork core used with PMC.

Linear shrinkage of the bronze clay on drying was approx 9%, after firing it shrunk by another 10%.

[Burkhard]

Hi John,

Sorry if I tended to sound too negative about the results so far, I'm actually quite pleased with it and you should have seen the jump for joy :D when I took the very first sample out and it looked solid and like bronze. I guess I'm a cautious type and don't want to give people a false impression that everything works perfectly. Also I'm trying to be cautious in terms of saying what will and what won't work - quite often something that won't work for one person will work for the other, who does things just a little differently.


I tried adding some methyl cellulose to the bronze clay. I made up a 1% wt/vol solution of the Me cellulose in water and used that instead of pure water when making the bronze/bentonite clay. I also tried adding a small amount of olive oil to see if I could make it less sticky. On firing, a small figure made from this was just dust after firing, even though another sample next to it made from the ordinary bronze clay was fine. I read somewhere that depending on the type of binder used and the heating regime it is quite possible to coat the bronze particles with carbon residue from the decomposition of the binder which can prevent them from sintering. This may be the case for the Me cellulose. Remember that the silver PMC is fired in air, hence the binder can burn out, whereas for the bronze powder, we're heating in absence of oxygen, i.e. no burning only decomposition of the binder. Also, in the bronze wax method, the wax is first wicked out into the aluminium oxide powder (leaving a bronze powder with virtually no organic matter in it) and then it decomposes in the aluminium oxide powder not while touching the bronze powder. I'm very curious to see if you have any luck with it.

Yes the bentonite won't burn out so the bronze clay will give an "alloy" that's about 85% copper, 10% tin and 5% bentonite. The original patent actually calls the water the "binder" and the bentonite the "plasticiser" for the metal clay.

WRT the aluminium - aluminium oxidises so quickly that all aluminium has a layer of aluminium oxide on the surface. If you make pristine aluminium powder and expose it to air it can actually spontaneously catch fire because the rate of oxidation is so quick and vigorous. So, the Al powder that you have will certainly already have this layer of oxide on it. Whether the oxide layer is thin enough, porous, brittle enough etc to allow sintering betwen the Al metal cores of the particles - hopefully you'll be able to tell us soon :) .

In terms of the gases: I really don't know enough about engineering of vacuum chambers to give good advice here, except if you use a vac pump I really don't think you'll be able to do the bronze wax stuff because the soot etc will gum up the pump (also not sure whether the pump is rated to pump flammable gases).

If you can set up a vacuum chamber you certainly should have no problem setting up a gas line and a steel pot inside the furnace. I'll try and take some pictures and post them in the next day or so.Trying to sinter steel in a steel pot would be touch and go. You might be able to get away with it as for sintering you want to stay clear of the melting point (and even the slumping/distortion temp) of the material your sintering.

Common inert gases are argon, nitrogen and carbon dioxide. I've tried argon and carbon dioxide and am sure that if these work then nitrogen will as well. An advantage of argon and CO2 is that they are heavier than air and so will form a better gas "blanket" in the bottom of your kiln pot.

The gases are not toxic by themselves i.e. you won't be generating toxic fumes by using them, they won't explode at 900C. I was initially worried that the CO2 might chemically react with the copper to form copper carbonates at high temp and hence stop sintering - this doesn't seem to be a problem.

The main hazard with these gases are that in enclosed spaces they will displace air (oxygen) and and if you happen to be in that enclosed space you will asphixiate and probably die. However, if you're setting up a kiln to operate in an enclosed space without good air circulation then you probably shouldn't be doing this stuff anyway :) .

As asphixiant nitrogen and argon are more dangerous than CO2, because you can't tell when you're breathing pure nitrogen (or argon). When you hold your breath and you feel the need to breathe that's the CO2 level in your lungs increasing. The body has sensors that can sense this increase in CO2 and it tells you to breathe again. The body has no sensors for nitrogen or argon (or oxygen for that matter) so if you breathe pure nitrogen you will continue to breathe perfectly normally with no sense of asphixiation - and you will have (literally) just enough time to say "oh bugger" as you fall to the ground, never to get up again. Unfortunately this happened a couple of years ago at work (three fail-safes all failed at the same time, the poor guy walked about two steps into a nitrogen filled room, end of story).

As I said, with normal ventilation (e.g. open window or doors) there should be absolutely no problem. I like CO2 because for me it's cheaper, it's heavier than air so will probably be better at excluding air in a pot with a leaky lid, and if by some absolute freak occurance the CO2 levels increases where I'm working I will know.

I was wondering about the sodium silicate but wasn't sure how alkaline/corrosive the stuff was. Certainly worth a shot though. I'm still curious whether part of the reason why the bronze clay work is because on drying the bronze particles are pushed close together until they touch.

Good luck everyone!

[Harryman]

Appreciate all the effort your putting into this project Burkhard, you're making great progress. I'm really enjoying watching it come along.

I've built a few vacuum systems and it would be a lot easier to flood an area with an inert gas than to try to eliminate all leaks in a vacuum system, especially one operating at a high temperature. Not to mention getting a pump to operate well under those conditions.

I agree that CO2 is a great way to go, it's easily available, relatively cheap and pretty hard to kill yourself with.

There's carbonated springs in my area that some of the local kids used to use to get high. They'd lay in the hollow by the water where the CO2 had displaced some of the O2 untill they felt light headed. Great fun untill someone lay a bit too long. Ignorance or evolution in action, take your pick.

[jphariot]

Burkhard,
So, the aluminum tests I did proved what you are saying. In fact thats what I thought yesterday. I looked at the powder and it really did not seem shiny. So I figured that it is already oxidized.
But is there an aluminum powder that you can get that is NOT oxidized?? I am pretty sure that they do sinter aluminum,so there has to be, I would guess.

As far as the Methyl Cellulose. It sounds like you didn't try it alone without the Bentonite, so do you think that there might be a chance that it works under vacuum with bronze, or with CO2? Or it won't work?
If that is the case, maybe we could just use it with silver powder in an oxygen atmosphere like PMC. Why not just buy PMC then? Well, it is about twice the price of silver on the market. Not sure its worth making an in house version with available powders?

Now as far as the Gas vs Vacuum, I think you have sold me on CO2.
My kiln is outside to top it off and when I have one inside, I will always open the doors. But to make sure, I am not sure what it is about CO2 that you could detect? Do not quite follow that.
Now what might also be an added benefit to CO2 is if by chance we could use a sodium Silicate binder, then the CO2 could be used to cure the binder, and it cures quickly. I mean in maybe like 30 seconds or 60 at the most.
I was attempting to make small sand molds with undercuts. So I had urethane molds that fit into a wood box. Then I would pack the molds with sand and Sod. Silicate. Then you put a lid with a hole and stick the CO2 tube into that hole and give it gas. Any way you can figure to impermeate the sand mold should work. And soidium silicate is cheap and water based. The only question is, what happens during sintering?? Thats the million dollar question. Well, I can try it and find out. But first I need to try the Bentonite, CO2 and Methyl Cellulose.
Now that first sculpture, ( the image you posted), you said that it cracked coming out of the silicone mold. I figured you already thought of this, but still, what if you placed it in a thin dryed out plaster mold? Like in Ceramics, I should suck the moisture out of the bronze clay. But a hard mold of plaster will not be forgiving as to demold the Bronze Clay. So you would have to break the plaster, Dissolve it in Muriatic Acid???, or place the whole thing with bronze clay still inside the plaster mold , into your Kiln or furnace. Think that might work?
I can totally believe how excited you were when you pulled out your first piece. I plan on getting that CO2 this week, if I can, or the next and making it happen here. One last question about CO2. How much are you using? Or how much do you introduce into your stainless steel pot? You must have a regulator with an amount?
Thanks again, and I am looking forward to seeing more pictures of your Bronze pieces.
John Hariot

[jphariot]

Burkhard,
Some more thoughts or questions just popped into my head as I was casting pewter.
I have a local surplus that sells all kinds of tanks. Is a CO2 tank that same as Nitrogen, argon etc. In other words, does the tank have to be specific to CO2?
Same with the gauges? Unique gauges that only work for CO2?
Also, I was thinking, if the aluminum powder is oxidized, when you buy Bronze, or copper etc, how do you know that that powder isnt already oxidized??
My bronze castings or copper pipe sitting around darkens. Maybe the fact that its in a closed container is enough to keep it un oxidized I imagine. But I am surprised that aluminum powder doesnt do the same and stay nice and clean.
I am actually alloying some metals right now,Without phase diagrams, and aluminum is somewhat resistant to darkening. Better than tin or Zinc for sure.
Hopefully soon, I will have more results and answers to post instead of questions.
Thanks again,
John Hariot

[Burkhard]

Harryman - Thanks for the kind words. I once had a long discussion with a friend of mine re evolution. He argued that once a creature (such as mankind) develops civilisation and generally takes care of its weaker citizens, then evolution stops. I maintained that there's plenty of stupidity left in the world and that evolution is alive and well. That was 20 years ago - nothing I've seen since then has made me change my mind. More's the pity.

[Burkhard]

Hi John,

Yes, different gas cylinders do have different regulators with left threads, right threads etc. This is to avoid accidentally screwing in an oxygen cylinder, a flammable gas (e.g. hydrogen) into an inert gas line etc. You can use the same regulators for nitrogen and argon, but carbon dioxide has a different fitting (different type of regulator compared to nitrogen because CO2 can form dry ice if released from a cylinder too quickly, hence it requires it's own type of special regulator). Also, for the same reason you would not be allowed to fill a gas cylinder with any other type of gas than the one it was designed for. They are all colour coded as well.

In terms of oxidation - all metals (with the possible exception of gold, which has all sorts of other junk adsorbed on to its surface) will have a layer of oxide on it when you buy them. This includes any bronze powder or other metal powder that you buy. The question is "how much oxide?" Answer is - no idea! Sorry. This will depend on the history of the sample, how old it is, whether its been exposed to moisture etc. I think it may be a trial and error thing in terms of supplier. If one wanted total reliability I guess there are chemical reduction methods to remove any oxide from the bronze powder if neccessary, but this would add another layer of complexity which may not be neccessary. A closed container is good, but reality is that it is extremely difficult to seal a container such that it is truly gas tight.

The other thing to note is that different metals form oxides with different mechanical properties - aluminium oxide forms a nice strong, impermeable oxide layer on the aluminium which prevents further oxygen from penetrating to the surface of the aluminium and oxidising it - the reaction is self-limiting i.e. it stops after a layer of aluminium oxide is formed; iron oxide does not form a nice, coherent oxide layer - it keeps flaking off/lifting of the surface exposing more iron, which oxidises etc etc until you just have a pile of rust and no more iron; chromium forms a very thin, inert oxide layer which prevents further oxidation but is so thin that the metal shines through. Bronze is probably intermediate, it will form an oxide, but the oxide layer is not so perfect that it will prevent sintering (if the oxide layer is thin enough, strongly oxidised (old) powder may be a different story).

To make aluminium powder that does not have any oxide layer would be extremely difficult (requiring ultra high vacuum etc). As soon as its exposed to air it would form an oxide layer. If people sinter aluminium, then maybe it's a case of how thick the oxide layer is?

The Me cellulose is probably what is used in silver PMC (certainly what Mitsubishi Metals describes in their patents). When I tried this a couple of years ago I could certainly form a silver/me cell mixture that could be sintered using a Bunsen burner. I never followed this up further because I couldn't see myself doing 10" - 20" silver sculptures, and that's the size range I like working in.

Plaster mould - yeah I have wondered about this. I suspect that it would work in the same way that it would work for ordinary clay. May even be possible to do some bronze clay slip casting? Just like ordinary clay, I suspect that if you do a press mould into a dry plaster mould, then as the bronze clay dries slightly and shrinks it would pull away from the wall of the mould and it would be released quite readily. [I would keep hydrochloric acid (muriatic acid) away from the bronze clay - HCl would dissolve/etch the bronze]. But, I keep sort of hoping that the bronze clay is useable without any mould making being neccessary - I'm fundamentally a lazy person.

The gas flow rate that I use is about 200 ml per minute. THis is an arbitrary number - I have no idea whether it should be more or less, but it seems to work. I do have a gas flow tube that I use to monitor flow rate, but I guess that you can probably calibrate the flow rate (attach a plastic tube to your regulator, fill a drinking glass with water and invert it in a bucket of water; place tube under water underneath glass and time how quickly the drinking glass fills with gas; adjust regulator to get appropraite flow rate, make a mark on the regulator so you can set it to the same approximate rate each time).

Unfortunately my camera died today so no pics until I get another one.

With regard to what you detect when CO2 level is too high - you would feel the same way as if you had been holding your breath, or as if you aren't getting enough air i.e. you would know something is wrong and if you recognised the feeling you may have a chance to do something about it i.e. head outdoors. With nitrogen or argon you would not get that feeling at all, you'd just fall over. Very painless. However, I don't want to scare you or anyone too much - the possibility of asphixiation in a normal sized room with a window, with one of the small gas cylinders is very remote. Just something to think about though when setting up. When I pick up my gas cylinder I do drive with my windows down - just in case :)

[enitharmon]

Thanks for the detailed advice Burkhard. I get enthused and too often take shortcuts...but as they say shortcuts lead to long journeys and in these experiments possibly very long journeys!
If I can go back to your experiment with bronze wax mix did you use epolene in the feedstock? I found a masters thesis analysing proportions of wax and polymers for sintering stainless steel. I imagine the principles are the same for bronze. Wetting properties of the powder with surfacants were examined. Stearic acid was used and improved the viscous flow. Viscosity was also lowered as the proportion of paraffin was increased and variety in the particle size allowed a greater porportion of metal powder to be added, though this also affected viscosity. Dr German's article mentioned the improved in situ strength of the feedstock with varied particle sizes and a 2 hour hold temperature for sintering controlled at 840c.

The volatile gases you mentioned were a problem. Would the gas flow from the nitrogen cylinder push the gases out of the saggar chamber through the tubing toward ignition if the chamber was firmly sealed and solve the gas problem? When you poured the mould did you use a release agent...fairy liquid or something? I wonder if Mark could advise us on his tricks for the slush mould..

[jphariot]

Burkhard,
I am glad I read this before I left out to the suplus to get a cylinder.
But there is a beer and wine place that has a used CO2 tank, and they can fill it too. They also sell gauges. I imagine that the gauges will allow me to read 2o ml per minute? They may be psi or something else? Iwill see when I get them. I think I will go there today or tomorrow. Thanks for the excellent info!
Now I was wondering if the Methyl Cellulose would produce dangerous gasses in the CO2 atmosphere? The kiln wont be air tight, so I imagine that the Co2 will escape slowly and so will any gasses produced by Methyl Cellulose. What do you think?
But I will be trying the Bentonite first. I was wondering if the Bentonite makes the Bronze pieces very brittle? Can you actually bend your sintered pieces like you would normal Bronze?
And do you keep your bronze clay in a sealed container?? I think it would be great to be able to make a large bunch of it and store it for next day or next weeks use. But would the Bronze oxidize in the moist atmosphere of this clay??
I actually ordered 2 different samples of Bronze powder today. One is the smallest particle size they had 23 Microns. Its not all 23, they said some are smaller and some bigger. I guess 23 is an average.
The other company measure in "mesh" and it was 100 mesh and also a 60 mesh.
But the saleperson said that people buy 325 mesh for sintering from them all the time, so I figure it will be good enough.
So, just to check again, I will be buying a stainless steel pot and drill a hole in either the lid or the side. Then I will run a stainless steel tube to the outside of my kiln. (bore a hole into my kiln). Then on the outside I can run my CO2 tank that is connected to the rubber hose, that connects to the stainless steel tube. And also place a weight on top of the stainless steel pot lid to make sure its not leaking too much. Kind of snugg.
Then sinter!!!
I am also thinking about sintering stainless a few months down the line. I imagine a refractory pot with lid could be made. And instead of Nichrome wire, , a kanthal element could be used. Doing stainless would be an absolute delight. Hey, I guess we wouldnt have to worry about Stainless powder oxidizing at room temperature. Im sure it would oxidize at 1500F. I know that by the investment casting flasks. Once they get red hot they start to oxidize.
What is you next step in your sintering tests??
Thanks again!!!!
John Hariot

[Burkhard]

Some pics of my current set-up. I blush at the crudity of it :o

Pic 1: CO2 cylinder with regulator attached, plastic tube leading to flow meter that I use to measure gas flow rate (this is not essential as it should be possible to calibrate flow rate crudely and then make a mark on the pressure gauges to set flow rate). Note that for this pic the cylinder was not attached to anything. You should always tie the cylinder to something so it can't fall over accidentally - either attach two hooks to a wall and put a chain around the body of the cylinder or attach it to something sturdy so it can't fall over. I currently use an old leather belt to tie the cylinder to the legs of my workbench. If you don't tie the cylinder down sooner or later you will trip over something and knock the cylinder over - worst case scenario: the main valve breaks and your cylinder becomes a rocket that launches at the nearest wall.
http://i154.photobucket.com/albums/s280/Burkhard_photos/Direct%20Bronze/setup1/DSC00720.jpg

Pic 2 Just showing the gas cylinder attached to the steel pot that's sitting in the kiln. A bit of plastic tubing attaches to the steel tubing.

http://i154.photobucket.com/albums/s280/Burkhard_photos/Direct%20Bronze/setup1/DSC00722.jpg

Pic3 Top view of kiln and pot. Note gas inlet line on left and outlet line on right. I used a hacksaw and screwdriver as a chisel to carve out two trenches about 1/4" deep and 1/2" wide for the steel tubing to sit in so the lid of the kiln closes. I went through the top raher than through the observation hole because I want to be able to remove the pot easily if I decide to use the kiln for ceramic stuff. Pyrometer sits in observation hole. Also note the three steel weights that I plonk ontop of the lid of the pot to hold it down. This does not however give a gas tight seal around the lid. I've attached the outlet steel gas line (with a simple screw valve attached) if I want to play with the bronze wax stuff. However it turns out that my lid leaks so much that I doubt whether this is that useful.
http://i154.photobucket.com/albums/s280/Burkhard_photos/Direct%20Bronze/setup1/DSC00721.jpg

Pic 4 The steel pot. Note the lack of protruding handles that could contact any live wires inside the kiln. Pot is a 14 liter stockpot, about 10-11" diameter and about 12-13" depth. Still looking for larger pots, but I may have to get something built special at some stage.

http://i154.photobucket.com/albums/s280/Burkhard_photos/Direct%20Bronze/setup1/DSC00716.jpg

Pic 5 Close-up of the way I connected the steel tubing to the pot lid using "swagelock" connectors (see previous post from 28/5 for part no.)

http://i154.photobucket.com/albums/s280/Burkhard_photos/Direct%20Bronze/setup1/DSC00717.jpg

[Burkhard]

Enitharmon - never sell entusiasm short! I tend to always try the quick and dirty experiments first - usually the most fun if they actually work and I'm not a patient person. I am however an extremely stubborn person - a thick skull helps when continuously running into brick walls.

