Interesting. I haven’t done casting (only fusing & slumping) but experimenting can be fun when there’s time/money for testing I find that even with the best planning there’s always an element of “testing” since it seems the technical demands of every design vary widely.
I believe I’ve ordered my mica from DelphiGlass.com. I’ve used “Super Bronze”, “Inca Gold”, “Super Sparkle” and “Magna Pearl Silver”. After reading on the web and in books by those with extensive experience I decided to stick to what is known to survive in the kiln. (I do have Pearlex and Mona Lisa Metal powders but not for kiln use so you’d have to test those yourself