Use a butter knife to scrape the eyeshadow from the compact and onto a piece of paper. Then chop the eyeshadow up - you don't want any big clumps, because those will be trickier to mix into the polish.
The eyeshadows I'm using are 4 oz each. Using the whole 4 oz gave a highly pigmented opaque polish, while using half the eyeshadow gave a really sheer polish (shown on my thumb). Both photos are shown using only one coat.
Repeat the same steps for glitter nail polish!