I've not tried the epolene - I figured it had something to do with mould release/shrinkage properties of the wax. It was also too difficult to get here. I'd be curious to see if it did make a lot of difference. With the stearic acid I got as far as making up some bronze wax samples using 10:1 microcrystalline wax/stearic acid but never got around to firing the samples - the bronze clay came along.

The gas evolved during the bronze wax firing will get pushed out the exit tube by the inert gas. You need to place a burner e.g. propane gas burner at the exit line to combust all the carbon monoxide and hydrocarbon gases at the very least. If your pot is not gas tight some gas will still escape into your kiln. If you're using a gas fired kiln this is not an issue, if using an electric kiln then I get worried that the gas build-up could cause flammable gas mixtures leading to explosion hazards or at least to a build up of toxic gases near the kiln.

For the bronze wax poured into silicone moulds I didn't use a release agent. The stuff released fairly easily, just like ordinary wax.

[Burkhard]

John -

With respect to the Me cellulose - any organic material that you add to the clay or wax etc will decompose to give a variety of flammable and toxic substances including carbon monoxide (highly toxic, odourless gas). The CO2 will only serve to prevent the Me Cell from burning out to give CO2 and water and will actually be the cause of producing the flammable gases/CO. As I mentioned to enitharmon, if using a gas kiln this is not an issue, but for electric kilns any gases escaping through the lid in an uncontrolled manner could pose an explosion or toxic gas threat.

Not sure whether the bentonite makes the bronze brittle - haven't been able to bend any of the stuff I made with the 5% bentonite. Adding 10% bentonite did allow me to crack a sample when applying a reasonable amount of force in a vice.

I did one set of samples a couple of weeks ago where I made up the bronze clay and left it in a sealed container. and then made up sample ingots on day 1, 3, and 7. All fired OK i.e. it looks like you can store the stuff. However, I did notice green water-soluble material coming out of the damp bronze clay - I presume it's copper carbonate. Not sure how this will affect the longer term storage ability of the bronze clay, but certainly a few days storage of the damp clay doesn't seem to be a problem.

I've made up a slightly larger batch of the bronze "paper' clay and am hoping to try my hand at sculpting something directly by hand with this stuff. Not enough time...

Good luck all

[jphariot]

Burkhard,
Thank you for the images. What kind of connector are you using to connect the 1/2"??? Stainless Steel tube to the pot lid? Is that a plumbing fitting? Not sure I recognize it.
As far as the binders causing dangerous gasses in the CO2 atmosphere, wouldnt that be different under vacuum? wouldnt the gasses go out into the vacuum and into the air? But I imagine that the area where it comes out of the vacuum would still be either toxic and or flammable.
Are there any binders aside from Bentonite that might not do this? what about Sugar? would that produce dangerous explosive gasses? How does one guess ahead. Wax I could understand because it is very flammable, and I even read nasa is working on a Paraffin fuel.
I plan on starting with Bentonite. It is going to be exciting to get a first piece to work. But I do figure that 5% bentonite would make the Bronze Brittle. In most cases I wont care, but some things I want to do may require some bending or crimping. I wonder if we can get away with a smaller amount of bentonite?
But even aside from that, Ideally it would great if you could use a binder that does not need to air dry. The hang ups I can see, is silicone molds want to keep the parts moist. And Plaster wants to keep the part locked in. Especially if you have negative draft. Meaning undercuts. And I love undercuts. That gives one so much freedom. So, if we could use a binder that hardens with heat, co2 gas, microwave??, catalyst that would be awesome.
I would want to shy away from urethanes or epoxies because I cant even imagine the toxins coming out of those when you sinter. Imagine that they sell urethane binders for sand casting. How long can a metal caster live breathing that all day?
But would a sodium silicate, which I was told is basically sugar, produce dangerous gases? I could see that possibly working. I would be willing to try.
What do you think?
One last question. I am not sure how you upload photos here? I could display the progress.
Thanks again,
John Hariot

[Burkhard]

John,
the connectors are called a “stainless steel Swagelock bulkhead union for ¼” tube” (Part No.: SS-400-61) Have a look at the swagelock website - they have dealers everywhere or can be bought over the net (Swagelock.com). I think they cost about $25. They just require you to drill a hole in the pot and then using two pliers one can connect the tubing.

Organic materials (e.g. waxes, polymers, sugars, cellulose PVA, epoxies, urethanes, resins etc) are made up of carbon, hydrogen and in case of sugars and cellulose, oxygen. Sometimes also nitrogen sulfur etc.

If these materials are heated to 250-450C in excess air then basically you get combustion i.e. you end up with the oxygen combining with the carbon and hydrogen of the organic material to produce harmless carbon dioxide gas and water vapor.

In the absence of air (either under inert gas or in vacuum) when these compounds are heated to 250-450C the carbon-carbon, carbon-hydrogen, carbon-oxygen etc bonds start to break/recombine/break and a complex mixture of stuff is produced e.g. methane, ethane, propane, carbon monoxide, as well as carbon soot etc etc. I don't think there's any way around this if you're using an organic based binder.

Sodium silicate is not sugar. It contains no carbons, only sodium, silicon and oxygen (+ water, + hydroxide I think), hence it will not decompose like organic material but will remain in the bronze, forming a silicate. Mind you, I don't know what will happen to the carbonate formed from the CO2 used to set the sodium silicate when you heat it up - I'll have to look into this. Bentonite is an aluminium silicate, so in some ways not that dissimilar. I suspect that before firing the "silicate/CO2" bronze you'll still need to dry it. Very interesting idea though and definately worth trying.

FYI: I came across a German patent (DE 43 43 420 A1, from a company called Sinterstahl Gmbh) where they give 3 examples of a kneadable mass that can be set by applying a spray hardener (rough translation from the German follows):

1) take 1000g steel powder (<44 micron size), add methylcellulose/water (1:40 mixture, 60 g), ethylene glycol (15g), glycerol (15 g), ethanol (2g), olive oil (5g), polymethylmethacrylate (product name Plexisol, 20g). Mix ingredients 1 hr, add polymethacrylate, knead further 0.5 hrs. Form by hand as desired, dry 24 hrs in air. Then place in bed of sand, heat under inert gas to 120C, then to 120 to 650C at 10C per hour, keep at 650C 1 hour, heat quickly to 1250C and keep there for 1 hr.

2) 1000g bronze powder (<160 microns), add 125 silicone resin, 50 ml silicon oil, 30g detergent, 10g of solvent for detergent. Knead everything together. After forming the object, spary the object with the appropriate hardener for the silicon resin in order to set the material. Fire as above but finial sinter temp 830C and left there for only 30 min.

3) Material as per example 1, except olive oil and Plexisol where left out, and instead 10 g of methylacrylate was added. After forming a suitable hardener for methacrylate was sprayed on the form to polymerise the methylacrylate. Object was then fired as per example 1.

Note methylacrylates and similar compounds can be very toxic, not the sort of thing one wants to form by hand. If people do decide to experiment with different binders etc please please check the MSDS sheets (usually available on the net) for any toxic properties of the materials that they play with. The patent does not give any further details as to the exact resins, hardeners etc that were used.

In terms of photos - I did take the advice (given somewhere else on this board, sorry don't know where now) of signing up with photobucket (at photobucket.com). It's free, and seems harmless so far. Once you've uploaded your images to photobucket from your PC look underneath the photo. There are 3 links there - if you cut'npaste the one starting with img (the bottom one) into your "reply" on this board then it should magically appear.

[DanielUCM]

Burkhard - Thanks for the pictures of your set-up and for the additional information!

John - I have for some time been pondering the issue of being able to cast undercuts etcetera without having to use a wax binder. I thought I had come up with a great idea but found that as usual I wasn't the first - the idea is freeze casting. I will give some more information and a couple of good articles after I have done some initial tests myself - I want to know what I am talking about before saying to much! Hopefully I will get my new kiln on friday - hopefully - so I can start doing some experiments. I can't use the gas-kiln where I live right now so I have had to get some better equipment.

The idea with freeze-casting is to mix the steel or bronze powder with water and a few important additives that increases the wetting and decreases the ice-chrystalls. Cast this in the silicone mold, freeze and put in the aluminium oxide and sinter. It is also possible to add some more stuff and freeze-dry it to increase green strength.

Like I said I will get back when I have been able to do some initial attempts in the kiln, but I have already tried the freeze casting part of the process and it seems really promising so far as regards making thin/undercut castings!

By the way, thank you guys for coming up with new angles and for handling Burkard all those questions, it's really beneficial

/Daniel

[jphariot]

Burkhard,
Thank you for the swagelock info. I will most likely purchase one or two, but for the first test, probably just use a high temp adhesive, because I have them here and its cheap and easy.
I also just got a 3' tall co2 tank. It has the valve on top with no regulators.
I think for the first test, I could just open the valve up and allow what would appear to be a "reasonable" amount out. Just for the first test. Do you think that would work? Then if I think, I am going to stick with co2 and not go to vacuum, I will get some regulators. Just trying to save time.
Thank you very much for the sodium silicate and other chemistry information.
It is starting to make sense. Yes several salesman told me, when I was purchasing Sod. Silicate, that "its like sugar", or "its glorified sugar". Salesmen will say anything!!.
Now, did you know that you could harden Sodium Silicate with CO2? It really works quite nicely with sand. Why wouldnt it work with metal? well, the sand is a much coarser grade. The finer the grain the tighter seal and the harder it is for the co2 to permeate. But maybe it just takes more time??? I will try it and let you know.
Very interesting German patent. Thanks for the toxic warning. Your German must be pretty good to translate that.

Now Daniel is onto something interesting!!! I spoke to some guys a few years ago that were working with ice/water for rapid prototyping. Instead of the corn starch or polymers etc, they were using ice. The images of the stuff looked ok. But it seemed real tricky. 3D rapid protoyping is tricky by its very nature. Theres a lot of machines sitting around and not working all that nicely.
But, by using silicone molds that could be a totally different story.
So Daniel, how does the metal powder stay together once the ice turns to water? You mentioned some other ingredients, but it sounds like they are just there to aid in the freezing process.
Does it stay together, due to the aluminum oxide encasement?
I know absolutely nothing about freeze drying. I will google it later today, but you say it works well?
Now I have another idea I will share with you lads. This would only be worth it for a part with undercuts and if you had to make, maybe a dozen or more.
Casting 2 part thin shelled plaster based molds. Then you simply pour DRY metal powder into a small hole with vibration. Should fill out very nicely.
Now place into kiln slowly ramping it up. The plaster molds dry out and then you raise the temp to sintering. Once sintered you drop the whole mold and part into water. The plaster mold will dissolve like mud within half hour, and you pull your part out of the bucket of water. I wonder if the steam coming out of the plaster mold when drying will adversely affect the powder? I kind of dooubt it will.
What do you lads think?
Kind Regards,
John Hariot

[Harryman]

Interesting idea using the plaster for support. If you placed your bronze clay piece in a container like a casting flask, poured investment around it, fired it, quenched the whole thing, the investment would be gone within 10 seconds because of the thermal shock. You would only need the binder to support the clay as you worked it, not while it was fusing.

If you ramped up your kiln slowly, let it sit to burn off the wax, I wonder if you could use the wax based binder Mark was using? The investment would absorb the wax just like his powder.

[jphariot]

Harryman,
I would imagine that the plaster would absorb the wax. But I think packing it with Alum. Oxide powder it quick and easy to do.
Well the idea with the plaster mold would be to ramp it up slowly. Like you do when your drying a mold. It should be fine througout the sintering process.
I am going to try it. I think it could work.You see I have some complex parts with tons of undercuts I must make. Investment casting gives me nightmares.
I actually have to start preparing today, but I would be exstatic if I could atleast make some of the parts using powder or Clay.
I am also still thinking about Daniels idea of freezing.
Daniel, please keep us posted as to how that is coming along. Are you willing to let us know what these other ingredients are that keep the water from crystallizing?
Also, a question for Burkhard: As far as the gasses that would be created by Methyl Cellulose with the CO2 atmosphere inside the kiln. My Kiln is outdoors. I used it to fire investment molds. So what if I just bored a 1" hole into the side of my kiln and put a cpu-computer fan on the outside. Wouldnt that pull out any potentially toxic and flammable gasses? I would imagine that should be all I need. RIght?
Thanks!
John Hariot

[DanielUCM]

Harryman - I have only used ceramic shells myself but the reading I have done on poured moulds have me believe that one problem could be the forming of air-bubbles next to the piece. The nice thing with the Pilato style powder suspension is that there is zero problem with bubbles. If one has been able to get a bronze clay/wax type figure I think the powder suspension is the best option (unless when using the bentonite formula (?) or some other method which gives strenght even after the initial heating).

John - I will get back with some more info on the freeze-casting, as for the two-piece mould I think that could possibly be great when one wants to make a bronze clay design that is really thin or as you say have undercuts. Another thing - when making normal bronze casts it's not possible to make parts that are too thin since the pour might stop in cramp passages, as I have understood it. But if you shake down the powder in a plaster mould it could probably be made a lot thinner. However the ideal would be to use a method which allows us to get pieces that are strong enough straight from the silicon mould (or straight from the hands) instead of having to do new plaster moulds for every piece. I have however no experience with making plaster moulds so I don't know how difficult it is.

I would imagine that in the end we will use different formulas for different pieces. One when the shapes are less demanding or when no mould is wanted and one when the forms are more demanding with thin passages and undercuts.

/Daniel S.

[Harryman]

I've used poured investment for 20 years, bubbles are easily eliminated, the container can be vacuumed or vibrated to pop the bubbles off the piece. There are also solutions you spray or paint on first to reduce the surface tension so they come off a bit easier. No biggie.

The investment is porus too, so the CO2 should be able to keep the bronze clay in a non reactive environment.

The advantage over ceramic shell is that it's a lot quicker. Mix it up, pour, wait 2 hours and pop it in the oven. There are also high temp investments you ramp straight to your highest temp right after set up. They're a little pricey though for sculptural sized stuff.

I haven't made up any clay so I don't know how rigid a support is needed, if it's pretty self supporting, I agree the powder would be an easier way to go. If you could use a binder that burned out cleanly at low temps though, invesment would be a good way to keep the piece together till it fused.

[Burkhard]

jphariot - I would very very very strongly advise against cracking open the main valve of a gas cylinder without having a regulator attached!!!

The force of the gas is huge and can't be controlled with the main valve. You could do yourself a serious injury e.g. loose your eye. Also, with CO2 it'll probably freeze it creating dry ice - again a hazard. Please get a regulator.

[Burkhard]

Hi all, great to see all this activity.

My main misgiving about using a rigid investment mould around a bronze wax, or pouring powder into a rigid plaster mould is whether there would be distortion as the bronze sinters and shrinks. I suspect that part of the beauty of using a fine Al2O3 powder is the fact that it can move with the bronze as it shrinks. Also, the people who sinter parts without bindertend to compress these at high pressures. I have no idea how close together/how compact the powder has to be in order to sinter well. Nothing like an experiment to test this though.

jphariot - if you drill a hole in our kiln and add a fan, the gas would still have to go somewhere. Probably quite uncontrolled. For the bronze wax method you really should try and get a good seal around the steel pot. Actually I suspect that with the fan what you'll do is simply increasd the level of oxygen inside the kiln to so that the burning of the gas will take place around the lid of the pot. If your kiln is outdoors and normally used for wax burn-out you may be OK as is - don't know, but I'd certainly invest in a plastic face shield if you haven't already got one, or safety glasses at the very least. Wear these whenever you're within 2 m of your kiln or when playing around with the gas line. Protect your eyes.

I know that CO2 hardening of sand/sodium silicate is used for sand casting. I would think that the bronze powder would be porous enough for this to also work here. Definately worth trying.

have fun but please be careful

[jphariot]

Burkhard,
Thank you for the safety advice. I will get a regulator. But I do remember seeing cooks use co2 to stick down clogged drains. It does blast out!!! So probably really hard to control.
As far as the hole and fan in the kiln goes. Maybe just the hole on top of the kiln is sufficient. Actually, I have NO intention right now of using the Pilato-wax method. I would rather try all these other binders first.
So, I will start with very small jewelry sized parts. If I am using methyl cellulose, how much gas could be created?? Cant be that dangerous in such small amounts.
Is there a way to test the inside of the kiln for gasses?? So that if it works well, and I want to go to larger or more pieces, and more gas is created, I know ahead of time that Yes there are some gases, or no there is nothing to worry about. I will start with the plaster mold. I already prepared a mold. I have powder on its way. I cant imagine there being problems with the sintering bronze shrinking. I realize that it will shrink, but the plaster is filled with fillers and is rather soft. Well see. What I am concerned about is, as the moisture leaves the plaster, will it push steam into the powder and creat pockets on the surface? I am hoping that the steam will take the path of least resistance and go outwards. Also could there be oxygen at the surface where the plaster meets the powdered bronze??? Or is the CO2 effective enough to force that out. The last worry is that as the mold dries it will shrink and sometimes bend, which can open up the parting line. Meaning the molds wont mate and there might be some flashing, or even worse the powder seeps completely out. Other than this, I think it will work.

Daniel, No problem on the additives for freezing. Let me know how your progressing. Also as far as casting bronze. I am actually casting super thin pieces now. You need a vacuum table. It sucks that metal into cracks and anything. Quite amazing. And i poured the dryed bronze powder into a thin silicone mold as a test and it goes into every crevice. Like powder in an hour glass. Much more effective than wax. I use wax for investment, and I dont like it. I inject for some parts. Others I cant, so I use centrifugal force and pressure tanks.
Also I have another idea. What if we mixed a dry polymer powder like polythelene, or something similar. Small amount like 5%. Pour it into silicone molds right. Now bake the whole thing at about 250 350F to sinter the polymer. Now i wonder if the peice can be demolded and placed into the kiln for the real sintering???
What do you all think?
Thanks!!!
John Hariot

[Burkhard]

John - A very, very rough guide would be that for every 10-20 grams of organic matter decomposing into gas you might expect something of the order of 20 liters of gas. It's unlikely that the methyl cellulose in small pieces are a concern. I'm thinking more about what could happen if someone fires a 2-3 kg bronze wax, containing a couple of hundred grams of wax.

