Painless, and hopefully profitable for the cosplay crowd out there. I have to cast a large quantity of half-dollar sized dome jewels for Nia, and the experience has been kinda fun, so I thought I'd share it with you all. ^^
Thanks to HCC Cosplay for inspiring/instructing me to make them, though I found my own method, which is what this tutorial illustrates.
Aaaand thanks to ~spiked-stock, who pointed me in the direction of that site AND is keeping me sane while I make my Nia costume. x3 And is the best sewing teacher ever--I crashed her room for five hours the other night to make my skirt.
Hope this is helpful! Post if you have any questions!
Hmm, this may work if you let each individual layer completely cure before pouring the next one? However, you're bounded by 'gravity', if that makes sense--you would pour a partial color into the gem mold, and it would fill the bottom. Then the next layer would fill it and they would go from the 'front' to the 'back' of the jewel. This might look neat for spherical gems, though you might get a 'muddy' color looking through the first color because it would have every color behind it (and form kind of a multi-color brown). But, it would allow you to have 'rings' of color coming out from the center! Layering the colors wouldn't work with any other shape, methinks.
I would imagine you can do that! Keep in mind that the resin produces an exothermic reaction, so the resin may stick to the silicone mold--just make sure you use lots of mold release or some other form of barrier, or in the worst case scenario destroy the mold to peel it off at the end. I would run a test first!