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