Whitening Sand Dollars for Use in Crafts

They'll also bleach out in the sun.

I would soak them in bleach for 10 minutes and see how they look. Be sure to wash them thoroughly with mild dish soap or baby shampoo after the bleach soaking.

Put them in a sink or plastic dishpan, cover with warm water, add 1/2 cup bleach and some more warm water to mix the bleach around. If all the discoloration doesn't soak out, repeat. If you are worried about doing this, just try one sand dollar to start with.