Create a rim to prevent your Plaster of Paris escaping using the paper to form a cylinder around the plastic lid.
Soften the Plasticine and create a flat shape, place this inside the lid.
Using a shell press carefully into the Plasticine and then remove. This has made a mould fossil. Now it's time to finish the fossil process and create the cast fossil.
In a small plastic cup mix up the Plaster of Paris according to the instructions.
Pour or spoon the mix into the mould the shell has produced.
Allow to harden till your Plaster of Paris is solid.
Peel away the Plasticine from the plaster cast.
You now have a cast and mould fossil that you have created.