Mold and Cast Fossils

Our fossil unit is all about learning how fossils form

Where can we find fossils?  To learn more, let’s turn into paleontologists. That means getting our hands dirty and carefully digging up fossils.

If you don’t have fossils (or animal bones) in your backyard, or just want to learn about how mold and cast fossils are made we can use our fossil salt playdough.

Making mold and cast fossils

The hardest part of making mold and cast fossils is deciding what to use to make the first mold.

The options are endless. Local seashells, barnacles, or dead crab legs are a fun natural idea. So are small animal bones if you are landlocked – you can even have a roast chicken for dinner, boil and dry the bones that night, and mold the bones the next day!

If the idea of animal bones or shells as specimens for your mold and cast fossils isn’t up your alley you can dig up (or buy) dinosaur toys, little skeletons, Lego people, small plastic animals, the sky is the limit!

I find it best to let the kids go hunt for whatever they want to fossilize.

As long as it fits a certain size so we aren’t molding something as big as a brick. Not that it isn’t possible to mold something that large, but it would take up a ton of the fossil dough.

Once you have your desired items you can just press them firmly into a ball of the bone dough, and remove. Voila! You have a mold fossil for your collection! Then you just bake the mold at 150F for an hour or let it dry overnight.

To make a cast fossil press a ball of dough into your mold fossil and left dry!

how do you make mold and cast fossils

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