Unfortunately I don't have any good advice at this stage about how to deal with large quantities of gas being evolved inside the kiln - except the use of tight fitting lids and the exit gas line. Remember the kiln will be hot and where the gases contact heat and air they will ignite. If you're dealing with small pieces initially anyway then I wouldn't drill holes in your kiln just yet. My only advice is to repeat that I would at least wear safety glasses or preferably a face mask when working near the kiln or if you open the kiln up while it's hot. Start small, observe what's going on before going on to bigger things. Sorry if I sound over-anxious about this part, I don't mean to, but I have no way of knowing who reads these posts and what unexpected things they might do.

With the plaster - can't wait to hear about your results. The air entrapped in the bronze will easily be exchanged by the CO2 blanket in the pot so I don't think this is a problem.

Daniel - glad to hear you're still exploring your freeze casting ideas - keeping fingers crossed. It's a neat idea.

Remember, one experiement beats 100 theories.

When do you all think you'll do some trial firings?

[jphariot]

Burkhard,
Thanks for all the safety info. I like to be safe, and in this case of gases I am not knowledgable. Thats why I use electric equipment. I am aware of electrocution but I can understand it easier and I am not dealing with super high voltage anyways. When I cast Bronze I wear safety glasses and a face shield.
But I hope to get away from that soon.
So are you saying that there is a chance that the methyl cellulose may not even be a problem with gas producion even if I went for large pieces? Again, I h ave no intention of going with the wax. That is my last resort. And I am going to try cow dung before I do that. I dont like using wax right now for investment as it is. Foundry fires are usually start and end with wax.
But I will be trying the dry sand first. I really am impressed with how it seems to easily pour down into silicone molds. Plaster should be no different.
Do you think that the steam caused by the plaster drying might disrupt the powder surface?
I plan on trying this saturday eve. But I am working every day right now. Swamped, and I have to go out and get that co2 regulator. The Steel pot is no problem. But the stainless thin walled tube might be harder to find? I might have to order it. Next day it. If not saturday, next week for sure.
By the way are you in Australia? Lot of inventions going on down there.
Kind Regards,
JOhn Hariot

[Burkhard]

hi John,

With the Me cellulose - rough calculation: using a 2% wt/vol solution and combining with 1 kg of bronze powder - let's say you use 200 ml of the Me cell solution (total guess, you might need more but probably less) then this would be 4 gram of Me cellulose per kg of bronze figure i.e. roughly 4-6 liters (?) of decomposition gases being evolved over a period of 1/2 to 1 hour (I'm making some seriously crude assumptions here). Probably not a problem in a well ventilated area. Problem is that all of this really depends on so many variables that I can't really give you a simple answer. I think the approach you're taking of doing some smaller trial things first and seeing what is happening is exactly the right approach.

The steam disrupting the bronze - no idea really but I guess it will depend on the rate of heating. If you take it slowly enough (maybe hold it at 120C for a while?) then I don't think this will be a prob. I suspect you know more about this than I do.

Yep, down in (not so sunny at the moment) Australia. Sometimes we have to be inventive, takes too long to import stuff from elsewhere.

[DanielUCM]

Harryman and Johan thanks for the additional information on investment casting and the use of vacuum to improve the flow of bronze respectively.

I am planning on doing some experiments on freeze casting as well as the bentonite method during the weekend, but it all depends on whether I get my new kiln tomorrow or not - and whether it functions properly. Like I said my intention was to give some more info on the freeze casting after I had gotten some results to back up the theory but I really want to elaborate on it a bit more. I will also say which additive I believe is the one I will primarily use based on my reading of articles on the subject. Please note that I don’t have any chemistry training beyond senior high school so this is just my take on this (Burkhard and others feel free to step in with comments if there’s some chemical processes or what not that I have misunderstood).

First off, like the bentonite method, freeze casting could prove to be a very simple, inexpensive and non-toxic way of shaping metal. And that’s how I intend to go about it, start with the simplest method and add complexity only when it is necessary to improve the results. Again the main idea is to use the properties of water by mixing a solution of water and additives with bronze powder (or steel powder which I also intend to do) and pour (or through other means insert) this “mud” into a mould. So that is one difference between the bentonite bronze clay and the bronze freeze, one can be kneaded but might be fragile, the other cannot be kneaded but is harder and can hopefully be cast in more demanding shapes. The mould is then put in the freezer and when it has become solid it is put in the suspension powder and brought to heat and thereafter sintered. Another method is to freeze dry the mould and content whereby the water solution sublimates, that is turns to gas straight from solid. Depending on the solution this can give a form which is strong enough in temperatures above freezing not to need the suspension powder. The down part with this second method is that it takes longer time to prepare the moulded item and it might also be necessary to have some expensive equipment to regulate the air pressure. I will primarily test the first method and perhaps a hybrid of the two.

Now to elaborate on the problems with this: First of all the surface tension of the water must be decreased so that the wetting of the metal particles can be improved; secondly the mix must have a viscosity that makes it mouldable without significant pressure; thirdly the metal particles must be evenly dispersed in the solution and kept that way during freezing; that leads to the fourth problem which is that the forming of ice crystals must be kept under control. These problems can be addressed using various additives but during my first tests I plan on primarily using two additives the most interesting of which is glycerol. Glycerol is primarily used for its cryoprotecting properties while at the same time not decreasing the freezing point of water too much, in the right mix. It can also aid in addressing some of the other problems mentioned above, at least to the degree that some sintered pieces are obtainable. I will do some tests using different mixes of powder to solution and additive to water to get an idea which might be the most fruitful.

Ok, now you get a better idea of what I will try to do, hopefully some of the tested pieces will turn out alright so that I can say something more on the additives and mixes. It will be great hearing more about the results of the experiments you guys are doing!

/Daniel S.

[Harryman]

Daniel,

I used to oxidize buckets full of small parts at a time using a simple oxidizing solution. To break the surface tension so the entire part would oxidize evenly, I used to dunk the bucket in a dilute solution of Simple Green and water, followed by a good rinse, then into the oxidizer while still wet. Simple Green works well because it's low foaming, but anything similar would be just as good. As long as you didn't allow the bronze powder to soak for an extended period, it shouldn't really react to it.

Look forward to seeing how it all turns out.

[jphariot]

Burkhard,
Thank you for the gaseous information. I will do small parts so in the worse case situation, we get some small flame. Ive got the feeling that ultimately the best may be something that "burns out" or Gasses out, not something that sinters with the metal, unless we want a hybrid metal ceramic, which in some cases may be really interesting. I am interested in ceramics.
I will do my best to get the remaining equipment and start tests on Saturday.
I have my industrial designer friend who is coming over for these tests. The goal is to be able to produce parts at will. Metal, Resin, Ceramic etc.
I will let you know what happens. Thanks a million.
There are tons of inventions going on in Australia. The Cycclone car motor, and other Hydrogen based generators.(Some of them are most likely pipe dreams), but The most exciting is the "engineair" company with that Air rotary engine that weighs 14 Kilograms I think it is? About the size of a tea kettle. The designer is an Italian who lives in Australia. If you go to youtube you can see a documentary on it. The inventors name is Angelo di pietro I think.
Thanks again!!!!
John H.

Daniel,
With the MUD concept, or Slip if you will, you might want to consider vacuum?? Like in investment? If you need it. If you can do without it, its better. Pressure pots might help a little. Vibration might help too.
Very interesting. Let us know how it goes. Good luck with your new furnace or kiln. I hate waiting for equipment. But its exciting once you get it.
Thanks!

[DanielUCM]

Harryman - Thanks for that tip - sounds like a clever use of 'off the shelf' products: to prepare the powder in the manner you describe instead of mixing it into the solution itself. I'll look around if there is some similar basically non-toxic product available where I live.

John - I think that some vibrating table might be necessary to get the slip (which looks like mud when I have done it with steel powder..) into some shapes. I'll initially try and make it work without having to turn to more expensive equipment than that, although I guess that some form of vacuum function could be improvised?

/Daniel S.

[jphariot]

Daniel,
I dont seee why Vacuum wouldnt work, or help, but as you know with investment casting it is kind of a pain. All the bubbles expand and foam etc.
Could be messy if you dont have a large enough sprue button area, or funnel on top etc. Need room for slip expansion.
Vibration would be easiest. You could even put a palm sander without sand paper underneath as a quick temporary fix. Depends on your design in many cases.
But ceramic makers can do amazing things with slip. Think of fine bone china.
So this might be a great ideal.
Good luck and keep us posted.

Also, Burkhard, I have a question that I keep forgetting to ask. Do you understand what happens during the sintering of the PMC with Methyl Cellulose?
So, what is holding the silver powder together once the Methyl Cellulose burns off? That part doesnt make sense to me. I imagine it must burn off aroun 1000 F and then the powder sinters at around 1200F So how does that work? Do you understand that??
Thanks again,
John Hariot

[Harryman]

Vibration would be simpler than vacuum for sure. I once made a simple vibration table with 4 springs on the corners and a electric motor mounted in the center, underneath. The moter shaft is perpindicular to the table top. Bolt a teeny arm to the shaft with a small weight on the end, vary the weight and arm length to get the vibration you need. I've tried the sander thing, it's OK, but small amplitude and wave length limits its effect.

Burkhard,

How much shrinkage are you getting after sintering? Also, have you noticed a weight difference? With PMC, there's considerable shrinkage and the parts are quite a bit lighter than "solid" sterling.

[enitharmon]

I spoke to a matallergist about the use methy cellulose and di n butylphalate from the PMC mix. It appears it is a 'dirty' method ie leaves lots of carbon in the kiln when fired in an inert atmosphere. Thats why Prof German used the wax as the burn off is combustible outside the kiln.

[jphariot]

Harryman,
Yes, the palm sander is just a quick fix, or quick test. The vibratory table you describe is the ticket. I have built my own tumblers so, boy do I know what messing around with eccentric weights mean. I uses 2 metal discs with holes in them. That way you can adjust the discs. In other words if the discs are at opposite ends, you get no vibration. then slight move one over and you get vibration. Put them in the same place and you get too much.

Enitharmon,
You say this metallurgist said Methyl Cellulose was dirty. Does is also mean that i created explosive gasses? If we place parts in a S. Steel container, it might not be a problem to clean the soot of the inside of the container. Not sure.
What does Burkhard say?? Also I too am interested in the shrinkage rate of The bronze-Bentonite sintering?? I heard pmc might be 10-15% lighter?? That is not much I think. But that must be because its got so much binder and water.
I wonder if you get less weight loss with a dry or dryer powder mix??
Thank Everyone.
Also wha is this "di n butylphalate"? Are you sure its in the pmc? What for and how much?
John Hariot

[Harryman]

John, sounds like you and I have been down the same road, I've built a bunch of vibratory tumblers too. Got sick of burning up motors though and switched to rotaries.

The PMC parts I've weighed are quite a bit lighter than standard Sterling, I'd say your 10 - 15% is a conservative estimate, although I don't know what it truely is. The weight loss wouldn't be much of an issue as long as the metal appeared solid and not porus. Shrinkage would be a bigger deal, especially if it was not uniform, if areas with more mass shrank more than areas with less.

The binder is obviously what is shrinking, so maybe the less porus and water soluble the binder, the less shrinkage before sintering? I'm assuming with PMC anyway, the shrinkage is occuring before the piece is hot enough to sinter.

[DanielUCM]

Concerning the shrinkage of the bentonite mix the third from the last paragraph of the patent says: "The finished part was observed and found to replicate the "green" part originally placed in the oven in shape. The part was measured and found to have shrunk isotropically by 20 per cent. The part appeared uniformly shiney on its exterior surface. Measurement indicated that the part had a density which was 93% of the theoretical density for pure nickel." (Since in the patent nickel is the metal used..)

What do you guys think of what was Marks suggestion, if I remember correctly, of using a foot massage thing to get the vibration? Is that enough for smaller (<40cm high) moulds?

By the way I did get my new kiln today! Its going through the "breaking in" program right now. Tomorrow, Saturday, I hope to get ahold of some of the parts I haven't been able to aquire yet, primarily the co2 tank. The best case scenario is that I can do my first tests tomorrow night - but more realistically on Sunday or Monday.

/Daniel S.

[Burkhard]

Couple of quick bits of info to questions:

Shrinkage: I found that with the bronze clay (bronze powder + 5% bentonite) I get about 9-10 % linear shrinkage when the piece dries and another 10 % linear shrinkage when I sinter the piece. Sintering will (as far as I'm aware) always lead to shrinkage even in the absence of any binders burning out etc. It's just part of the process, the "loose" powder takes up more volume than the sintered material.

I haven't done any density measurements as yet, - might look into how this is done next week. The pieces I've fired so far feel like solid metal, and I can't tell by look or feel that they're anything but solid bronzes.

Di-n-butyl phthalate is a plasticiser, mixed in with plastics such as PVC and all sorts of other plastics to make the plastic flexible. It slowly leaches out or evaporates and this is a major cause of making plastics brittle. I think the oven-hardening "Sculpey" is a mixure of PVC particles, pigments and phthalate. The phthalate evaporates at about 130C, hardening the PVC. The patents describing the PMC do include phthalates as part of the formulation so I suspect that yes the PMC does include this stuff. I have no info as to the density of the final PMC pieces.

I initially thought a similar approach might work for a bronze plasticine mixture. The advantage would be that rather than burning off or decomposing the binder one could simply evaporate the phthalate at about 130C and then ramp up to sintering temp. One quick trial I did, I couldn't easily produce a nicely kneadable bronze plasticine so haven't tried any further. Might be worth some further exploration though.

Had another go at firing a small bronze paper clay head this weekend, as well as a couple of bronze wax "ingots". Firing the wax really is a far messier business than the clay but this time it fired successfully - nice shiny bronze all the way through. Even though the samples were quite small (total probably 150g of bronze wax) quite a lot of soot evolved and flames burning around edge of my pot as well as at the exit gas line.

Surface of the bronze from the wax is just as pitted as the surface of the bronze clay, but the bronze from tha wax may be denser than the clay. I'll have a look at the samples tomorrow or tuesday and try and get some pics up. This time the bronze paper clay didn't show any cracks and dried quite nicely, even though I forced the final drying in the kiln.

Hope people had an enjoyable weekend - Daniel, cool that you got a kiln. Hope you managed to get the other stuff as well. Probably, the most crucial thing in this whole process is the inert atmosphere. I think my early experiments failed because I didn't have a controlled atmosphere. Maybe the book that we can all write will be called "Direct Bronzes for Artists" Subtitle: "The half dozen approaches that will put traditional foundries out of business". Ahh, wishful thinking...maybe.

Dawn - still working on the simple step-by-step booklet! Have you gotten any further? Hope you haven't given up.

[DanielUCM]

Burkhard, that phthalate idea sounds really interesting, too bad it hasn't worked yet. My kiln is working perfectly but I have yet to get the protective atmosphere, all specialist shops were off course closed during the weekends and i went to a number of non-professional stores but none of them had any other gasses than propan and butan. So I will continue with my preparations of the various test-pieces today and hopefully I will get started tomorrow.

Since I have only used a gas-kiln previously I was amazed at how silent and safe electric kilns are! Right now it just stands in my kitchen, in an apartment building, and I have tested it to over 1000 degrees celsius without any significant heat radiating from it. So an electric kiln in combination with non-toxic binders and protective gas should really bring bronze-making into the homes of the artists! With good equipment it is a noticeable investment but there might still be some truth to the suggested sub-title of the future publication :)

/Daniel S.

[jphariot]

Harryman,
Motors burning out on tumblers? It sounds like your tumblers had the motor directly attached? And it was a fast motor? like 3450 rpm?
At this point I have the motors off to the side attached with a belt and pulleys.
I use about 1/4 HP and they run forever. I can take some photos, but I am not sure as to the hassle of loading them on here. My computer can handle downloading any more software. Can I do it without new software???
I had a rotary tumbler. I even built a monster one. Very slow. If you happy with it thats cool, ,but I could email you photos If I cant down load.
Another way is to get a vibratory on ebay. I even built some centrifugal disc tumblers. Fast but not worth it. Cant put too many parts in there, so it defeats the purpose. Took months of work to finally figure that out. But maybe beats spending 10K on a stupid machine.
Anyways thanks for the shrinkage info. Do you think most people would notice that lighter sintered bronze if you didnt say anything???
Thanks.

Also, Burkhard: So if we were to mix Methyl Cellulose without Di N Buthyl Phthalate (what brutally long word) we might not have any luck at all right??
What does it exactly do for the PMC that the Meth Cell. cant do alone??
Another important question: How many hours of use can you get out of your CO2 tank??? If it goes out in a few hours it might seem like its worth using vacuum which can go forever.
Is there any dissadvantage to a vacuum system aside from the initial pain of building a chamber???
I though of building a stainless steel box. Have a lid with a rubber seal , and then just place a electric kiln right in the middle sitting on some bricks. A few holes into the stainless chamber box for the electrical wire and thermocouple and seal the holes with epoxy and thats it.
Now I still dont understand, that if you used a vacuum and you were using methyl cellulose for example and it produced gasses, wouldnt the gasses just come out of the vacuum pump and out into the air. If you vacuum pump is outside it will just go up into the sky. No danger. Right????

Daniel, Is your electric kiln using the off white yellowish firebrick?? Electric is so quite. I dig them. Slower, but way safer than propane, atleast in my mind.
I have some techniques to speed them up if you need to do that? Mine takes about 4 hours to get to 2000F. Thats the tops for mine.
But I built an electric furnace that goes up to 1600 in like 10-15 minutes.
You will want a spare set of elements and make sure the thermocouple wires arent sticking in the furnace too far or they will burn out or melt too often. I now barely have them sticking in I can explain more if you wish.

I did my first test last night. Into the plaster molds. Failure. Got a black piece of charcoal. Oxidized to hell. Not sure why. I will try again this week sometime.
Thanks all,
Johnn Hariot

[Harryman]

John, thanks for the info on your tumblers. We were mounting the motors directly on the vibes and that was the problem.

We used to run 1,000 plus parts in each rotary barrel, Sterling and Bronze. Run them overnight in abrasive and for an hour or so in steel shot the next day. Worked great for our use.

I had several centrifugal disc finishers too for a while, plenty fast, but they were too aggressive, ate too much media and needed a large amount of water recirculated through them to keep the parts clean and cool. Plus if you weren't on top of it and let them run 20 minutes too long, your stuff was toast. They're good for dry media and polishing though.

