Let me start by saying this is not my original idea, I think the first time I ever potato stamped was back in grade school, but Ben's class was having a Valentine's Day party and I volunteered to come up with a craft idea. I decided it would be fun to make bookmarks so I grabbed some card stock, cut it into strips, gathered ribbon and stamp pads and some foam heart stamps for the class to decorate their bookmarks. Then I remembered using the potato stamp idea back when I was a Pre-K teacher, and decided to carve a few different designs, I like to work with russets - they are sturdy and usually larger which makes for a nice carving surface. After some trial and error I found that a serrated grapefruit spoon comes in handy for scooping out the insides of any carved areas. Because the party was in the morning I went ahead and carved my potatoes with a paring knife the night before- if you do this make sure to soak the potatoes in cold, salted water or else they will turn pink. Drain and pat dry before using.
I had the class use ink pads (also works well with paint but we only had about 15 minutes, not enough time to dry) and the natural moisture in the potatoes made a rather beautiful watercolor effect, especially when more than one color was used.