One summer when I was in high school we went Maine on vacation and I found these sand dollars on the beach. I've had them for about 15 years now, so I decided it was time to find a project for them.
First though, I had to clean them up. They were a little grey, so I soaked them in bleach and water. I forgot to take a "before" picture, so here's a picture after they'd been soaking a few minutes:
Quite an improvement, though they look more uniformly white in the first picture than they actually turned out. They are very small. The smallest is about the size of a dime and the largest is about the size of a quarter. I have yet to come up with a project for them.