Plaster can be used for casts actually. I've helped make latex masks and we used Plaster for molds. Now after 4-5 casts with latex they were usually scrapped, but it could be done. But yea it was REALLY hard to de-mold (You have to grease up the clay model pretty good before casting) and it is really expensive. Sometimes.....at least $150 a mask assuming you have tools and a armature already. Not to mention that using plaster is VERY DANGEROUS if not used correctly. My friend doesn't have any hair on his right arm because he chose not to read up
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Seriously, ask for the toy. When you get older, then join us and have a ball creating armor...