Make sure you seal your foam before you paint-- the foam will just suck up the colour and not get that nice glossy, metallic sheen otherwise.
As for the jewels, you might want to look into resin casting tutorials. It's a bit of an involved and slightly expensive process, but then you can make any shape of jewel in whatever colour you want!
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- Suzuha Amane (Steins;Gate): 25% (Wig Work) Katsucon 2015
- Magic Armor Link (LoZ: Twilight Princess): 15% (Patterning) Katsucon 2015
- Emperor Lelouch (Code Geass): 2% (Planning) Katsucon 2015
- Hilda, Player Character (Pokemon Black): 18% (Sewing) ?????