Love the fossil matching! Fossil Matching - Use a self-hardening clay: I personally like Marblex Self-Hardening Clay, which is a natural air-dry clay. I get it at Hobby Lobby or a school supply catalog. Collect a set of objects and press each one into a piece of clay to make an impression. Let the clay dry completely and put the fossils in a container along with the objects. Children match the objects to the fossils.