Lilacks

I've heard you can't use some types of store bought glitter in wax melts (not in/on outside of candles, it needs to be IN the hot wax when it melts in the warmer) so what type am I looking for? I've heard mica is ok, what about hex glitter? What should I be looking for on the ingredients list in the store? What about food-safe glitter and dust in the baking section, can you use that in wax melts? Thanks!!