I was thinking the same, I have got some micas on the shelf, I need to find time to try this. You can mix glitters, so why not micas? And I guess eye shadow is not very different? You have some interesting eyeshadow on your mind? DO not forget to take pics!
I've used mac. I've also used sand, glitter from michaels, pearl pigments for candle making, and cheaper eyeshadow. I always put a thin layer of clear on the nail bed first, in case it might stain. And with any new product, I always test myself first to see how it holds up.
I did it today. My mate was booked in so she was guinea pig! Mixed clear nsi with barry m midnight blue. It felt silky when applying like a really smooth texture (bit wierd) but it did set rock hard and the end result was a wicked irredesent dark blue,looked great! Fingers crossed it lasts! If it does then I'm gonna buy half of superdrug!