Make a fossil cast: plaster experiment for kids

Materials and mold in 4 steps

You need soft clay, a shell or toy dinosaur, plaster powder, water, a cup, a spoon and a tray to make a fossil cast safely at home.

Press the shell into clay to make a mold, mix plaster with water, pour it into the mold, wait twenty four hours, then lift the cast and clean it gently.

Molds versus casts and museum method

A mold is the hollow print left in rock, a cast is the hard copy that fills it, real fossils form the same way when minerals replace bone or shell over time.

Real museums make plaster copies the same way to study bones, always work on a tray, wash hands after plaster and ask an adult to mix powder and help dig out.

• Molds are hollow, casts are solid.
• Plaster hardens in about 24 hours.
• Brush dust off, do not wash fossils.
• Label each find with date.
• Museums copy bones with plaster.