How to Make a Fossil Cast

Making a cast of a fossil is a good way to share your fossil with other people. Often, museums will make casts of their fossils to give to other museums or to individuals who donated fossils they have found. Follow these steps to learn this useful skill.

Difficulty: Challenging

Instructions

Things You'll Need:

• Modeling clay
• Fossil brush
• Dental pick
• Plaster of Paris
• Spoon
• Plastic containers

1. Fill the large container that you have chosen half-full with modeling clay. This will serve as the base for the mold.

2. 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.

3. Press the fossil into the modeling clay. Remove this fossil to make a mold.

4. 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.

5. Pour the plaster of Paris into the mold. Let it set for one hour before removing it from the container.

6. 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.

Tips & Warnings

• If the fossil is three-dimensional (like a bone) you will need to make two casts of the fossil, flip them over and join them together with glue.
• Be sure to follow the instructions for preparation that came with the Plaster of Paris.

Resources

• A Manual of Practical Laboratory and Field Techniques in Palaeobiology