Every year around Easter, you can find egg coloring kits. There is one to make foiling on egg shells... it's the same material they use for Gold Leafing and Chroming. Here's a video I made to explain it a bit more:
https://www.youtube.com/watch?v=1TVWkE_ke_Y
https://www.youtube.com/watch?v=1TVWkE_ke_Y