Experience casting in clay from a flexible mold?

[plyn]

I need help with deciding how to cast a small reclining nude. I've modeled with plasticine, and there are some serious undercuts, probably about 3 or 4. In this case I would opt for a flexible mold, but I really have my heart set on casting in terra cotta clay that I bought. I was planning to press the clay in the mold - I could make a mother mold for support, but I'm worried that since the mold would be flexible the clay might warp when I press it in and/or wouldn't dry out enough to remove the piece.
To cast in plaster looks like it would be a billion pieces and I don't know if I could carry it off.

Anybody have experience casting in clay from a flexible mold?

[ToySculptor]

What you would need to do it to create your mold in layers. First a thin layer of mold rubber, something like GI 1000 silicone rubber, then a harder jacket to hold it all together I recommend Ultracal 30. The layers allow you to demold your piece with out damage because the rubber is thin.
Basically it is called a matrix mold. In your case you need to keep your mold rubber nice and thin to accomodate a peel off demolding of the clay pressout., the stone jacket will have to come off easily and any undercuts there can be handled by breaking down the stone jacket into multiple parts, but still leaving the silicone skin in two pieces. Go to smooth on .com, or polytek.com for examples of what i am talking about, seeing it makes it all so easy to figure out.

I hope this helps.

[plyn]

Thanks for being so specific on the materials. So you don't think casting in terra cotta will be a problem?

[ToySculptor]

As you already know silicone is non pourous so you wont get any toughening of the terra cotta because of the nature of the rubber, but if you do a press in of the clay as you mentioned, make sure the clay is a handleable {if that is a word} consistency, once you have pressed it in to each side, score lines across the exposed clay surfaces, apply a spritz of water to each side and join the mold halves, maybe strap the mold with old straps, I would let this sit an hour or so and then carefully remove the stone jacket from one side, then remove the silicone, starting at the edges and peeling back around the undercut areas.
Maybe allow the exposed side to air dry a little, then remove the otherside.

[plyn]

I know what you mean, make sure the clay is of similar consistency, and probably as dry as is able to be handled.
If I'm successful I'll let you know.
Thanks
plyn