Hullo! Let me try and clear it up for you a little. On the show we take a stone positive of our actor's face (this is literally our actors face made in stone) and we sculpt on it. Then we mold the sculpt and clean out the clay from both sides of the mold. Once we finish cleaning we then run foam/silicone/gelatin in the molds. The space where the clay was becomes the prosthetic. Does that help? If you have more in depth questions, go check out The Effects Lab forums, a lot of people in the SFX industry use it, and are totally willing to answer questions. http://www.theeffectslab.com/forums/index.php :) Hope that helps.
