Suitable Mold Materials for Clay Puppets

I'm trying to figure out how I could melt down some van aken clay and pour it into a mold. I don't have a vacuum chamber, so I worry about silicone. 

What's the best material to make the mold out of? Can I use Ultra-cal? I do like the idea of a more rigid mold, however, I do worry about it being harder to release the finished clay figure.

I'd prefer something longer-lasting (alginate had me excited before I learned how short-lived it can be)

Looking forward to hearing from anyone with experience in this. I'm eager to start making some molds! :D

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Yot don't need a v chamber just mix slowly and pour into you mold box containing your sculpture in a thin stream to help pop the bubbles that remain

You don't need a v chamber just mix slowly and pour into you mold box containing your sculpture in a thin stream to help pop the bubbles that remain

If the idea is to cast several duplicates of your clay sculpt in plasticine, then you do want a flexible mould.  You make a hard plaster mould so you can cast your clay sculpt in silicone or latex, both flexible materials.  The original clay comes out, but not undamaged, it needs squeezing out of shape and often you have to dig it out in bits.  But that's ok because you have made the mould.  But not ok for your melted plasticine casts.  Better if you can flex the mould so they come out without distortion.  

I use a silicone called Pinky-Sil, fairly quick setting, for moulds of my plasticine sculptures. (Possibly an Australian brand, but there are others.)  I used to work for a plaster company that always de-aired the silicone for their moulds, but I have been making silicone moulds for about 30 years since then, without access to a vacuum pump and chamber, and it isn't usually a problem. They used to use an electric mixer on the silicone, so it probably did need the vacuum chamber to get the bubbles out.  But I mix by hand and don't whip it into a froth, just a slower stir, and it seems fine without de-airing.  

Alginate is good for one-offs.  Sometimes if you are lucky you can get 2 cast out of it, but it soon begins to shrink as the water evaporates, and after the second or third cast  it will usually tear.

Natural liquid latex can be used as a mould, but I don't like it for that, because it shrinks a bit and can easily go "drummy" - where there is a hollow in the sculpt, it can shrink away a bit and flattens out, so it is stretched over the hollow like a drum skin instead of going right down into it.  Then the cast is flatter, not the original shape.

There are some urethane rubbers that might work but I can't say I have used them.  I go with silicone for flexible moulds. If there is a likelyhood that the silicone could distort under the weight of the melted silicone in it, I usually make a case mould - also called a mother mould.  It is a hard shell of plaster or fibreglass that goes around the outside of the silicone to keep it in shape.  When the cast is set, you remove the mother mould, then flex the silicone and peel out the plasticine cast.

Thanks for the advice! I'll definitely get some silicone and try it out. Seemed a little pricey compared to the other options but I'm sure it's worth it

StopmoNick is right on about latex shrinkage, but I think I'd try it; depending on what you're molding, it may not be a big deal.  Also, you may try this: I recently had to sculpt a medusa head (see the pic) and I didn't want to sculpt every snake head individually.  The bust was sculpted in Roma Plastalina, but the snake heads were Van Aken. What I did was:

1. Sculpted one snake head in Plasticine (I don't remember if it was Roma or Van Aken, but it doesn't matter).

2. Made an alginate mold of the snake head.

3. Put the mold with the snake head in it into the refrigerator for a couple hours to stiffen the clay.

4. Carefully removed the clay and then poured in melted paraffin wax and stuck that in the fridge for a short time.

5. Repeated the process about a dozen times; the original alginate negative held up for all of that.

6. Put all my snake heads on a paraffin wax bed and did a new alginate mold of all of them at once.

7. When the alginate was set, I pulled out the wax heads, melted Van Aken in my crock pot, filled the alginate and stuck the whole thing in the fridge to stiffen the clay.

8. Pulled out a dozen identical snake heads.

Don't know if you can use or modify the above, but I hope it helps.

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