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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- Pearl (Steven Universe): 34% (Sewing) Winter/Spring 2016
- Labelle (Animal Crossing New Leaf): 96% (Final Details) Katsucon 2016
- Pyrrha Nikos (RWBY): 56% (Weapon Work) Katsucon 2016
- Pyrrha Nikos Weapons (RWBY): 50% (Carving Sword) Katsucon 2015