Making things with plaster of Paris is surprisingly easy and not as messy as you might think. At just a few dollars for a big bag, it's also quite a cheap material. These sand cast fossils are really fun to make for kids of all ages. You can press just about anything into the sand to make a mold so let your imagingation go wild.
Time: 30 minutes plus 24 hours drying time
Age: Any Age
Plaster of Paris
Tub for the mold
Disposable tub to make the plaster mix in
Items to press into the mold (eg small plastic toys, feet, shells etc)
Put at least an inch depth of damp sand into a tub. The tub shape will be the final size and shape of your fossil so choose a larger tub if you want to be able to press lots of different things in, or something small (like a paper cup) if you want to make a small fossil with just one object.
Press items into the sand and then remove again to leave imprints. Let your imagination go wild! Why not try footprints, plastic animals, plastic dinosaurs or sea shells?
We tried a footprint as well as various plastic animals
Mix the plaster of Paris in a disposable container according to the instructions on the packet. We used 2 cups of plaster and added it to 1 cup of water to make two large fossils. Stir well until you have a pancake batter consistency.
Gently pour the plaster onto your sand mold. Don't tip too quickly or you will make indents in the sand as you pour. We poured about a 1 centimetre thickness of plaster but you could choose to make a thicker one
Leave to set for at least a few hours then pop the dried cast out of the tub and rinse the sand off with water.
Ready to rinse off the sand
Some sand will remain encrusted on the surface giving it a grainy finish.
Allow to dry fully for about 24 hours
Our fish gained an extra fin where we poured the plaster a bit too quickly and it made a dent in the sand shape when we poured
The grainy sand finish looks great to give an ancient fossil appearance. If you want to get a smooth finish you could try using modelling clay instead of sand for the mold.
Notes Mixing the plaster of Paris up in a disposable container means you can just throw away the container after the activity. As plaster can harden in pipe work you won't want to pour any wet plaster down the sink. The tub and tin we used for the sand casting were not damaged after we had removed the dried casts. Try not to touch the plaster dust or wet plaster and be careful not to inhale any plaster dust.