best mold material?

[vnoelleb]

I am just finishing a lifesize horse sculpture, and am looking to cast multiples in plaster (a herd). Any suggestions would be much apperciated as to what sort of material would be best for the mold. While in school I used latex, maybe or polyeurathane which worked well, but that was more than a few years ago, and of course I've lost my notes. Also any links or lit would be fantastic!
Thanks!

[ironman]

Hi, You can use plaster for the mold too!
Have a nice day,
Jeff

[fritchie]

Vno - Plaster can be used for the mold, of course, but if you want many castings, it probably would become chipped with use and generate more work on each ensuing cast. I would recommend a polyurethane contact or primary mold with plaster mothermold.

You should find much discussion here on molds, with the search function, but moldmaking really requires more detail than can easily be communicated in words. Why don’t you do a search and then ask about what seems promising?

[dm2004]

I am just finishing a lifesize horse sculpture, and am looking to cast multiples in plaster (a herd). Any suggestions would be much apperciated as to what sort of material would be best for the mold. While in school I used latex, maybe or polyeurathane which worked well, but that was more than a few years ago, and of course I've lost my notes. Also any links or lit would be fantastic!
Thanks!

There's a 50/50 mix gel stuff?? can't remember what it is. here's the web site www.smooth-on.com/default.htm. You can get about 50 cast out of those rubber molds before they start to pull apart, if you cut them to pop open right. Plaster molds chip or break after 5 uses if your lucky. Plaster best used as a waste mold "cheap". But i'm going off my hands on know-how. I've only tried rubber and plaster molds, well other then sand molds.

mib

[magic touch]

Well, I don`t know what your budget is for this, but if it was me I`d go for a silicone rubber mold and fiberglass jacket. That would provide the strongest mold that would stand up to multiple castings.
Making a plaster mold would require a very good knowledge of multi-piece mold making- I wouldn`t reccomend it, unless you`re a very confident mold maker.
Polyurethane ,while cheaper than silicone, has it`s drawbacks.One being it`s weaker than silicone.Needs a release agent to avoid your castings sticking to it, and it`s also not so good for your health.
Latex is not something I`d really reccomend for such a large scale mold.It work for small castings, but you really need something more accurate for a mold of this size.Also a latex mold would take forever to bulid up a sufficient thickness on this scale.
Hope this helps and hasn`t come to late.

Jamie

[Toby]

I'm still experimenting with clear builders silicone with glycerine and acrylic paint added. I'm getting good results from spray-on foam too but it's not too cheap.

[underachiever]

Silicone rubber mold is the way to go really, if you want to go multi, but it's sorta expensive though.

Oh, and how do you do a fiberglass jacket? Unless it's a plaster jacket with fiberglass in it....

[Mordachai]

It's really a cost issue -vs- a use issue if you think about it. How much you want ( or can ) spend on the mold and how many times you need to cast in it should determine the materails.
I personally think that making a mulitpiece mold, of either plaster or fiberglass or poly-plastic or forton, the same skills are required.
I actually think that the plaster molds are easier, because they are easy to slean up and easy to add on to.

I don't recommend plaster simply because of the weight and the mess. Is IS going to be pretty hard to move a fullsize horse sculpture mold made of plaster. I've made much smaller molds out of plaster that the Bronze fundry complained about because of the weight. and they were just casting wax in it. if you are casting plaster, it's going to weigh as much or more than a real horse! lol

As for the mess, I guess it just depends on how messy you are and how much you are willing to scrape the floors( a dirt floor shop is great for casting because of this- you can also spread a thin layer of fine sand on the floor before you start casting. This will make it much easier to scrape and clean up)

If you've ever worked with Fiberglass, you could make most of the mold out of fiberglass itself(I'm assuming you are making a somewhat smooth and realistic horse), and making the detailed parts out of a rubber of somesort with a fiberglass mothermold.

The fiberglass is much easier to cast with and handle and store, also alot stronger and easier to repair than plaster. But it does come with some pretty heavy health risks.

I guess it really depends on what I said at the top.
Just my $0.o2

|M|
( One pic is of a rubber mold with fiberglass mother and the other has 2 molds in the background that are latex and plaster mothers)

[iron ant]

Hey Lost in NY gave you the way to go .Polytek has a variety of flexible mold material,and yes they will require a mother mold.Plaster for a life size horse?If you used hydrocal with fiberglass you could cut down the volume and wieght,but fiberglass would be the lightest.Nasty stuff though,use proper venalation.Afx Studios in Marietta ga could possibly vacuum form your mother molds in plastic?Andre,who is a special effects/sculptor is a master mold maker.Drop him an email.......hey lets see a picture of that horse......

