I saw this on Pinterest the other day, and I decided I would make it!
Start out with any key you don't want or don't need to use. Paint glue on the top half of it, making sure to cover both sides. (I used tacky glue, but there are probably other kinds of glue you can use)
Then sprinkle glitter over the glue. I used several different colours for mine. When you're done, let it dry a while and then paint over it with clear top coat nail polish. You can put it on a necklace when you're done, which is what I did! Or I bet there are other cool things you could do with it as well! : )