I'm out of that business these days so I'm tumbler free.

If you used a vacuum that was rated for continuous use you could probably get away with running it throughout a sintering cycle. In my experience with various pumps, they tend to generate a decent amount of heat over time, rotary pumps more than piston ones.

The only disadvantage I see in sucking hot exhaust gasses through a vacuum pump is that it will contaminate the oil and add some heat to the system.

Either way would work, but a flooding system would be easier to build and has a lot less to go wrong/break.

[jphariot]

Harryman,
Wow 1000 parts. Thats great. My tumbers are small. If the rotary works good enought then thats great. Its a simple trouble free system. I spent a good year and a half buildig tumblers. Absolute insanity. I am glad that is past me. Now its the investment casting hell that I am trying to get out of.
Yes, the vacuum I bought a few weeks ago , vacuuming resins, is a welch, and intented for continuous use. I wonder how much HG I need to make the atmosphere in the kiln inert??? Do I have to get high vacuum like 29-30 HG???
I am wondering though how many hours can you get out of a, CO2 Tank before its empty?? Mine is about waist high? (15- 20 Gallon?? not sure)
My piece last night was black like charcoal. And the inside of the steel pot was black, which tells me that I did not have an inert atmosphere.
I think that the plaster was loaded with oxygen and the co2 wasnt able to replace it. Thats my thinking right now. Any thoughts?
Daniel, How is the ICE sintering coming along.
I am totally going to be looking for a way to be able to put the bronze into a silicone mold to get all the undercuts and details and then to remove and sinter. Unless I can cure it easily somehow inside the silicone mold.
Few more thoughts. What about a light cure polymer. Clear silicone molds, and cure with a lamp.
Also what about an I think its called anerobic?? resin. One that cures in the absence of oxygen???
Thanks,
john Hariot

[Harryman]

What kind of plaster are you using? Standard, lost wax casting investment will give off Sulfur(SO) gas as the investment is heated. I'm not sure which compounds and the reaction occuring, but you can smell it after quenching. I'd have to look it up.

There's a new UV cured resin out used in the jewelry industry, very thin (runny) and results in extremely high detail pieces. Cured using clear silicone molds. Here's some info.

http://www.freemanwax.com/HD-brochure.pdf

[Burkhard]

John - my CO2 cylinder is also about waist high, it said it contains 6.8 kg of CO2. If this is true (and I remember my basic gas equations - no guarantees here) then 6.8 kg of CO2 should be about 6800(g)/44 (g/mol) *22 (liters) of gas = 3400 liters. At 200 ml/min that should be about 280 hours of sintering time, or firing for about 5 hours at a time you should be able to fire your kiln about 50 times. If this holds true, and I can refill my tank for AU$45, then that's about AU$1 per firing cycle.

In the PMC the Me cellulose is a long-chain, highly viscous polymer, that acts as a binder and holds everything together. As it dries it acts like a glue to bind the bronze particles together. I think the di-n-butyl phthalate is added to make the whole thing more kneadable. Also the phthalate is not particularly water soluble and may be there to make the PMC stick less to the fingers while forming PMC objects. Yeah, you guessed it - I don't really know.

The UV or light cured adhesives may only cure on the very surface of the bronze. The light won't penetrate far into the object.

With the piece you fired - did you use any binder or was it simply the bronze powder? How big would bronze piece have been? What sort of firing time/temp ramp did you use?

[Burkhard]

This is the little piece that I did over the weekend to try my bronze paper clay. Main aim was to see if the bronze paper clay was relatively easy to mold by hand and whether it would crack like my previous attempts. I was quite pleased with the results - the little head was sculpted directly in the bronze clay, with no intermediate mould-making etc. I could get quite good detail with the bronze paper clay and there didn't seem to be any major cracking on drying.

Took me about an hour to sculpt the head, three days of slow drying and then 5 hours in the kiln. No silicone mould, no wax, no runners and risers, no investment plaster, no cutting off the runners and risers, just a bit of polishing at the end. Final bronze has a nice heavy feel to it. Sweet. I'm starting to like this method. :D



http://i154.photobucket.com/albums/s280/Burkhard_photos/Direct%20Bronze/headinhand.jpg http://i154.photobucket.com/albums/s280/Burkhard_photos/Direct%20Bronze/head1.jpg

[DanielUCM]

Burkhard - That's a really nice piece you have done there, great to see some of your results using your bentonite and paper method!

I have prepared all my pieces for the test fire, just small pieces marked in a manner so I know which mixture is which. I have gotten the gas now but unfortunately the supplier didn't have a suitable regulator so he had to order it but it shouldn't take more than a couple of days. Still annoying that I haven't been able to do this yet.. I have the swagelock but since I don't have the regulator and since the salesman had to look into what kind of tubing he could supply me with I hope that it won't be a hazzle finding the right tubes.

I have used some different mixes and I can already get a sense of which will probably fail and which have the highest likelihood of working. I have also prepared three different bentonite variations.

John - yes its the off-white type of interior in the kiln. Its off the brand Rhode, interior measures 38cm diameter and 40 cm hight. I haven't really pushed it yet so I don't know how fast I can get it to heat up. I'll get back to you if I need some more ideas on how to boost it. The guy who sold it said that I should fire it up carefully the first few times I used it to break it in, so I guess it will take some time before I know how it functions - it is however possible to adjust the computer to warm it up 999 degrees celcius per hour so it should be possible to get a pretty fast heating eventually.

/Daniel

[Harryman]

Wow, looks great Burkhard! Sounds like you're getting the bugs worked out.

[jphariot]

Daniel,
Yes, break in that kiln slowly. I think the elements are the most vulnerable, they say. But on the other hand, Ive put in new elements and cranked it up and didnt have problems. If you want more heat retention a 1" skin of Ceramic fiber board will make a huge difference. Huge.

Harryman,
My investment is plaster and silicosil. (silican flour).
But I was talking to Dr. Srauss this morning. He worked with Dr. German. He teaches powder metallurgy.
He said that my idea of puttin powder into a mold would just end up slouching. Thats what burkhard feared. Well I didnt even get that far.
But he gave me an email to a guy that claims to have a metal clay patent.
I emailed him. Lets see what happens.

Burkhard,
Nice pieces. I think that I am going to stick with the bentonite for now.
There is plenty of clay techniques to draw from and its a good start.
What if you wanted to make copies of that head?? Couldnt you just make cheap thin plaster molds and then push bronze clay into them? Wouldnt they dry quickly that way?? I was thinking of multy part plaster molds for some of my stuff.
The CO2 sounds good. Now just to make double sure. You did use co2 for that head right???
Also, Is the head brittle? Or can it bend a bit. I know you dont want to bend the head, but maybe you have some scrap sample??
And in my first test I did not have a binder in there. I am going to next try the bentonite. Now, why did you add paper? to act as a fiber to keep it from cracking? And what kind of paper? Paper clay I think you said right?

I have a lot of castings to do but i will squeeze in another test soon. But as it looks I will be far behind you. The only thing I may add now is that I will be trying to dry them in multipart plaster molds.
ONE LAST THING. When I spoke to Dr. Strauss this morning. He said that the bronze -wax method really leaves you with a visibly porous part. That if you DONT burnish it, to push the metal and cover the pores, you have a part that looks sand blasted or just plain porous. Is that the case with your samples here? Did you have to burnish it?
Thanks!!
John Hariot

John Hariot

[Burkhard]

Thanks for your kind comments guys.

Yes, the pieces were fired under a CO2 atmosphere. The CO2 works for both the bronze wax and the bronze clay.

I imagine that one could duplicate the pieces by doing a press mould in a dry plaster mould. I haven't tried this yet. My main aim is not really commercial, so I am looking more towards creating individual unique bronze pieces. In fact, what I really want is to produce pieces that would be extremely difficult to produce using traditional silicone mould/wax etc method.

Not sure if the head is brittle, and yep, sorry I'm not going to try and find out with the head :) - that'll have to wait for the next lot of firings.

Interesting that you mention that Strauss said the surface of the bronze wax looks porous. I'd been assuming that I was still doing something not quite right as both my wax and the clay also have a slightly rough/porous surface (estimate about 0.1 mm thick). I used a bit of wet&dry sandpaper to smooth the surface after using a brass brush attached to a drill to shine up the piece. Haven't tried burnishing - sounds like harder work. One of the reasons I did the little head was to see if I could remove the surface roughness without loosing the fine detail of the head. I figured this would be a good test. The porous layer does look like only a surface layer and removing it did not seem to cause me to loose any real details in the head (e.g. around the eyes, eye lids etc)

I'm very curious about the guy with the metal clay - do you have a name? I'd be interested in doing a quick patent search on him. I wonder whether it's R. Wiech's son (the person who invented the bentonite bronze clay)?

[Burkhard]

Forgot to mention the bronze paper clay:

Paper was added to reduce brittleness of the bronze clay and to hopefully improve the ability to add bits of clay together as well as to reduce the amount of cracking when drying.

I used ordinary tissue paper that I weighed out (about 0.7 % wt/vol), added water and then used a metal paint blender attached to a drill to thoroughly mulch up the paper. This was then blended into some of the bronze powder/bentonite (95:5) mix and thoroughly mixed. I used a mortar and pestle to thoroughly grind up the paper with the bronze powder. Then added the rest of the bronze powder/bentonite mix plus a little water to produce a fairly dry, "clay"-like consistency.

[Harryman]

John,

If you have a lot of undercuts, why don't you just make an RTV and pack the clay in?

Burkhard,

If it looks like the pieces need to be burnished in high detailed areas, try using a foredom or pneumatic with a piece of allen wrench in it, or a bur with the teeth polished off. If you bend the shaft of the bur a bit and it's off center, it makes a nice little plainishing hammer. Just give everything that's going to make contact with the piece a high polish. A little lube helps too.

[jphariot]

Burkhard,
If you were to take that sculpted head right after sintering , and place it in a tumbler do you think you could get rid of the porosity? What Strauss was saying was that if its porous all the way through you cant just sand it off or tumble it off. Like cutting into lava rock. You seem to think that the porosity is only surface, which would be excellent news. It looks shiny from the photo
Do you have any shots of it right after sintering??
Good news about the co2. Its the ticket. I think I am sold on it. Thank you for the tissue paper info. I will try it as soon as I can do another test.
Yes I do think its nice to do one offs too. And so quickly. I will be doing that too.
But my priority is evading ......... You guessed it. Investment casting.

Maybe I can do another test later in the week or over the weekend. I will probably be just testing the clay part of it for a few days on my off time, that I really dont have.

Harryman,
I would love to use silicone!!!! But I dont want to wait for the possible weeks for it to properly dry. Unless I could bake it?? in the silicone mold? slowly?? Might crack near the top or something.
I tried mixing a bit of bentonite with alcohol. Seems to mix. Its cracking though.
Burkhard, is there another chemical that we can add to this bentonite that would speed up the drying. Even your 2 days waiting time can be a bit frustrating when youve got a nice piece you want to sinter. Can we replace the water with alcohol?? That would have to be fully evaporated before sintering, I understand. Or maybe the parts can be placed into somekind of drying oven? Convection oven?? How do these companies that make cheap cheap coffee mugs do it? They have to have fast drying times I would imagine. Any thoughts?
Almost forgot. heres the guys name, who might have a clay patent:Bill Struve
I emailed him. Well see if he responds.
John H.
Thanks
John Hariot

[Harryman]

John,

RTV will cure in 12 hours or if you heat it to @ 100 deg F, in just a couple. Various hardnesses available, no mold release needed, stuff pops right out. You do need a vacuum set up, which it sounds like you already have.

Besides silicone there's other rubbers available that cure in under 24 hours as well, some a bit cheaper, but silicone is pretty bombproof.

[jphariot]

Harryman,
Silicone curing is fine. I have excellerators. What I meant was that the clay will take forever to dry in the silicone rubber. Unless we figure something else out?
Let me know if you have any thoughts on that.

Burkhard,
Just got an email from the Bronze clay guy struve. He says that Rio grande might be carrying his stuff. BUt that I can buy it from him at this point.
I am going to call him. Do you want his number or email??? To be honest I wouldnt mind trying some of his stuff but would prefer homemade. Unless his stuff is really impressive. He also has a german silver.
Also, when your tissue paper burns or doesnt burn in the co2 does it produce any dangerous gasses? Do they just seep out of your pot and into the atmosphere without problems?
Ok, I just talked to william (bill) struve. He will be selling his metal clays to rio grande. Exclusive for a while atleast. says you get 25% shrinkage. Doesnt need gas to sinter. It goes into a alumina crucible with activated carbon. Do you understand this??The name of the company is called Metal Adventure Inc.
He says it will be kind of pricey at rio grande. I am on thier evaluation kit list that i might get in august. No samples available now. What do you think???
Also said that there is an australian fellow who is selling a mullite and ??? cant remember dome or cup that you can put into your micro to melt bronze.
I have some info on a guy named reid who was melting metal in a microwave.
Anyways the microwave stuff is cool, but I am going to try the co2 and kiln first. But if you want to look at it, he said you can buy that thing on ebay by searching for "microwave kiln".
Thanks again lads.
John Hariot

[DanielUCM]

Concerning the active coal method - After reading about a method used in West Africa to cast copper, described by Tuck Langland (1999, 9-10) I have had some thoughts of using something that eats up the oxygen. Langland describes how copper is difficult to melt since it oxidises and the casters in West Africa therefore creates a closed system where they have some charcoal in with the metal. The charcoal burns and uses up the oxygen. This should probably work with other substances that are sensitive to oxidation, such as metal powders. I wonder if that's the sort of idea behind Struve's method? I discarded the idea since it seemed either to smoky or since the system would have to be so tight as to make it very difficult to achive but if he has gotten it to work than maybe its another option.

By the way I couldn't help myself to do some tests even though I haven't gotten the gas flowing yet. Just to check if I can get the freeze-casting to hold the powder together during the burning. I took four types of steel powder, from basically iron powder to stainless steel powder. Mixed with a solution with a couple of additives and put it in the freezer for a couple of hours. Thereafter packed it in the aluminium oxid powder and heated it to nearly 1200 degrees celcius. The results was naturally oxidised and black but it was solid all the way through. Basically the same result as when I did the same test using wax so the initial test shows me that freeze casting and wax yield the same result in a regular atmosphere. The difference is that the freeze casting didn't really shrink. The reason probably being the high solids loading and the freezing action which would have made it grow a bit. And since it didn't sinter correctly, only enough to hold it together, it probably stayed bigger than it should be in the correct atmosphere. It was really difficult to drill through the pieces but when I wacked them with my hammer the were smashed to pices and to powder. Just some initial results for you there on the freeze method!

/Daniel

[Harryman]

I've tried covering the surface of the melt with powdered charcoal years ago, it's an old time way to try to keep the molten metal in a reducing atmosphere. It's a bit of a mess, you have to use quite a lot and scrape it and the junk it produces as it burns off to the side as you pour.

If the sintering didn't take so long you could probably do that in your enclosed sintering chamber. I do something like that now casting silver; after it's been poured, it sits in an enclosed chamber with sawdust on it, the sawdust burns slowly, limiting the metals exposure to oxygen. Smells like I'm camping.....

[jphariot]

Gentlemen,
I am not sure how the charcoal will come? In a form of a powder that you pack the clay into??? Not sure. Not sure if it is conducive to making many parts.
But I am on thier sample list for August. We will have to wait and see. But I am kind of starting to wonder if its just going to be one of those things that will work but not as good as gas or vacuum. More intended for the hobbyist who doest want to deal with a tank and regulator etc.
Struve mentioned that we might be able to freeze dry his clay and make it work that way. Daniel, if you get it to work, will you let us in on what your putting in there? Or are you planning on an air tight patent, and a huge contract with Fry metals, with personal jet, mansion, and Rolls Royces?
Putting charcoal on a melt of metal sounds like a mess indeed. I think I would stay with fluxing. Well if your casting in Silicon Bronze then you basically dont have to flux. Well lets hope we can get away from that and make the powder metallurgy work. I hope to be able to run some tests Friday or Weekend.
I will keep you all posted.
Burkhard???? How are things going???????????????
John H

[Burkhard]

Hi guys - up to my neck in budgets, project proposals, etc - no chance to do anything interesting at the moment :( .

Thanks for the burnishing tips Harryman, I'll try to set up something like you suggested.

John - with regard to the porous surface - although the whole piece does contain a few scattered defects and pores (cross-section cut) it mainly looks solid all the way through under a magnifying glass. At the microscopic scale it may of course be very different. The surface does have a matt, sandblasted look, but responds well to emery paper and polish. Can be polished to mirror finish. This porous layer is thin - I suspect that tumbling will get rid of it.

Daniel - great news so far - I'll keep fingers crossed! My main concern initially with the freeze method was whether the whole thing would fall apart as the ice melted. I think its great that this didn't seem to be the case!

John - interesting info on Struve. Couldn't find any patent info on him though. I would imagine that for me it would be too expensive to import bronze clay all the way to Oz unless Struve's clay had some really magical properties.

With regard to the activated carbon - this is often sold in either fine powder or may be pressed into pellets or even tablets. I assume that the method is similar to the method that potters use when trying to get a reducing atmosphere in an electric kiln for producing the beautiful copper red reduction glazes (the red colour comes from copper metal particles being formed in the glaze from copper salts). In this case the glazed pot is placed in a ceramic saggar (i.e. pot with lid) and organic matter such as wood, charcoal or even paper is also placed inside the saggar. Lid is put on and as the temp rises the charcoal burns removing the oxygen and replacing with smoke and CO2. Maybe the bronze clay piece is packed in charcoal powder similar to the way the bronze wax is packed into the alumina powder in the bronze wax method?

Before I got the CO2 cylinder, I started off attempting to do something vaguely similar except that in order to avoid the smoke I placed the bronze wax piece in a pot containing TiO2 powder (to absorb the wax) that had some iron powder mixed into it. I then added another 1cm layer of iron powder ontop of the TiO2. The idea was that the iron would oxidise to iron oxide and help remove any oxygen. I also thought that the wax would slowly burn off, again producing an oxygen free atmosphere inside the pot. The process worked only partially i.e. the outer shell of the piece was sintered but the inside was just copper oxide powder. [By the way, another earlier failed experiment - I tried covering a bronze clay piece in flux (boric acid) in the hope that the molten flux would create an air-tight coating around the piece while firing it in air - no success so far].

The Struve method seems to have worked out the bugs to get it to work properly. However, I could imagine that it would be fairly messy and smelly. The CO2 cylinder seems so much simpler once set up. However, I agree that this may be a good way for people such as Dawn, who want to avoid having to put a gas cylinder etc setup together to fire the bronze clay. If it's messy though, the average hobbyist is not going to want to do this for long, - it'll be interesting to see what come out.

