Sometimes when you see a dinosaur skeleton in a museum, you're looking at a cast of the bones, while the real ones remain safely stored away. Try this to make a cast of some bones or other special objects around your house!

You will need:

• modelling clay, plasticine or potter's clay
• a piece of bone (eg. chicken) or a shell
• petroleum jelly or castor oil
• a small brush
• Plaster of Paris

Making the impression or mould:

• Knead the clay or plasticine in your hands until it is soft.
• Press it flat so that it is about 2 cm thick (a rolling pin is suitable for this).
• Brush the bone or shell with oil or petroleum jelly (so that it doesn't stick) and push it into the clay.
• Carefully remove the bone or shell.

The impression of the bone or shell is similar to the impression left by dinosaur bones. Fossils were made when dinosaurs, plants, shells and even insects were covered in mud. They slowly decayed leaving just an impression.

To make a cast:

• Follow the instruction on the Plaster of Paris box.
• Mix small quantities at a time, with water, in a plastic container.
• Pour the plaster into the mould (the plaster will feel warm as it begins to set).
• When the plaster is cold and set remove it from the mould.

The plaster cast is a replica of the original bone. By making a cast you can see what the original fossil looked like.

Try this!

Bury some bones in a box of dirt. Let your friends excavate the box. Can they work out what animal the bones belong to?

Now that you've got your cast, see if you can use it to Create Dino Tracks!