[Mordachai]

yeah, got a picture of the horse?

|M|

[Jamo]

If you don't mind spending a bit more for less toxicity you can go with some two part mix plastics they would make a better mateial than polyester fiberglassing resin. Ick that stuff stinks even after it has set count on a huge headache while working with that.

[Mordachai]

If you don't mind spending a bit more for less toxicity you can go with some two part mix plastics they would make a better mateial than polyester fiberglassing resin. Ick that stuff stinks even after it has set count on a huge headache while working with that.
I've worked with two brands of that epoxy plastic. At first it was strange and unruly, but i got the hang of it real quick.
It's like spreading frosting on a cake!

But it is also pretty nasty stuff, maybe not quite as bad as Fiberglass, but that's kind of like saying cocaine is not as bad a crack!!! IMHO

You are supposed to wear a respirator for that stuff too, it gave me a bad headache the one time I didn't wear a mask.
But it does clear out (fumes) way faster than FGR, making the room ok to walk in quicker!

|M|

[Merlion]

This thread started sometime ago, but the topic of making flexible mold for a large life-size sculpture should be of interest to many.

I am also interested, but have not done it. On the other hand, I am reading a good chapter from a book giving good explanation with many photos of how this is done.

The book is Tony Birks, 'The Alchemy of Sculpture, The Art of Bronze Casting', Marston House, 2004, ISBN 1 899296 20 4. This is the paperback edition. Another publisher publishes the hardback edition which costs more.

The relevant chapter is Ch. 3, 'Making the Mould'.

Although the book is about bronze casting, it gives details of the practice at the large reputable Pangolin foundry at UK. And the chapter talks about how their specialist mould making department makes flexible moulds for large figure sculptures. For large sculptures, the flexible moulds are supported by multiple fibre glass backings. Different alternatives are explained, with photos of different stages of the practice.

[Tirebiter]

Erm, as an aside, in reply to Mordachai's last post, I would exercise caution when solely using your nose to decide whether the fumes have cleared from a room or not, especially if one has had significant exposure that day. Some chemical vapors cause "olfactory fatigue"; that is, they temporarily neutralize the sensory aparatus in your schnozz, and you can't smell them anymore.

Notable examples are hydrogen sulfide gas (a hazard in the petroleum industry) and some organic solvents.

If the MSDS sheets that come with your chemicals are well written, they warn about this stuff.

Use your engineering controls (a fume hood, an open window, working outdoors) to help minimize your exposure.

Heh, not to make anybody paranoid or anything :)


Speaking of somewhat hazardous mold making processes, a friend of mine recently used this cheap-ass quick-and-dirty method to make a mold to produce a wax copy of a slightly larger-than-life commemorative portrait bust for casting at a foundry.

For the flexible rubber part, she used GE caulking silicone (in the silver, not the gold tube) from the hardware store. This stuff tears far more easily than a proper silicone used for mold making, and will yield only a few copies.

For the "print coat" (the layer that captures the detail), she thinned down the silicone with the very nasty solvent, xylene (DO NOT DO THIS INDOORS AND USE A RESPIRATOR IF YOU HAVE ONE; THIS GOOP IS REALLY TOXIC!) and brushed it on.

Next, she gooped on the unadulterated silicone, smoothing it with her fingers wearing rubber gloves (NB, a lot of organic compounds will go right through latex; Nitrile --usually blue or turquoise in color-- is better), using a soap solution to prevent the caulking from sticking to the fingers. Note that good ventilation is necessary for this step also. Recently, we have found that if you swish this caulking goop around under water for a few moments with a pallette knife, it removes some kind of inhibitor, and the silicone cures in minutes instead of hours. She added layers till the undercuts were gone and the silicone was about a quarter inch thick (with knobs on the outside for registration keys).

Then she made a two-part plaster mother mold (held together with nylon stockings while casting). When it came time to remove the inner rubber mold from the original, she just cut a zigzag seam (for registration of the seam edges) up the back of the piece with scissors. With assistance from two fellows, she was able to knock out the mold-making over the course of a long day. Since the bust was a one-shot deal for a local college, she did not need a lot of copies, so it was fine for her purpose.

Oh yeah: and some mold-making professional mentioned to us a while back that you can make your plaster mother molds lighter and thinner by incorporating strips of burlap fabric for strength.

Eric

[realsculpt]

for a life size figure and if you want to get more than one copy you will need to go with silicone, with a fiberglass jacket, you could do a plaster jacket but it will wiegh a ton. I have done alot of large molds for universal studios and disney

getsilicone, its inexpensive but very good. try fxwarehouseinc.com for the silicone, get the fiberglass from a boat supply, but dont be cheap on the mold and dont skimp on the silicone or it will not work, add some cheese cloth to the silicones outer layers. The other option is a latex mold but you will still need the fiberglass shell, and that can burn or overvulcanize the latex.

goodluck
realsculpt
www.realsculpt.com
www,forensicsculpting.com