[DanielUCM]

John - As sweet as the mansion and the rolls royce sounds I don't think the freeze casting for art would be a viable patent since I have seen at least two scientific articles where similar methods are used for tool making (not bronze though, only ceramic and steel). I just try not to say too much until I am finished with my first round of tests in case there is some company or something lurking for ideas in this thread :) But after I have been able to get some findings I will continue to report them, and include the details.

Amongst the sample pieces are a couple of bentonite/freeze cast hybrids. I have gotten my regulator today so now I have most stuff - 'unfortunately' we celebrate "midsommar" here in Sweden so I have to go away for some sill (pickled fish) soon.. And plus I need to do some finishing work on a report during the weekend, but the good thing with the methods we are working on is that I can just start it up and let it sinter on its own while I do other things.

/Daniel

[jphariot]

Burkhard,
So, thats great. The Bronze texture is only at the surface. Then a bit of tumbling will take care of it. I have to do that with investment castings anyways. An even consistant texture is fine. But the imperfections you otherwise see were defects you could see in the clay when it was brown right?

As far as the charcoal method, that sounds like it might be a method thats good for the fellow that doesnt want to invest in a tank and gas. But if you had to make 50 pieces might not be worth it Right?? The CO2 Gas it seems, is the ticket.
One other thing is Struve told me his Bronze once sintered is very bendable. Or ductile enough to bend at 90 Degrees, I think he said. Probably doesnt have Ceramic in there then.
I understand it not being practical for you to buy it and ship it to Australia.
I wouldnt mind buying small amounts from the jewelry supply, but large amounts is out of the question. He said that it will be expensive.
So an alternative method is probably best.
He suggested the metal sintering book by German. Any of you have it?
I might get it. I will let you know what happens if I do my second bronze clay test this weekend. Too busy making wax pieces right now.

Daniel,
Better to use the technology for your own products then try to sell the stuff, unless you really want to focus on that. I understand about wanting corporations to stay out of the loop. Personally, I think its cool sharing with individuals. I have developed mold techniques and I share them with my industrial design friends, but make them promise to not share with people involved with large companies. I work alone. I am a designer, and want to make my own stuff. I wouldnt like to work hard and just hand ideas over to corporate executives that have the easy life while I struggle and sacrifice. Work every day etc.
You are from Sweden? Your english is great. How did you learn to write etc.?
How long will you be out of commision with your metal clay?
Enjoy The vacation. I will keep posting my results.
One more question. With the Freeze method. While sintering, do you have to have it surrounded by the alum. Oxide powder? It cant just sit on its own like the Clay right? How much room does that surround powder take. It sounds like it would take quite a bit of room. If I had maybe 25 small 3" statues, it would take quite a big kiln right? More than if they sat alone correct? If so, is there a way around it you think?
And are you freeze drying it?
Thanks
John H.

[enitharmon]

Gentlemen! [and a few ladies]
So many ideas, really exciting to see what is happening. Burkhard you seem to have found a way through the maze. The PMC patent mentioned bentonite changed the colour of the precious metals. How do you find the colour of the bronze? It looks pretty good to me.
I was lucky enough to study lustreware techniques under Alan Peascod in the late 80s early 90s in Sydney. [He was a truly radical thinker, broke all the rules and will be sadly missed.]
It seems some of the techniques might apply here with bronze. Lustreware takes 3 firings. We used a gas fired kiln for the 3rd firing, a glazed ceramic was covered in a mix of silver nitrate and ball clay. The temperature was controlled, ramping up and down to keep temp below the melting point of the glaze. The atmosphere was reduced by reducing the oxygen in the flame. No carbon/coke/charcoal. The kiln was packed on the outside with plastic clay to seal any openings and thus keep out the oxygen. When cooled the sculpture, in my case was scrubbed to take off the ball clay and a beautiful subtle silver/opal type sheen was the result. The silver bonded on the surface with the softened glaze and was not oxidized. The firing took an evening, 3 hours or so, ramping up and down controlling the temp and the colour of the flame.
There might be some information here to work with.

[enitharmon]

Burkhard,
Just a query about your mix,0.7% tissue + bentonite bronze mix. In the patent the bentonite and bronze is mixed prior to the addition of water, is the 0.7% tissue a proportion of this dry mix or was it a wet proportion. It also suggests leaving the mix with water for a week or so for the bentonite to swell and the sugar is added for reducing the viscosity. Did you work with this procedure? Your photo looks like you managed good detail and undercuts. Was there much distortion or did it just shrink like you would expect with clay? The whole process seems much cleaner as there is no burn off. I wonder if the CO2 process could be used for lustreware to give the metalic sheen in an electric kiln. Opens possibilities there too. Exciting!

[Burkhard]

Enitharmon - the weights for the bronze paper clay mix are all dry weight i.e. 95 gram bronze powder, 5 grams bentonite, 0.6-0.7 grams dry tissue paper. I mix the dry bronze powder with the dry bentonite first. In a separate container I mulch the tissue paper with water. I then drain away most of the water from the paper mulch and start adding the bronze powder/bentonite mix. I have found that towards the end I usually need to add a little bit more water, but carefully - a couple of times I was impatient, added too much water and had a paste rather than a stiff clay-like material.

I've used the stuff immediately or left it for a week and didn't find much difference in terms of the way it felt, so I'm not sure if the bentonite really swells a lot over the first few weeks. It could be that this was just one of those "red herrings" (pickled herrings?) thrown into the patent to confuse/obfuscate, or whether it was needed to make the claims in the patents novel over the "prior patent art", or whether it really is useful. Don't know, but so far no dramatic change in the feel of the clay over the first couple of weeks aging.

However, one thing that I'm not sure about yet is the overall shelf-life of the bronze clay. I came across another patent which describes the fact that a problem with water based formulations for metal powders such as copper, steel, iron etc is that the powder reacts with the water to form oxides, giving off hydrogen gas and then can't be used for sintering. The way that these guys got around this issue is to add a small amount of sodium silicate and boric acid. They also added agar to make the metal powder structure self-supporting prior to sintering. The Na silicate and boric acid (or borax) prevented the oxidation reaction from occuring by coating the particles and gave a wet paste with a claimed shelf life of several months.

The colour of the bronze formed from the bronze clay (prior to my attempts at playing with patinas) looks pretty much the same as for the bronze formed from the bronze wax and I think looks similar to the colour of silicon bronze (but I don't have a piece of silicon bronze on hand to compare it directly).

[enitharmon]

Thanks for the details Burkhard, do you think the paste could be put into a plaster mould to capture the detail and slightly shrink for an easy release? Might be interesting for relief sculpture, would possibly allow control of the thickness more easily too. I'm thinking along the lines of a ceramicist here but of course metal doesnt have to be as thick for supporting itself once 'fired', does it.
Enitharmon

[DanielUCM]

Hi guys! I have finally been able to do an experiment using co2 atmosphere! And basically - the freeze casting method worked!! I will get back with pictures and a description. In the following I refer to the method with its working name bronze ice, and I will call the steel version steel ice :), (I think it was John that started using the term ICE?)

I have yet to get a more suitable container and a pipe from the co2 tube to the container which can function with the swagelock. Since it is long-holiday here I could only get ahold of a plumbers chromed copper pipe and stainless-steel sallad/baking bowls in two sizes (one could therefore be used as a lid). All pots I have found appear to be composed of more than stainless steel (during the previous experiment with steel powder I had some metal run out in my kiln causing a mess..) The swagelock I have gotten couldn't be used since the pipe was too big so the container was not even close to air-tight. (As Mark and Burkhard has shown air tight is not necessary but it should probably be a bit tighter than the arrangement I used.) Another caveat is that the pieces had been in the freezer for far too long (i had initially planned to do the experiment last weekend) so they were covered in ice from condense. They therefore got a bit ruined before put in the owen but I just couldn't wait to finish some new pieces.

They pieces came out with a black-green coverage but with a stroke of a file the sweet bronze interior was revealed! Due to the above mentioned problem the pieces look like crap but the purpose of this run was to find out if Bronze Ice was feasibly at all and I think the tests prove that. More tests are necessary to get better results with better looking surfaces etc. The pieces bend before they break. I put one piece on the edge of my anvil and gave it a couple of strokes and it was bent. I will continue with the destruction testing.

John - I packed the pieces (they are about 1-2 centimeters in circumference each) about 1-2 centimeter from eachother. I think that bigger sculptures can also be packed pretty tightly using the Bronze Ice method. I think the distance is more depending on making sure there is enough powder to fill out every part of the sculpture more than on the wicking capacity of the powder, but I have to do more tests to see.

Ok, I'll get back with more information and pictures tonight or early tomorrow!

/Daniel S.

[Burkhard]

Daniel - Fantastic!!! Bet you jumped through the roof when you first saw that it worked! Bronze wax, bronze clay and now bronze ice - cool :D


[Reminder to others - most steel cook-pots have a base that's steel with an aluminium core inside. The aluminium must be removed else it will melt and cause a mess in the kiln. Very expensive cooking pots have a steel clad base with a copper core. A copper core is OK if just sintering bronze, but not OK if you're going for higher temp e.g. for nickel, iron or steel.]

[Daniel - you've probably thought of this already, but if you can't get around to firing the bronze ice samples immediately, then once you've frozen the bronze ice samples, store them in a well sealed plastic bag in the freezer. The condensation ice will form on the outside of the bag leaving the bronze ice samples frost free.]

Again congrats! Looking forward to the pics!

[mark pilato]

Wow , this is all so exciting, its a new age, and you all are making it happen.
put this stuff in the hands of artist and there is nothing stopping it. I cant wait to see some pics
all the best,
Mark

[Harryman]

Congrats Daniel on your success!

Figures it would be a Swede who figures out how to freeze bronze. :D

[DanielUCM]

Yes, I was for sure glad when I saw that it worked! Thank you guys for all the discussions and suggestions on this thread, particular thank to you Mark for sharing with us the Pilato Process and you Burkhard for your pedagogical instructions and suggestions, for instance of using co2.

Now like I said the pieces have a thin black layer and are distorted due to staying too long in the freezer in the wrong environment, and from me yanking them out of the molds and shaving off the excess ice. (I was in a hurry to get them into the kiln since I really wanted to get some results already!) Nevertheless all pieces appear to be solid bronze. In the pictures below you can see the setup of the kiln and an overview of most of the pieces. There is also a picture where you can see the bronze under the surface. I will get better close-ups when my brother takes some pictures with a camera with better macro. I will drill through the pieces and try to smash them with a hammer to see if some mix is particularly weak.

The bronze powder used have 11% tin and 89% copper. If I remember correctly the particle size is <0,045mm. The glycerol already contains 15% water and the ethanol probably contains a few percentages of water (4%?) too. This means that when I write that I added 25wt% glycerol the actual amount of glycerol in the solution is lower.

Since my kiln is new I had a long warmup time and I had the air inlet and outlet open up to 400 degrees c to alow some oxidation of the elements (as the guy who delivered it said I should do at least for the first few uses). Ramped 150 degrees C per hour up until 500 degrees C. From there it increased by 200 degrees C up to 885 degrees. I held it for one hour and let it cool down to around 750 degrees before turning off the gas. The regulator I have don’t let me see millilitres so I can’t say how much co2 gas I used. Wanted to keep it around 200 millilitres per minute but I believe I kept it around 1 litre a minute.

The frozen pieces:
I. Solids loading was intended to be 60vol% for piece I and II but proved far too runny so some water was soaked up leaving something likely more than 80vol% solids loading. To the water solution was added 20wt% glycerol.
II. Same solids loading as I. Glycerol was 25wt%.
III. Solids loading 80 vol%. Glycerol was 20wt%.
IV. Same solids loading as III. Glycerol was 25wt%.
V. Solids loading 80 vol%. 10vol% ethanol.
VI. Solids loading adjusted to get a nice clay-like mix. 20wt%glycerol and 10% etanol
VII. Bentonite and bronze mix plus water with 25wt% glycerol.
VIII. The same mix as that for VI with the addition of a drop of detergent used for hand washing dishes.

In addition to this I froze some bentonite bronze clay without any additives in the water. And also did some bentonite bronze clay without freezing.

The clearest result so far is that if no glycerol or ethanol is added to the water ice crystals affect the entire structure leaving tiny cracks in the piece. Another result is that pieces I, II, IV, V, and VI have the smoothest surfaces and piece VIII is the most distorted - but due to the previously mentioned pre-sintering disturbance of the pieces its difficult to say for sure which mix that produced the best surface. A third result is that number V has the most uniform colour. Another thing is that all pieces with bentonite in them got at least one of the surfaces covered in tiny metal bubbles. I believe that I didn’t mix it properly or didn’t let it ‘ripen’ before being formed. And the bentonite I used was perhaps a bit coarse.

As I interpret the results so far an addition of 25wt% of glycerol (which has already bonded 15(vol?)% water) or 20wt% glycerol and 10 vol% ethanol appear to be a good way to go. Adding off the shelf detergent to get smaller surface tension might not be so good but that result could be sceved since I don’t remember how bad I manhandled the piece pre-sintering. A better way might be to do as Harryman suggested and just wash the powder in some detergent solution or to get the real deal surfactant (if necessary, I think it depends on the characteristics of the powder). As regards the solids loading I think that the best way is to add a little of the water-mix at a time until the proper mix is attained, I believe that the necessary amount of water depends on the size and type of the solids loading. The bronze powder very suddenly stops mixing with the water and separates from it so its really necessary to add a little at a time.

Although I had problems with the bentonite bronze clay pieces it seems that a hybrid ice-clay method should be possible for the cases when its necessary to shape pieces by hand but to also avoid the brittleness of when they are drying.

So far when inspecting the bronze there appear to be no obvious porosity but the deeper inspections might give another story. I will get back with some more pictures from when I have drilled through and beaten the pieces. But like I said in the previous post the piece which I have hammered at so far bent rather than break.

I will do a mould of a sculpture now and cast a couple of mixes of the bronze ice to see what happens when it is used for more elaborate shapes. Now that will be really interesting to see if there will be any serious distortions and then to avoid them! I will try to upgrade to a serious pot and a better pipe that can fit the swagelock, that should give better looking surfaces.

/Daniel S.

[DanielUCM]

Ok, here is a close-up of a hybrid piece with bentonite but without any additives to the water. The surface of this piece was not ruined during the pre-sintering phase as most of the other pieces (see my comments above for information why they were ruffened up before sintering) so the cracks that you can see where it has been brushed clean is the result of ice crystals. Just to illustrate why the right water solution is so important.

/Daniel S.

[mark pilato]

Hi all,
lets all get together for a conference call, maybe we "all" can talk via phone, I think I can answer a lot of your questions and get this working for you, remember I have done many, many pieces. I have even slush cast a 14" piece, way to difficult to try to explain on this thread, but very easy by phone, my dyslexia makes this stuff hard to write down, takes me 5 times as long as you, and these days I just don't have the time. I know why your pieces are black, I know why you are getting cracks, and I know and most of all I know how to make it work. The mix, the kiln, the temp's, and most of all how to do it in easy to understand terms, I want everyone to be able to cast a piece in their home without all the expense. My info is free, so lets do it, lets get this up and running.
all the best,
Mark

[DanielUCM]

Mark - Great idea with a conference call! The problem, as Berkhard indicated previously, is that we are in different time zones spread out from USA, through Sweden, to Australia.

Concerning the cracks: The latest picture I posted was just to show what happens if NO cryoprotecting solution is used in the water mix when freeze casting - so I had no problem with cracks in the pieces that were cast using more correct mixes. It was just to underline that the mix is important. The major crack that can be seen in one of the other pieces (in the picture of all pieces) occured before the sintering. In fact the piece was split in two during demolding (of the reasons exlained earlier) but during the sintering they were joined again. So cracks has not been a problem.

The blackened surface however is something that I need to solve, but I got it on all pieces even the bentonite so its not due to the freeze casting method. I belive its because my set up is still letting to much oxygen in, but I'm not sure. Would be nice to hear what you have to say about it Mark, so let us think about that conference call. And you Burkhard, have you encountered that problem?

Ok, I'll get back when I have done some destructive testing and have more pictures. I might have something to say about the shrinkage of the pieces also.

/Daniel S.

[Harryman]

Mark, thanks for the offer for the conference call. As Daniel mentioned it might be hard to get everyone together to do it, but perhaps if at least one of us could coordinate a time, they could then act as your "PA", take notes and post the info for all to see.

They could also bring you coffee and donuts like a good PA should. :rolleyes:

I'm pretty flexible with times, so I could probably work with most peoples schedules for a conference call if you all want to try to set something up.

Daniel, Sounds like you still had a oxidizing atmosphere if your pieces are black, maybe a better seal on your system will help the CO2 keep the pieces flooded. I would guess that the CO2 helped though because it was only the exterior that was oxidized, so you're probably close.

If you're going to use soap/detergent in your mix, be careful, many have some type of ammonia in them which will oxidize your bronze over time. There's other stuff too which probably isn't great to the metal as it burns up, to be safe, I'd just use it to wet your powder, then rinse away.

[enitharmon]

Mark, a conference call sounds good. I'm in the UK time zone so links with Sydney would be best on the weekend [ie 22.00 Saturday UK = 7.00 Sunday Sydney] I'm about to buy a kiln and have sorted out contacts for the fabrication of a stainless steel chamber. Looking through the details of your processs on the thread there are steps which for me need clarification. So I have lots of questions. I am itching to go but don't want the neighbours screaming 'fire!' if I can avoid it.
Freezing bronze, Daniel, bound by fire and ice...there in lies the spirit of the 'creative'.

