Mold and Cast Fossils

Our fossil unit is all about learning how fossils form, where we can find them, and turning into paleontologists. Part of that is getting our hands dirty, carefully digging up fossils. Another part is making those fossils to dig up! For this, we looked at mold and cast fossils that can easily be made out of our fossil salt playdough.

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 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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