Oh how I wish I was better at photographing, especially where sparkle is involved. You'll have to trust me that these both have more sparkle in real life and I hope you try it so you can see for yourself. I started by goofing around with the starfish bath bombs below. They were plain white which is the way I usually leave them. I added a little gold mica to a spray bottle of rubbing alcohol and sprayed the bath bombs. To avoid a lot of mess put the bath bombs is a box before spraying :) The result is a pretty shimmer as well as a bit of colour.
The bath bombs above (I seem to be writing this backwards) were sprinkled with some cosmetic glitter, I did this right after I made them so before they dried. I did spray the bath bombs with some plain rubbing alcohol to kind of set the glitter and they have lots of sparkle! The glitter is iridescent so it goes different colours. If you go to the cosmetics counter looking for glitter you want a mineral type of eye shadow that is loose, you should be able to shake the container and see it move.
Let me know if you try it! Thanks for looking!