[mark pilato]

You pick the time and day and i will be here.
just let me know when - my time. Also lets try to get as many people on line as we can so I just have to answer once, lets give it two weeks .
all the best,
Mark

[jphariot]

Daniel,
Excellent work. I may have used the term ICE. A few years ago I was talking to some lads that had a 3D prototype machine that made parts out of ICE. Then they would be used for investment casting. It seemed to have enough problems and not offer enough benefits for me to dive head first into it.
But freezing or freeze drying metal powder and a Binder is a whole different deal.
It was on my list, but only after I got more confortable with simpler methods.
But my hat goes off to you. I feel ashamed that I was not able to do any tests this weekend. But I was spending all my time with investment castings.
But I have been ordering binders. I have 3 more on the way. I should also receive my regulator tomorrow. So I will be joining you all with tests.
Still one or two questions. Sorry to take you many steps back. When Sintering are you forced to to have the part held in a surrounding powder like the wax method? And did you have any detectable dangerous gasses coming out from you part during sintering?
Also did you have to download that extra piece of software in order to post the images?
I need to run a few bentonite tests first. Get a feel for it. Then depending upon my results I may be jumping into your frozen world. It would be great if I can find some ways to help in the cause. My mind needs to convert over. Its still way too stuck in developing alloys that melt. I have recently developed a white metal that can be cast into silicon molds and yet be as strong as brass.
I still think that I will still be casting metals, but ONLY low melting metals that cast into silicone. Thats easy. But If I never cast another bronze or Silver casting in my life I will be delighted. Hate it. So my hate is a passion I will hopefully be able to channel into helping develop this.
I will post more later this week or over the weekend after My tests. Sorry if they will be a bit old school and behind.
Thanks,
John Hariot

[DanielUCM]

"So I will be joining you all with tests.
Still one or two questions. Sorry to take you many steps back. When Sintering are you forced to to have the part held in a surrounding powder like the wax method? And did you have any detectable dangerous gasses coming out from you part during sintering?"


Great that you are gearing up and joining! Will be interesting to hear about your results. I suspended the parts in the aluminiumoxide powder for this test. But when my brother and I did some initial tests of the castability of the water and metal powder mix (using steel powder) into silicone moulds some months ago we found that some rudimentary freeze drying actually resulted in a piece that held together in room temperature using mainly glycerol as the additive. (Maybe the tap water here contains something that aided in this process, will try using destilled as well as tap water for my next attempt.) When I say held together I mean that it was basically as brittle as the bentonite pieces when they were dried, but with the benefit that they can be demolded in the frozen state (and demolding is the major problem when dealing with brittle pieces). So we'll have to wait and see if the powder suspension can be ignored for some of the types of sculptures we want to make. It is off course possible to add some binder but I want to make sure that the method is as non-toxic as possible and that a mix can be used for more than one occasion over a couple of days (so that it don't hardens when sitting in the mixing pot)

Concerning the gasses. The reason the test pieces are so small is that I wanted to make certain that any dangerous gasses would only develop in very small amounts. The set-up is right by the balcony/garden exit and by the kitchen stove-fan so I had good ventilation. I could not sense any strange smell and I believe that it should basically be safe, but perhaps Berkhard has something to say concerning the chemistry of glycerol and ethanol in co2 atmosphere? My main worry when I did this was using the co2 (I've never used it before) and that my temporary pipe is covered in chrome. I've heard that chrome could be very toxic but I figured that it would be ok in such low temperatures, and it appears it was.

"Also did you have to download that extra piece of software in order to post the images?"

I managed not to use photobucket or similar. I opened the picture in photoshop, selected 'image' and 'image size', and changed the resolution to 72 pixles per inch. Thereafter I used the 'save for the web' saving option. In there it is possible to set the quality of the picture so it falls below the required maximum size to be allowed to upload it. Don't know how to do this using some other program though..

I need to run a few bentonite tests first. Get a feel for it. Then depending upon my results I may be jumping into your frozen world. It would be great if I can find some ways to help in the cause. My mind needs to convert over. Its still way too stuck in developing alloys that melt. I have recently developed a white metal that can be cast into silicon molds and yet be as strong as brass.

Yeah, I think we are going to be using different types of methods depending on what we are sculpturing/designing and depending on whether we are creating directly or using moulds. Bronze clay great for forming with one's hands, Bronze ice good when using moulds and when a basically non-toxic method is wanted, and Bronze wax when one wants to continue making even more demanding forms after demoulding (or when carving a piece). Possibly a hybrid between Bronze clay and Bronze ice would work for some pieces. I think that being able to choose between these processes leads to the means being subjected to the will of the artist rather than the other way around.

By the way, that white metal sounds interesting.

/Daniel S.

[DanielUCM]

I am itching to go but don't want the neighbours screaming 'fire!' if I can avoid it.
Yeah, I've been closing the shades to my window when I've been doing this, don't want any unneccesary attention. And when I had gotten my co2 gas canister I hurried from the car to my flat so that noone would have time to react if believing it was flammable gas..

Freezing bronze, Daniel, bound by fire and ice...there in lies the spirit of the 'creative'.

That's a quote I have to steal when I have set up a homepage for my stuff!!

/Daniel S.

[jphariot]

Daniel,
Ethanol being used as an auto fuel would concern me a bit unless I knew it had time to evaporate prior to sintering?? Glycerol?? Lets see what Burkhard says???
Demolding is critical, I see. Yes, I think having to surround the part in a powder while sintering is a deterent to me. Not a major one, but enough of one at this point. Maybe a highbrid is really desirable then.
Freeze drying. I have a vacuum chamber and Pressure pots. What else do I need to freeze dry. I know little about it. I will read up on it. But what do you know that you can share? Bill Struve mentioned that it might work well with his clay.
Have you yet tried just pouring a powder into a silicone mold? It fills every crevice it seems. How is your clay going into molds? Do you have to press it into the halves of the mold and then join them?? That would seem to be so innacurate. A slip might work nicely.
Photoshop!!!!!!??? Perfect. I have photoshop. I will try that as a test soon.
Thanks. i dont want to download new software. My computer has enough.
Keep up the good work.
John H.

[enitharmon]

Daniel, you are welcome to quote, did you say you were in Sweden?
Here are the sincronized times for Saturday 7th July and Sydney 8th July.
Sweden 23.00
England 22.00
New York 17.00
Colorado 15.00
Los Angeles 14.00
Sydney 7.00
Is this OK for everyone?

[DanielUCM]

Now I have done some more thorough testing of the bronze ice and the hybrid bronze ice/bronze clay.

All of the bronze ice samples are really hard, both to drill through and when bending over the anvil with a hammer. And that is good news. Most samples bent instead of break, and since they are so small and since they got work hardened with the hammering I didn't manage to bend them much. It was only one sample that I managed to hammer to a 90 degree angle (and beyond after that), number VIII. The hammering might have caused it to be so hard as to break rather then bend, but due to the look of the cut I suspect it was the particular formula in that piece (it included some off the sheld detergent, see previous post) that made it weak.

In the holes I drilled into the samples I couldn't see any patterns of porosity with my bare eye. However, all of the tested pieces had some form of defect in them in the form of a small hole or a small crack. By the looks of them they are likely the interior eveidence of me manhandling the pices during de-moulding prior to sintering. (The reason for which, as I have said before, was that they were left in the freezer for too long so iced formed all around the pieces and moulds. And I was so in a hurry that I just ripped them out).

As I suspected with those that contained bentonite, since at least one of the surfaces of all bentonite pieces were 'bubbly', I did something wrong when mixing it, or the bentonite powder size I got is not really suitable for this. One ice/clay hybrid and one clay piece had not sintered properly inside and were easily smashed.

In conclusion the results are in general strong bronze pieces but due to the badly prepared pieces I'm not able to draw too many conclusions except that I will definitely continue my experiments. I intend sinter some new, more sculpture-looking, samples tomorrow. I will leave the hybrid between bronze ice and bentonite bronze clay for now until I have time to look into it some more.

As for the phone conference I will be off for vacation from late Friday or early Saturday. I'll be back to my telephone during some days in July, and will try to gain access to internet as often as possible. Harryman, as I believed you indicated, perhaps its possible for those who can make it for a phone conference to report back to the thread? Even though Burkhard managed to analyse the entire process and report it here, it sounds like Mark could have some more important points to share or emphasise.

/Daniel S.

[enitharmon]

I came across a very stretchy silicon mould. Rebound 25 from Smoothon, American company [it can also cast low melt metals]. This might help in the demoulding of the more fragile pieces but of course I don't know how it fares freezing.
Referring to the paper clay, I have used a kitchen blender to mix paper pulp with water for paper making and it works fine if the pieces of paper [in my case watercolour paper] are torn up.

[DanielUCM]

All right guys! Now I have two pieces for you now with details. The first picture of the first piece is of the original oil clay of the female figure. Its a real miniature only 8 centimeters high. I did a mould, took 24 hours. I skipped the mother mould to save time so the resulting freeze cast was distorted, but since the purpose was just to see the feasibility of making sculptures that's not really important at this stage. I was running out of bronze so I just filled the mould partly. This time I didn't let it freeze so long time so I lost I couple of details (part of the chin for instance) to premature melting. (I am leaving for vacation today so to make this on time it has been down to saving hours..) I used a mix of water plus 13% of the waters weight in ethanol. So the second picture shows it straight from the kiln and the third after going over it with a piece of sandpaper.

The second sculpture-fragment is a part of a bigger figure but to save bronze I just did the head and the shoulder area. The first picture is straight from the kiln and the second is after a minute of sandpaper work. I used a mix of water plus 25% of the waters weight in glycerol (glycerol already containing some 15% water).

The result is that the female piece using ethanol has a really good surface straight from the kiln (better than I get with normal casting..) which would only need the burnishing that you have talked about earlier to make it smooth (if that is wanted). The male figure using glycerol has a surface which has a lot of minor 'bumps' on it. I need to look into why that is a bit more but the tentative conclusion is that for the powder I'm using ethanol has worked the best. With the slow warm up time I use (plus I let the air out through the ventilation hole up to some 150 celcius) there appears to be no danger to using ethanol so far. I shut the vents earlier than last time and had co2 flowing basically from start and until the kiln had cooled to around 500 celcius. So despite my still pretty rudimentary pipe and container I was able to get a good surface on the female figure.

The problem that remains is to continue figuring out which mix works best with which type of powder and which freezing times that are best with which temps. The figures are to fragile right now even in the frozen state so there is a lot of work left to do. I just want to avoid mixing in to many chemicals and binders since I want to keep it non-toxic and I want the resulting bronze to be very pure and compact.

I have tried to minimase shrinkage by having a high solids loading. Just to give you an indea of the shrinkage. The male head was around 40mm high and 27mm wide before sintering and 36mm high and 25mm wide after sintering so as far as I can see the shrinkage has been uniform! I will take better measurements for my next attempt. Just need to stock up on the bronze powder..

Now, I can leave for my vacation! I will try to check back on this thread as often as I get ahold of an internet connection, I'm just glad I was able to give you some more info before I leave.

Best wishes

Daniel S.

[jphariot]

Enitharmon,
I would be fine with the July 7th Phone time, if your up for including me.
But it would be even more powerful if Daniel could be present. But I will leave it up to you gentlemen to decide. Also, Burkhard is key.
Also, you mentioned Smooth on silicone. I have tons of experience casting metals into silicone. That has been my main thing for about 5 years now.
As far as freezing, I dont know, but for heat Platinums are the best. As far as RTV silicone goes. The actual best is Vulcanized. But RTV is fine and easier to use really. I would even guess that Platinum would be better for freezing. It is a way superior product over the tin based. SMooth-On is fine, but since your going to order it from the states, I would highly recomend the company I deal with. The prices are better and product is better. Plus they are very helpful.
They are called silpak. If your interested, I can give you the number. Also, I can help you with any questions you have regarding silicone. I make molds every other day, just about.
Daniel,
Excellent work, once again. Sorry I have been away for a few days. Its ironic, but I have been doing some investment casting again.
And as I was making the waxes, I kept thinking about ways to make clays, slips, or powders etc. I now have my regulator and hose in place. All I need is to fill the co2 tank and make some parts. If I dont go to the local pub for a pint of ale tonight, I may start modeling some parts. If not, it should be in the days that follow.
Now I ordered 2 binders that are on the way. They are both soluble in a solvent but also thermoforms. So I plan on trying both methods. The crazier, but more interesting idea, is to blend both metal powder and binder and pour into a silicone mold dry. Then bake. Then sineter. Its a long shot really, but I think that what they do with Metal injection molding isnt too far away. Not sure what will happen when that binder is sintered? Somekind of gas I imagine. What do you lads think of the idea of using sodium silicate as a binder and then pusing co2 into the mold? I dont know if that co2 will get to the whole part. They use that with sand, but its not nearly as fine as the powder. So it might just hit the surface or wherever its entering the silicone mold but not farther.
I am with you Daniel, as far as keeping it as non toxic as possible. That is key.
I may need to be doing this inside a kitchen, garage, or office at some point. Not sure if I will have an official shop before I embark on this. But even then, its best to keep things as non toxic as possible.
One question: The scupture on the left? is that the one with ethanol? It looks almost un sintered. It looks CLEAN!!!!!! Good job. I am inspired.
Let me make sure I have it straight. In the Wax method the alum. Oxide surrounds the part, to absorb the wax.
But in the freeze method, why are you surrounding it? Is it to help the part hold its shape untill sintered? Do you think that once the ethanol is burned away the part would fall apart??
With the bentonite, Its easy to see. Both powders sinter together.
Thats what I dont understand about the PMC. How does the silver powder stay together once the methyl cellulose had burned off? Or does it sinter before it burns off? That doesnt sound right.
Thanks all!
John Hariot

[DanielUCM]

John - The sculpture on the left is the one with ethanol. And just to clarify, the photo on the far left is just the clay original for comparison, and furthermore I ran out of bronze so the mould was not fully filled, and like I said since I didn't have a mother mould it got a bit distorted. So I will make a mother mould and try it again later.

Like I said there are still many problems with this method but I think that its starting to be possible to make acceptable pieces.

I use the aluminium powder as support for the pieces for when the water melts. Otherwise they risk falling apart. When doing some experiments with freeze casting steel powder in silicone moulds a few months ago me and my brother managed to get pieces that were somewhat freeze dryed with the glycerol acting as a binder so it would probably have been possible to sinter without the powder. I don't know if it was just a freak occurence due to the right temp and humidity in the particular freezer we used or if we will be able to do it again. Otherwise to make real freeze dryed pieces they need to be put in vacuum (don't remember the preassure) while remaining frozen. I will continue looking into the possibilities of making some form of 'pseudo'-freeze drying.

Nice to hear that you will do experiments using some binders, sounds like a great method if you are able to pre-heat the mix in silicon moulds! Keep us updated on that.

/Daniel

[jphariot]

Daniel,
As far as the statue 2nd from left that was sintered. All the dark spots, is that pits or just dark spots? Or should I ask, is the texture on the sintered statue close to as smooth as the clay one on the far left? It is hard to tell, even if I zoom in.
Yes, I am still not sure what method, I am going to sink my teeth into. I need to kind of play with it for a day or two and sleep on it and then i will latch onto a direction. For atleas a while, and then maybe change directions, depending on results and what I can imagine to work.
When you filled your silicone molds with the powder and ethanol. Did you fill one half and then the other and join? Or were you able to pour it in a gate or hole somehow? I think or imagine your mix was like a hard dry clay right? Kind of crumbly where it needed a bit of packing? Not very wet like ceramic clay?
I still think that a dry powder would be the easiest to pour into molds. It would go into every crevice, I think. The question is HOW can we bind it.
What about some kind of binder, brushed or sprayed into the silicone mold prior to pouring? These are loose ideas. I need to "experience" a few days or weeks of getting a feel for it. Then the ideas come.
What do you think?
Burkhard, any experiments lately??
Thanks,
John Hariot

[enitharmon]

thanks John, I'd like to know more about the silicon you use. Rebound 25 is expensive, though it is a platinum silicon and does go into small crevices. I will contact you about the phone conference by Friday.
Daniel, did you apply pressure to the feedstock when it was in the mould, I was also wondering what the surface was like, for this the size of the particles seems important. Was expansion of water a problem when it froze?

[DanielUCM]

I managed to get ahold of an internet connection again!


As far as the statue 2nd from left that was sintered. All the dark spots, is that pits or just dark spots? Or should I ask, is the texture on the sintered statue close to as smooth as the clay one on the far left? It is hard to tell, even if I zoom in.

The dark spots are mostly just dark spots since the piece was left with varying levels of darkness from the kiln. I just took a sandpaper (made for wood, all I had home) and draw it over the surface to get some highlights on the high points. However, the sintered sculpture does not have as smooth texture as the clay original since there is some porosity in the surface and some minor unintended low points. The porosity will probably be reduced to the level that Burkhard and others have seen when I get a tighther pot and connection between pot and tubing. The small unintended low points are likely the result of the mix, which likely need some dispersant (aids in making the mix more homegenous) and/or surfactant (reduces surface tension). Nevertheless it's the best surface I have achieved so far with the Bronze ice method (after two burns and various formulas) but there's still a lot of work to be done to get it up to a level where minimum post-sintering work is needed. Unlike casting where so small details as fingerprints can be visible, but where the downside is that there might be alot of defects on the surface etc., with this method such small details are not yet preserved but on the other hand there are none of the defects that I have seen during normal casting. I actually already prefer this method to normal casting!


When you filled your silicone molds with the powder and ethanol. Did you fill one half and then the other and join? Or were you able to pour it in a gate or hole somehow? I think or imagine your mix was like a hard dry clay right? Kind of crumbly where it needed a bit of packing? Not very wet like ceramic clay?
I still think that a dry powder would be the easiest to pour into molds. It would go into every crevice, I think. The question is HOW can we bind it.
What about some kind of binder, brushed or sprayed into the silicone mold prior to pouring?

The moulds was not so demanding for these pieces and I did cast them solid and not hollow. This means I was able to simply pour the mix, through the torso area and through the arms. The arms are really thin so the mix flows pretty well the way I did it. I mixed it with so much water that it turned into a slip. Due to some problems with attraction between particles (don't remember the chemical/physical name, Van der Vaal binding??) the particles set together really quickly and separate from the water (when the mix is a slip) and turn into a hard clay, hence the need for a dispersent substance. What I have done is that I just give the slip a good stirr before pouring and then it flows just fine. When doing a solid cast this is okay since the bronze settles and the water and ethanol solution can just be pored out (and more of the slip added if neccessary, etc.). Thereafter into the freezer. This leaves a freeze cast with a high level of solid particles. When making a hollow cast I have some ideas how to go about it and I will keep you posted when I have returned home from my vacation. I can say that as it is now the mix fills up simpler moulds well. To do the hollw casts its probaly necessary to get a mix where the particles are better dispersed in the water.

Enitharmon - I did not apply any pressure when I did the above. Since I have yet to sinter more coarse powder (my steel powder is coarser but the pipe I have as a temporary solution cannot cope with the temperature) I'm not quite sure of the relation between powder size and surface but I think it could be assumed that it will be affected. Expansion of the water was not a problem that I noted for these tests since the solids loading was so high (and since ethanol or glycerol was added).

I can't wait until I get a hold of more bronze powder and return to my kiln, really want to improve this method.

