Things You'll Need
Instructions
Fill the large container that you have chosen half-full with modeling clay. This will serve as the base for the mold.
Clean the fossil with a soft brush or a dental pick. Make sure your fossil is free of excess dirt and debris before making the cast.
Press the fossil into the modeling clay. Remove this fossil to make a mold.
Mix up the plaster of Paris, which is typically composed of one part water to two parts powder. Mix well. Let the mixture set for about five minutes.
Pour the plaster of Paris into the mold. Let it set for one hour before removing it from the container.
Remove the cast from the container. Make sure that drying does not occur too quickly. The cast will be completely dry in a few days. Clean off the clay and re-use if desired.