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Candle-wax fossils: Casts, molds, and impressions

Stephen F. Greb
Kentucky Geological Survey


You don't want to mess with plaster to make fossil molds? Would you rather not wait overnight for a fossil you make to dry? Here's a simple solution. Students make impressions and molds in clay and then, with the help of their teacher, make casts with candle wax. After the wax dries, students pull back their “fossils.” You can see examples of fossil impressions at the Kentucky Geological Survey's pictures of different fossil types. This activity should only be done with a teacher or parent because of the candle flame.

Grade Level


Can be done as a demonstration for younger elementary ages, but for safety reasons, teachers should handle the candles and hot wax, not students.


30 minutes in class

Materials :

Large candle or candles (one per adult supervisor)


Objects to make fossils of such as small sea shells, leaves, twigs, feathers, coins, buttons, etc. (flatter or low-relief objects work best for this activity)

Modeling clay to make impressions

First Aid kit or ice (just in case)

Activity worksheet


Fossils are any evidence of ancient life preserved (usually) in stone. There are many types of fossils and many different ways that fossils form. Most fossils are not the actual body parts of the original organisms. Rather they are altered remains, impressions, molds and casts of parts of the organisms. A mold is the impression and void (space, hole) that an organism or organism's body or body part leaves in the sediment. An impression of the outside of the object can leave an external mold in the sediment.  If the object is filled with the same sediment that surrounds the object, an internal mold can be left on the sediment inside the object. If the buried object dissolves and leaves a space or void and  the void is filled with minerals carried in groundwater through the sediment, then a cast is formed.  A cast is the material that fills the void. A cast is made of different material than a mold. Both casts and molds are types of fossils. Sometimes the mold and cast are found together, although molds are more than casts.