/Daniel S.

[jphariot]

Enitharmon,
The company is Silpak. They are the most reasonable in price in the states.
And they are good too. Actually, if your only freezing and not casting metals, you might be able to use a economical tin based silicone. They have a product called econosil. comes in a gallon only. Now you can save further, by adding silica flour after you mix the catalyst. Use it as a filler. Gain volume. But it does make the rubber harder. So you can first add it plain, then add some silica flour and pour more. Silpak.com If you email them or call them ask for Jerry. Hes been helping me for years.

Daniel
I have another idea. What about; when you pull the Iced Bronze out of the freezer, you dip it into a hydrastone or plaster slurry then place it in the refrigerator. Gypsum will set in the frige. This can take the place of the Alum Oxide sand. Would that be advantageous? Certainly more space saving. You can get gypsum to set in a few minutes with accelerators.
Also, I am trying something else. It worked!! Well it "SET" and I was able to demold, but I did not sinter yet. You lads are going to think I am crazy, but I am focusing on the casting and setting part right now. Plus ive been too busy to go fill my co2 tank. I do this when i am waiting for something to cool or heat etc.
This is what I did. Instead of bentonite. Refractory. It doesnt need to dry. It sets. It should behave the same way as bentonite, in the sense that its high temp, and wont fall apart during sintering. It will only harden. I have accelerators for it and can get faster ones I think. I will sinter it later in the week or next week at worst, i think.
I have a host of other ideas in my head, but they are not fully thought out and scattered. I will be giving you more ideas soon.
What do you think of the refractory idea?
John Hariot

[enitharmon]

Thanks Daniel, I'm starting to visualise the way it works.
Thanks for the contact too John. I've been making some mini moulds but need to get the powder, still a problem here in the UK but I hope to solve some of these problems cause I'll meet up with a metallurgist tomorrow, if the rain here in England ever stops. My cat is looking at me, 3" from my face while I type, she's sick of it too! [At least we aren't flooded so who am I to complain]

[enitharmon]

Guys if you look at your messages you have the numbers time and PIN. Contact me if you need more information, hope it works out.

[jphariot]

Enitharmon,
That is funny you mention rain, because its so hot and dry here right now.
I was looking at a picture of an old british sportscar I like, and its in the rain, and boy what I wouldnt give for some good rain. My family is from Europe and I spent a little time in Cambridge and boy that rain sounds good. I live in the hottest spot in L.A. And I am casting metal and wax in a small room with no A.C. Send me some of that rain please.

Back to business!! What do you mean by numbers time and pin??
I am trying some slurry casting tonight. First one looks pretty good. Only two small bubbles, or holes. Better than a wax casting really. I have refractory in the mix, so I am not sure how long it will take to set in the freezer. It needs to stay there until it sets. I am thinking about freeze drying. Is there a way to make an inexpensive homemade set up?? Daniel,, do you know? Burkhard?
I read some info on it the other night, but need to read more. Not sure it made perfect sense really.
I also JUST recieved some sodium silicate. I am thinking of using that as a slurry to dip a frozen part into. You would be surprised at how fast co2 will make sod. silicate set. Seconds. Maybe also can be used as a binder???
Not sure. Any thoughts?
Thanks lads.
John Hariot

[enitharmon]

Hi John, still raining here....scroll to the top of the page right hand side you should see 'welcome jphariot' and private messages. Open the private message and you'll see a message from me with the details for the phone conference. Call the number at the time and enter the pin on your phone key pad and we can hopefully chat to Mark. I haven't done this before so hope it works.

Also guys, my metallurgist friend WARNED strongly against the use of CO2 gas because the metal hunts for an oxgen atom and leaves carbon monoxide behind...DANGER. :(

[jphariot]

Enitharmon,
I did not check this site again untill just now. It seems like the conference was at 2:00 in the afternoon my time here in L.A. Sorry! How did it go??
Your friend who said that co2 will produce Carbon Monxide. Is he certain of this?
Does Burkhard have any thoughts on this? Does he do Powder Metallurgy. If he does then it would make sense to know. And maybe thats why they use other gasses in the industry. If co2 is no good then I think I am going to go to vacuum. Actually, I am doing this outside, so for now it wont matter to me, if theres Carb. Monoxide. Long term, i want to do this indoors.
I tried freezing a bronze slip and then dipping it in a cold gypsum slurry. Melted some of the iced bronze part. The freezer was set as cold as possible. -5F.
Thinking, thinking. Freeze drying seems kind of tricky from what I am reading.
Any thoughts? I have a vacuum pump and a tank, with a heat source under the tank. Not sure about all the specifics.
Any thoughts gentlemen?
Daniel, are you able to place your frozen Ethanol-bronze Iced part into the Alum. Oxide powder fast enough before it is able to start to melt?
Thanks,
John H.
Thanks,
John Hariot

[enitharmon]

Hi John,
Absolutely sure! He's a Professor of Materials.
The conference didn't work due to PIN problems but I chatted to Mark and will post when I get time to write it up though nearly all info is already on this thread. Specific proportions are also 'artists' feel ' as the direct formulae aren't written down.....these are with some patents somewhere... so some degree of experimenting will be needed.
Some sun here...but I know what endless heat of summer is from Sydney so feel for you without AC.

[mark pilato]

That dam artist feel, feel stuff, if only they could write it down, a lesson for the scientist in you, sometimes what seems impossible has the simplest solution, and sometimes a crock pot, a foot massager, a stainless steal garbage can, a salvaged vacuum furnace and a scut kiln can do the trick. And yes mixing the bronze powder works by eye, the same way you mix plaster, until islands form, then when its up to temp skim off the top. Also for slush casting use the
nitrogen to freeze the slurry just after you slush cast, this instantly solidifies it. I took it straight from the hose and it worked beautifully I sintered a 16" owl 1/8 inch thick this way and I am pretty sure the first in the history of art, not bad for a little artist feel, the scientist were working on that one for a very long time, Me I just looked around the room and saw the tanks and knew what I had to do. Don't get me wrong nothing works better then a scientist and an artist, but its us artist that have the most to gain with this one, and yes we can be a little sloppy getting the dirty work done. Rand I know your listening, just jot down some numbers for these chaps , so they can get it rolling. They will bring your vision to the front of the art world taking it to new ground. I'll call you next week to see if you can give them a little peek. Rand, you know whats up, you are the master of the field, please don't wait until you are retired to share. There is sufficient fuel for the fire and its hot-hot-hot. Give them some of the good stuff, the same stuff you gave me.
All the best,
your freind,
Mark

[DanielUCM]

Allright, got a hold of my connection for a few hours now before going away again.

I have another idea. What about; when you pull the Iced Bronze out of the freezer, you dip it into a hydrastone or plaster slurry then place it in the refrigerator. Gypsum will set in the frige. This can take the place of the Alum Oxide sand. Would that be advantageous? Certainly more space saving. You can get gypsum to set in a few minutes with accelerators.

I think that the problem with this could be what has been mentioned above with the gypsum/plaster not flexible enough to 'shrink' with the bronze, in this case the bronze ice, during melting and/or sintering thereby risking that the piece can be deformed. There could be a point in using for instance aluminium oxide (or something which doesn't set or sinter at the temps we are dealing with) in a similar manner with the purpose not of saving space but of strengthening complicated pieces during demolding: 1. Cast the slip in a silicone mould consisting of at least two pieces. 2. Freeze until completely solid. 3. Remove from freezer, take away one piece of the mould and put on a mix of aluminium oxide (or equivalent) and water (with the same mix of ethanol or whatever is being used in the slip). 4. Freeze again. 5. Remove from freezer and remove the other half of the silicone mould. and add another layer of alu.ox and water. 6. Freeze. 7. Put in alu.ox. powder, as would be done with less demanding sculptures, and sinter. Doing this would make demoulding easier and would ensure a firm packing in the alu.ox powder. The water in the supporting powder would just dissappear and therefore the alu powder which have been mixed with water should not disrupt the shape due to uneven shrinkage. This idea is just in my head so far so I don't know if it works. Furthermore I hope the bronze ice will work without it in most cases as i adds another step in the process. However a step which shouldn't be so difficult to perform. (And also note that the "casting line" (sorry cant remember the correct English term) between the two pieces of silicone mould needs to be removed before the first layer of alu.ox.water is added which could disrupt a piece that is very sensitive and demanding.)

I think that something in the line of the above idea will be necessary when making hollow pieces since the bronze ice is more brittle than the bronze wax (the trade-off for the decreased toxicity). What I mean is: Cast the bronze ice hollow (more on that below) and then fill the hollow with alu.ox and water and freeze to make it stronger.

Instead of bentonite. Refractory. It doesnt need to dry. It sets. It should behave the same way as bentonite, in the sense that its high temp, and wont fall apart during sintering. It will only harden. I have accelerators for it and can get faster ones I think. I will sinter it later in the week or next week at worst, i think.

This sounds interesting for those of us who want to be able to cast instead of directly sculpting pieces (bentonite bronze clay probably better for the latter?). Have you kept track of about how much of the refractory you used relative to the bronze? What refractory? Interesting to see how it turns out.

Daniel, are you able to place your frozen Ethanol-bronze Iced part into the Alum. Oxide powder fast enough before it is able to start to melt?
What I learnt to do when it was time for the female figure was to take out the mould from the freezer and remove half of it and hold it in the other part so that my body heat didn't heat it too fast while chasing it (some defects in the mould made it necessary). Thereafter reverse it to chase the other side. I did put it in the freezer in between but that might have been necessary only since I hadn't let it freeze for long enough time since I was in a hurry to get started. It could be beneficial to freeze the powder and the can the sculpture is to be packed in before putting in the piece to give you some more time to pack it properly without the powder heating it too fast. Possibly necessary for some pieces.

Mark - Interesting to hear how you have gotten hollow casts, using bronze wax I take it. So the nitrogen cools the mix enough that it sets after slushing? Co2 would be ideal to do the same with I presume.

I did a failed attempt to hollow cast bronze ice for the female figure. For the bronze ice I tried to freeze a mould prior to sluch casting. With the type of mix I used then (the slip which needs to be stirred before pouring so that the bronze and water solution doesn't separate) the result was unfortunately not a hollow cast since when the slip met the cool mould it became less runny and wouldn't really be hollow cast. (One reason why I failed could however be that I had a very small amount of bronze ice mix left, maybe 0,3 kilo, which meant that too much of it was cooled down to fast in a manner which could mean maybe that a bigger sculpture could be sluch cast using the method) I think that different mixes needs to be tested for the bronze ice. Possibly its better to do the way you did it and have a room temperatured mould, slush cast and spray with cooling gas instantly so it freezes in the desired shape. This will really take some experimenting.

About the co2 turning to carbon monoxide, not too sweet.. I have had good ventilation when I have done this so I haven't noticed anything and since there is little oxidation on the pieces I would assume that not that much carbon monoxide has been released? Are there more opinions/information on this issue?

/Daniel S.

[enitharmon]

Hi Daniel,
I read an old patent on using bronze ice, they applied 50 tons pressure to get it to work.
The metal grabs one of the oxygen atoms and leaves CO

[DanielUCM]

Enitharmon - Yeah, I've seen a patent on freeze casting from the 60's. With the pressure you refer to there would probably be no need of suspending it in the alupowder but then it would not be doable for our purposes. The more recent articles that I have mentioned in passing previously does not involve using pressure for the casting. I'll try to get ahold of the references for you. (I have however so far not seen any reference where bronze has been explicitly used, or when a hollow freeze cast is desired.)

/Daniel S.

[jphariot]

Enitharmon,
I think for now, I will use the co2. My Kiln is outside so I have no worries there.
I will consider the other options for later.
Daniel,
I actually tried to dip a iced bronze part into a gypsum-fused silica slurry last night. The surface of the frozen ice just dissolved or started to melt immediately. The water used for the slurry was ice cold too. I think that and what your saying about the part needing something that is flexible is leading me to other ideas.
Yes, the refractory parts work. Basically a calcium aluminate cement. My test was a ring so the amount was so small my scale couldnt detect the powders.
But it was close to 5%-10% refractory. I also added lithium carbonate as an accelerator. It set within the hour. Demolds nicely. I need to go to photoshop and get some photos together. This week! Still not sure how it will sinter.
Assuming it sinters nicely, What I dont like about it, is once youve mixed it your commited. I want to use silver powders, so once that refractory is mixed any gates etc are wasted. I imagine one could melt it and flux it etc. But I want to get away from all that. But for bronze and stainless it might work out nicely. I will sinter this week and let you know.
I also tried sodium silicate today. Man, I forgot how strong that stuff was.
Mixed it with the bronze powder and since my co2 tank still needs gas, I remember sodium silicate sand molds are sometimes cured in microwaves. So I dried it or cured it in a microwave. Real hard. Didnt seem to need much sodium silicate. I baked some sod. silicate in my kiln to about 16ooF and it becomes like glass. So I am making an educated guess that it might behave something like the bentonite? Probably will add brittleness. I will sinter that too. But I recall making sand molds with sodium silicate and co2 and it sets in a co2 environment immediately.
The frozen bronze slurrys I casted into silicone came out really nice. I mean almost all the detail. Too bad I cant take it any further yet.
Daniel I have another question:
Sorry if I asked this already a bunch of times. But I am still not clear as to why you are using ethanol over water? Is it because of the crystal formation patterns on water? OTher than that it should behave the same correct??
Can you use any other type of alcohol?? I have no idea where to get ethanol?
Use scotch or whisky? There arent any gas stations that sell ethanol here in L.A. yet. Isopropyl, which is methanol, i think ? will that work?
I want to try the frozen part into the Alum oxide. Would another powder like fused silica work? I have some of that and I think that I have Alum oxide for sand blasting or for tumbling actually ,but im sure its of a rough grade.
Did you have to pack the alum oxide tightly around the part? Do you put the iced bronze part and alum oxide in a stainless steel container? Am I on the right track or way left field?

Also, Mark, if you see this, I bet we would all really like to hear from Rand German. I think thats who you mean? I talked to Dr. Struve, I think his name is and he said that Dr. Rand German has an excellent book out on the subject.
Do you think that would help?
Thanks again,
John Hariot

[Harryman]

I just heard about the breakdown of CO2 to CO this week also, I'd be cautious, but I can't imagine that the volumes we're dealing with would cause instant death. Not all the CO2 will convert, just some of it.

As for a source of ethanol, see if you can source alcohol fuel for race cars. They use ethanol. Some jewelry supply places probably stock it as well for alcohol burners.

[Burkhard]

Hi all - still trying to get my non-sculpture working life in order so I haven't visited the site lately, but some quick thoughts about the CO2 issue:

- If you want to run your kiln inside use nitrogen or argon gas. However, I would not recommend running your kiln inside unless you have really, really (I mean really) good ventilation.
- You should always have excellent ventilation whenever you fire up your kiln no matter what you do - high temps can lead to decomposition of stuff giving potentially toxic fumes (e.g. acid fumes, carbon monoxide, sulfides etc). Be careful!
- I wondered about the CO2 decomposing at high temps in presence of metals. That's why I ran a number of tests to see if the sintering worked before setting up my system BUT I do not claim that no carbon monoxide is potentially produced so be careful, especially when playing with different metals.
- For bronze powder, my only observation is that the reaction between the metal and CO2 (to give carbon monoxide) should also give a metal oxide. The fact that the bronze sinters leads me to suspect that the amount of bronze oxide (and hence carbon monoxide) is relatively small, else the bronze would not sinter.
- Other metals or higher temperatures may produce more carbon monoxide - don't know, be aware.
- If you have any organic binder in the system (e.g. the wax from the Pilato process, methyl cellulose, glycerol, paper pulp) you will probably get much more carbon monoxide from the breakdown of the wax compared to any carbon monoxide formed from reaction between CO2 and the bronze powder. This is why you have a burner at the outlet pipe of the pot.
- If you're unsure use nitrogen gas.
- Did I mention good ventilation???

Oh and did I mention to be careful???


With the ethanol - isopropanol (rubbing alcohol) is not the same as methyl alcohol (but just may work). Ethanol here in Oz is also sold as "methylated spirits" (this is basically ethanol with 10% methanol to make it toxic and a small amount of foul tasting stuff to make it undrinkable), sometimes it's also known as "denatured alcohol". I'd be very surprised if you couldn't find a similar product in the hardware store. I doubt whether the small amount of methanol would seriously affect the properties.

Now I just have to find time to look at the interesting posts from the last couple of weeks. :)
cheers all

[DanielUCM]

John, it will be nice hearing about your results. Sounds like with the sodium silicate you wouldn't be as committed as with the refractory, and you could use any leftovers several times before curing it? I think that is one of the benefits of the methods we have tried so far, that they can be used over and over until all is used up.

I like hearing that you are on your way with the bronze ice also. The more experiments we do the easier it will be to solve the remaining problems.


Sorry if I asked this already a bunch of times. But I am still not clear as to why you are using ethanol over water? Is it because of the crystal formation patterns on water? OTher than that it should behave the same correct??
Can you use any other type of alcohol?? I have no idea where to get ethanol?
Use scotch or whisky? There arent any gas stations that sell ethanol here in L.A. yet. Isopropyl, which is methanol, i think ? will that work?

Ethanol I add to the water that I mix with the bronze so that there will be no ice crystalls (or smaller crystalls) formed during the freezing. I don't want them because they will cause porosity and decrease the compactness of the bronze/steel. But note that I only add a little ethanol, like 10 volyme procent (around 13 weight procent?) I think that the alcohol has some other benefits as well but I'm not quite sure. I get the ethanol in gas stations, the alcohol that is denaturated (some chemical is added so most people can't drink it). It's the type used for camping kitchens, to remove stains, etc. In Sweden its coloured red. It sells in 1 litre or more. I think that i would stay away from methanol since it is toxic. Glycerol is an alcohol but I haven't gotten it to work, mainly I think that it has some properties which needs to be countered with other substances (or so it seem based on my reading of an article on the subject). The alcohol used should not increase surface tension, and not decrease the freezing point to much when mixed with water.

I want to try the frozen part into the Alum oxide. Would another powder like fused silica work? I have some of that and I think that I have Alum oxide for sand blasting or for tumbling actually ,but im sure its of a rough grade.
Did you have to pack the alum oxide tightly around the part? Do you put the iced bronze part and alum oxide in a stainless steel container? Am I on the right track or way left field?

I think Burkhard used zirconium..something. Something which doesn't sinter at the temperatures of what you want to put in it should do. It must however be really fine powder. Ceramic supplies carry it.

