I'm learning to make plaster molds. The basic principle is fairly simple, when you get right down to the chemistry and physics of it. Of course, the basic principle of aerodynamic flight is simple too, but you don't see me zooming around with my arms out.
I have some Izzy head & torso sets all made up and ready to paint...I'd sculpted their faces and were happy with them, but they won't do for making a mold because they are cloth heads sewn onto bodies in a unit.
What I need are just the heads. So I made molds of the faces with Amazing Mold Putty. Then I made paper clay "masks" using those molds. Then I made heads with balled-up foil as an armature, and applied the paper clay masks of the previously sculpted faces. This took a ridiculously long time.
I'd thought this would save time, but it might have been faster to start from scratch over the foil, and re-sculpt the faces. The proportion gave me fits, but it finally came out all right. I ended up with four heads, three of which I was willing to use to record for posterity in pressed cloth dolls.
A friend of mine said, "Do NOT stick those good heads in plaster until you try a practice one!" Or something to that effect. She was right--I had not planned to do so, but that was the smart thing. Sooooo I used the fourth head...sealed with Modge Podge and then sprayed with cooking oil as a mold release. The head released well and without damage, and I was satisfied I could proceed with the "real" ones.
Life intervened with chores and more chores, paperwork and more paperwork. When I did get back to the plaster, I was so impatient to get started! SO impatient, in fact, that I...forgot the mold release spray. By the time I realized what I had done, I was barely able to save them. One came out with a minor scratch here and there, the other two are "in the shop" for repairs. (The shop, in this case, is the oven where they are drying with their paper clay patches.)
Lesson learned? Slow down. Breathe. Pay attention. Count off a checklist...whatever it takes, but don't get a-head of your self, or you will lose. your. heads.
I would apologize for that horrible, double, almost-pun, but I really have to laugh at this point to keep from crying. More on the Mold Making Progress later. Right now I have to take my head(s) out of the oven.