Moldmaking Water based varnish and silicon mold

If you use decent mold release on your finished work, I don't think it will stick to silicon. Come to think of it, a Brazilian garage kit sculptor, Roberto von Behr uses rattle can clear coat on his female figures to make it extra smooth. And I have never heard of any complain about the clear coat messing up the silicon. But I am confused that why you need to use vernish. Are you usign it to hold the piece together? if so, I would replace the broken parts with epoxy putty/clay.
Hope that helps.

 

Silicone doesn't like sulfur or latex, and the only reason I can imagine using varnish is to try to cover these up. Unfortunately, if you're using a higher quality silicone, the odds are against you if you're trying to cover up possible sulfur. Your earth/mineral clay may have sulfur in it, so you might want to test your silicone on some of this clay first. Fortunately, the only thing silicone sticks to is itself, so when you're using a silicone-specific release, all you're doing is preventing the silicone from bonding to itself.

You don't give any reasons why your polymer clay cracked, but that's something I'd be interested to know more about.

I agree with Switchum, use a latex- and sulfur-free epoxy putty for repairs. I know it's probably too late, but depending on how the face broke, you'll want to reinforce the back/inside (for example, if the face was too thin and broke that way). If the nose or ears broke off, I recommend carving a little groove, so that the putty has somewhere/something to adhere to. Polyclay adheres to itself, even after you've cured it, so if the face broke because it was too thin, you could have just reinforced the face-plate with more polyclay.

I hope these tips help! Good luck!

 

Yeah, that sounds like the issue. Acrylic paint has a moisture content, and moisture can cause all kinds of issues with polyclay: If the water is inside, it expands while the piece is baking, much like when you fire mineral/earth clay. If you soak polyclay in water, it will swell and crack. Water and most things wet are super problematic to combine with polyclay. Next time you need to pigment your polyclay, I recommend using an alcohol marker (which will get all over your hands) or crushed pastel, to which you can add plasticizer (such as any vegetable or mineral oil, or Sculpey softener) if your polyclay gets too firm.

I hope that helps for future reference!