I think that for the packing someone has mentioned using the vibratory table to pack it. I have just manually shaken it a bit and tried to make sure there is powder everywhere around it, tightly, when I pack it. A method where the piece isn't destroyed and which packs the powder tightly is good. That's why I think it could be good to cool down the powder before packing, gives you time to pack the piece properly before it starts to melt.

/Daniel S.

Edited: Ah, Burkhard, good to see you, didn't see you had explained the ethanol thing already when I posted this.

[malakiblunt]

Hi Guys im new hear and am realy impressed with the development work your doing here.
The only thing i have to add is if cabon monoxide is a worry why not get a home carbon monoxide alarm ? you can then test to see if it is produceing dangerous levels,and take sutable precautions or no that its not a concern.

keep up the good work

philip

[jphariot]

Harryman,
Yes, in fact I was thinking of converting my car to ethanol and making it, but I read it takes a lot of corn to make a gallon and time-energy. I dont know of any formula racing locally though. Yes a jewelry supply would seem easier. But in fact, Burkhard is saying hardware store and I think that will work fine. Thank you.

Burkhard,
Thanks for the Carbon Monoxide-Co2 info. I think your rule of good ventilation should even apply if we were doing plain ceramics right? Who knows whats going on at 1800F?? So outside is good enough air circulation for now. Ultimately I will bring it inside, but will build some big ventilation fans.
Also, I was going to ask about "denatured alcohol" and sure enough you beat me to it. Thats what they call it here in the States. Perfect. I can get that right around the block here at a hardware supply.
Also, Any thoughts on using Fused Silica as a powder to contain the frozen part during sintering??? Instead of Alum. Oxide?
Thanks!!!!

Daniel,
Yes, what I like about the Sodium Silicate is that it is water based. And it will dissolve again in water after its dried. Not sure how it might affect bronze if it sits for days as a clay or slip? Not sure how it will sinter? But its strong so it doesnt seem to need much to bind the powder. Way stronger than bentonite as a binder , in its green state. Its also inexpensive. I think Non toxic.
Yes, I have a small frozen bronze figurine in a silicone mold in the freezer right now. Half of it actually, its only for a first test. I plan on setting that into a powder and sintering.
As far as powders, I dont see why Fused Silica would not work. Its shouldnt melt at 1650F. Its made for high temp applications. I cant remember the melting temp. I could go look it up in my notebooks but its way up there, I am almost sure. Its also a fine powder. Like flour.
I hope to be able to fill up my tank of co2 today and get testing tonight. I have parts sitting there waiting. I will send photos, if there is something positive.
Good luck all!!
John Hariot

[jphariot]

Have another question: My kiln does NOT have a digital display-control. Its analog. How critical is the temp. I am not sure how effective a reading I will get with that pyrometer. What if I go 50 degrees F above?? How critical, or how much room for error do I have???
Thanks!

[jphariot]

Hello gentlemen,
I am going to sinter tonight. I have my tank filled. Burkhard stated 200ml per minute. My regulators only read psi(pounds per sq. Inch) and bar. Does anyone know how that would translate? Anyone else use this kind of regulator? I am just going to set it at a low setting. I am dying to try these small parts.
Also, Welcome to Philip. Yes a carbon monoxide reader would be helpful if we are doing a lot of this indoors. will keep that in mind.
Thanks,
JOhn Hariot

[DanielUCM]

Philip - Good idea, do you know where such carbon monoxide alarms are most commonly found? Hardware stores or automobile related stores?

John - Keeping fingers crossed that you will get good results. As for the sintering temperature for perfect result it seems according to others on this thread that having exact temp is pretty important but to just test if a method, and your set-up, work or not I'd say better a bit too hot than too cold (rather 900 than 700)! But that's just my personal idea.

/Daniel S.

[jphariot]

Daniel,
Got a few that worked. One was the bentonite. Worked fine. Real smooth. In fact I poured the bentonite formula like a slip. And then microwavdd it to make it harden. It was only poured into a one part mold. Not 2. So it was easier to dry. Good detail, surface way cleaner than my investment castings.
I am putting a few hours into today while i wait for other stuff to set and cure, dry etc. I think the freeze method is next. Bentonite is fine, but still how can I dry it in a 2 part silicone mold. If there was some way to make it set in there. THen dry it outside the mold. I m working on it. Will post pictures soon.
Also, no problem with sintering temp. My pyrometer seemed to be good enough.
sintered at 1650F

Thanks.
John

[enitharmon]

Daniel,
I chatted to my metalurgist friend, he said fire too fast and it will crack, and black spots show oxidation, the black parts on your previous photos are from using the CO2 or leaks, where the metal has found the oxygen. But hey maybe they will sand off.

[jphariot]

Enitharmon,
I suspect you are right about Daniels black spots. I tried the freeze method in the powder and it worked, but not that nice. It shrank terribly, and was pretty black. It did seem to atleast partially sinter. I probably needed more gas.
I suspect its the powder. The gas may have a hard time permeating the powder.
After all the lid has a weight on top but not a seal.
But the co2 worked fine with the bentonite method. I was delighted.
And one benotonite totally distorted because I ramped the the kiln up fast. But it still sintered nicely. Also bends too. So I am delighted.
I will do some more experiments with the freeze. I still think Danile is onto something good.
I may try nitrogen the next time around. Costs the same and my supplier has it. But want to empty out my co2 for now.
I keep promising photos, but ive been super busy with investment castings.
I have another piece in the kiln right now.
Will keep you all posted.
Thanks,
John

[DanielUCM]

John - Great hearing that you have gotten some good results! Yes, the bentonite formula is the most mature of the two new methods but I will also continue making some more freeze casting tests. The advantage of having an end result without any additions to the bronze is a big one. And also getting a stronger piece when demoulding.

Will microwaving the bentonite-mix before demoulding make it easier to demould compared to regular drying, or is the advantage mainly that it goes quicker?

Strange that the bronze ice shrunk so much, my experience concerning shrinkage have been quite good. The main problem that is left is to improve the surface. Not just the dark spots, cause they will probably go away when I have a tighter set-up, what is the biggest challenge is the sort of bumby surface that is still there. Like I have said I believe I have to make a more homogenous mix. I just have to get ahold of some more bronze powder!

Looking forward to see some pictures!

/Daniel

[jphariot]

Daniel
I think the microwave helped considerably. I need to try it again with the bentonite. I am still not documenting much. Although putting a lot of time into it. Just trying to get a feel for it.
I did notice my bentonite piece can be broken with pliers. I have to bend it back a little but it can be torn off. Probably way too much bentonite.
How do they compare for you??? Is the Iced Bronze result stronger than the bentonite formula?? Can you bend them back the same?? Again, I made a tiny batch so my scale couldnt measure it. I probably have way to much bentonite.
Also, sometimes high protruding areas of my parts are not completely sintering.
Atleast on the surface there is a skin of non sintered powder. Its not black but brown. I think maybe oxygen was touching those areas??? I am going to try nitrogen, I think, if my regulators will work with nitrogen??
Also I am looking at a photo I took in photo shop. What file format do I save it in to be able to load it onto this site?? I would like to add some images.
Keep up the good work.
John H.

[DanielUCM]

John - Since my bentonite bronze clay failed due to either not being properly mixed or since the bentonite was too coarse or of bad quality I can't compare the two yet. My bentonite pieces didn't sinter properly inside and had at least one surface all bubbly (see previous results). Since I have run out of powder (trying to order new but having trouble getting ahold of my supplier during vacation times..) I haven't had the chance to make a proper mix and compare the methods yet.

Concerning file format, I think i usually choose, "save for web", and then JPEG (or JPG or something) and "high" quality rather than maximum so the file doesn't get too big.

Best wishes

/Daniel S.

[jphariot]

Daniel,
Yes, the bubbly sintering. That happened to me. I think its due to drying too quick, but I am sure you figured that out.
I have tried both 100 and 325 mesh both work well. Sometimes I get a lot of shrinkage sometimes little. I have not figured it out yet.
Now, my main problem is the strenght. I am able to tear the Bronze too easy with pliers. Kind of weak. I probably have too much bentonite. So now I am trying another test with about 5% bentonite. These are small samples and are hard for my scale to read. As soon as I have more confidence I will go for larger
Pieces. Next time I will also try nitrogen. After my bottle empties. Sometimes,
part of the sample piece doesnt seem to sinter fully. Like an eight of a millimeter of something is powder. It seems like its the opposite side of where the co2 is coming in from.
As far as saving my file, my photoshop version is old and doesnt have save for web. But maybe I can just save the file in a reduced size and it might work right??
Thanks
John H.

[Harryman]

John,

In Photoshop, go to "image size", set the dimensions you'd like for the photo, set the resolution to 72 dpi and then save as a .jpeg as Daniel said. A decrease in quality will decrease the file size, but these days it's not that big of an issue. "High" should be plenty.

[DanielUCM]

Bronze powder prices?

Just wanted to check how much you guys have paid for bronze powder lately? What quantities have you bought and what alloys and particle sizes? I have just gotten in touch with the company I have bought powder from the last time (almost a year ago) and apparently the increase in copper prices has almost doubled the price of the powder over the last year and a half. Earlier it cost around 28 dollars per kilo, now around 54 dollars per kilo. And that is quoted when I asked for the price when buying 25 kilos.

At present I could actually get a better price buying from an art supply (!!, possibly they haven't updated their prices in a while..) rather than from this industry place. Except that from the art supply I have had to ask what alloy etc. exactly they are selling (its the stuff used for cold casting). I have begun looking for other suppliers and other alloys and particle sizes to find something more affordable.

Would be great if we can share some info on this in order to have something to compare with.

/Daniel S.

[jphariot]

Harryman,
Thanks for the photoshop help. So its a matter of file size and not file format.
Thats easy. I am not a huge photoshop user, but I use to use to touch up photos etc. , so that is easily understandable.

Daniel,
Don't pay a lot for the powder!!! Unless you do not want to import and there is no one else in Sweden. I payed about the same price as Bronze ingot. I searched and searched. I was concerned that it would be way way more than ingot, but found out it isnt. Its very close. In fact, the samples I purchased were LESS than what I payed for ingots. I payed about $5.oo a LB. for the sample. 100 mesh. Normal prices at that company were $7.50 a LB. or around that. For whatever reason they sell samples cheaper. I was paying around $10.00 a LB for ingot. I had to buy a lot to get 7.50 LB.
Also, I found 2 atomizers. And if I send them Scrap Sterling, they will send me the powder for only around like $2.35 an oz I believe. The other wants around 3.25 and oz.
Do you want my source for bronze??? They could ship it I imagine.

Ok, I am planning on testing the bronze with nitrogen. I cant get consistant sintering. Even the best ones, which turned out pretty nice, still have some areas that have powdered bronze. Its usually the high areas, like the tip of a nose. It can go about up to a millimeter in thickness, then under that is hard sintered metal. Do you guys get this? Why would that happen???
Maybe the problem is is that I have been drying the bronze powder in a small oven at about 200 degrees F. With no gas. So i wonder if it is oxidizing ever so slightly??? It does not look oxidized.
I was also thinking that maybe i am not hitting it with enough temperature during sintering??? I dont trust these analog pyrometer/thermocouples. How accurate are they?? Not sure. But if It wasnt hot enough, I dont know why it would not sinter only at the surface and especially on high areas???
Any thoughts??
I will go to photo shop right now and try to save and bring back a photo before i get back to work.
Thanks Lads,
John H.

[jphariot]

Harryman,
I reduced the sizes of the images, But when I go here and click the insert image
Icon it is asking for some text to be formatted?? what does it want??
How do I add my images??
Thanks,
John H.

[Harryman]

I'm not sure what's going on with your images.

Make sure you save it as a .jpeg after reducing the resolution to 72 dpi and reducing the image size to 10 x 8 in or something resonably small.

Go to Manage attachments (here in the forum when you reply to thread), browse for your image on your hard drive and upload it.

You can preview post to make sure it looks OK.

[DanielUCM]

Even the best ones, which turned out pretty nice, still have some areas that have powdered bronze. Its usually the high areas, like the tip of a nose. It can go about up to a millimeter in thickness, then under that is hard sintered metal.

I haven't had that problem since I started the tests using a co2 atmosphere. As you know I still have problems since I haven't gotten a tight enough set-up yet, but getting a powdered surface is definitely not a problem. I sinter at a few degrees over 880 Celcius. Perhaps you should raise the temperature fifty degrees Celcius or something above what your pyrometer claims to be the temperature? I mean it shouldn't melt so at least than you could confirm or rule out problems with temperature. You should probably turn on the gas as soon as possible 'cause remember at the small rates of gas per minute that we are working with its going to take a while to fill up the entire kiln and all the powder. If the piece is allowed to warm up to much before turning on the gas and if it has to wait before all oxygen is gone maybe the surface gets oxidized but not the core?

Thanks for the information on bronze powder pricing!! Good to hear that you don't have too pay too much. Would be great if you let me know from where you bought it, but maybe too expensive to import from the US. (I have to search for what 100 mesh is in micrometer.)

/Daniel S.

[jphariot]

Harryman,
I will do just that regarding images. Thanks.

Daniel,
Yes, you know I was preheating the part in an oven at about 200F or a bit over and I may have been slightly oxidizing it??? It sintered pretty good yesterday. I dont think I had any surface that was dusty.
Try "acupowder" www. acupowder.com you can order over the website.
or call ken watson at (908) 851-4500 If you want 100 mesh fine Bronze order the "5890" Bronze powder. Works fine. $10.00 for 1 LB. Bag or $25.00 for 5 LB bag. i
They also have other alloys. If you want silver let me know, I have 2 more sources.
Now, I was hearing that we can use activated carbon granules for sintering. That it works nicely and you can use it over and over again?? I was thinking it might be more economical and easy to pack many parts without needing all this kiln shelving. Just layer over layer of granules in a box. What do you guys think?? I think I can get activated carbon at a fish store right??
Thanks again,
John Hariot

[jphariot]

Gentlemen,
Here are the first 2 images.
Thanks,
John H.

[DanielUCM]

Congratulations! Great to hear that the powdered surface problem is over. Did you use the bentonite method for the pieces in the pictures? The pictures are however too small. Could you save them in a larger format or something so they open up in a new window when clicked?

Yes, the carbon method, might be worth looking into. Is the idea that you have the piece to be sintered in a close container with the activated carbon, and the carbon attracting the oxygen so the environment becomes oxygen free? I will do some searches for this.

/Daniel S.

[jphariot]

Daniel,
Yes, bentonite. But it is hard to get out of molds effectively. I am going to do some testing with baking etc. I will let you know how it goes.
As far as prototyping goes, or one offs, Rio Grande is going to be selling a bronze clay in a few months. I need to do production, but it seems like you lads want to do one of a kind art peices or maybe several copies.
I talked to the man who developed this product and it sounds like it might be perfect. It might be priced pretty good. Maybe double ingot costs. That is not bad. He also says that it can be cast like a slurry. No brittleness because the binder burns away. And it doesnt need gas because it works with activated charcoal. So Go to riogrande.com in the next few months it should be there.
Maybe you can use that?
I will be testing a trial sample and can let you know how it goes. I want to use it for prototypes. Mayb produciton but I need to test it for that.
Also, are you still planning to freeze dry?
I have another binder I need to test. Its a thermoform resin in powder form.
I should get to that in a week or so. I will let you know how that goes.
Did I give you the number of the bronze powder source?
Thanks again,
John H.

[DanielUCM]

John - I have actually finally found another source of bronze powder here in Sweden where I could get it for around 21 dollars per kilo (I guess that's around 10dollar per pound). So with the bigger shipping costs from the US (and potential customs fees) I think it is a good price. And I will likely get a smaller particle size also. I will talk to the supplyer tomorrow to finalise it.

How has it gone with some of your other binder experiments? Since I can't do any experiments myself until I get the powder I wanna know what you and the other guys are doing.

Sounds good that the Rio grande binder burns out.

Burkhard - Have you got any ideas about the activated charcoal method?

/Daniel S.

[enitharmon]

Daniel, activated charcoal has been used for some time in saggar chambers,[pottery web sites in 1998 were talking about it, in fact they also discussed the same design as Mark's stainless steel chamber]. This is for reduction [of oxygen] firing in ceramics to bring out the metalic quality of the glazes. A problem for electric kilns is stripping the oxidation on the electric elements in the kiln and they avoid this by using the saggar chamber in the electric kiln.

The oxygen is burnt off inside this chamber by the charcoal...raku firing uses a similar principle..fired pots with metalic glazes are quenched in saw dust inside bins with the lids closed...outside of course. Graphite can also be used.... in fact that takes us back to the beginning of the thread...microwave technology .... a patent I read uses a mix with particles of graphite in the feed stock to allow sintering of the metals in the microwave 'oven'.

yours Enitharmon

[DanielUCM]

Enitharmon - Thanks for the additional information! When we discussed this subject earlier in the thread we aired the concern that it would be a pretty messy affair to use activated charcoal to get the reducing atmosphere, what do you, and you other guys, think about that at this point? Will there be a lot of sooth finding its way out of the kiln or is activated charcoal not behaving the same way as normal coal?

/Daniel S.

[jphariot]

Daniel,
Yes, $10.00 a pound is good. I would go for it too.
I just opened up my new binder that I got in. Upsetting. I asked for a powder, and it came in granules. Tried to grind it down but its not going to work.
Still running tests with the Methyl Cellulose. Its not as bendable as my bronze castings. It will crack at about 90 degrees. Maybe I am not sintering enough??
I wish that the Bronze Clay was already for sale at Rio Grande. I am awaiting my test sample. The owner of the company put me on the wait list.
It sounds like a good product. He said that it is not brittle.
At double the price of ingots I think its a good deal. I would still mess around with other formulas just to have more tools, but it sounds like a good all around product.
I tried the activated charcoal and it works fine. That is what the Rio Grande kit will come with. Its a good idea. I was doubtful, but the owner of the product said it worked great, so I started to think that it was a good idea. And now after trying it I am really impressed.
Any ideas as to a powdered binder that is a thermoform? I am going to look for some polyvinyl acetate. I think they use that for metal injecton molding??
Kind Regards,
John H.

[DanielUCM]

Sorry to hear about the wrong binder size. I got some test samples of a couple of different bronze powders from my new supplier. One contained a bit of phosphor (P) and turned out to mix really well with the water and ethanol mix (for bronze ice) when compared to the regular tin-copper alloy. I will do a test run within a few days to see if there are any differences in the end result.

So, John, you have tried the activated charcoal, could you say something more about that? Must you be outside or is it clean enough to use inside? Does it smell?

/Daniel S.