How to Make Fossils Using Plaster of Paris

Co-authored by Amy Guerrero

Last Updated: January 5, 2023 Fact Checked

Making fossils is a great way to get your child involved in science and history in a creative, fun fashion. It's cheap and easy to create your own replicas with a minimum of skill and material. Here's how to get started.

Method 1

Method 1 of 2:

As An Imprint

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1
Gather your materials. This can get a little messy (especially if there are children around), so lay down some newspapers, put away any objects you don't want to get gooey, and grab your essentials. You'll need:
- A small natural object (shell, leaf, bone, etc.)
- Petroleum jelly
- Plaster of Paris
- Water
- Small disposable dish or Tupperware container (such as a margarine tub)
Any object from nature works -- shells, leafs, and animal bones are all good choices. If you do choose a leaf, make sure it's not dry and crackly. It must also fit in your container!^{[1]
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This will keep the object from sticking to the plaster when you try to remove it. Coat it thoroughly!
4
Mix plaster and water in a bowl. Follow the directions on the plaster of Paris packaging. Mix them together thoroughly and let the concoction sit for a few minutes without stirring.^{[2]
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- You should need about 2x more water than plaster, but you can adjust the ratio as you see fit.
Be careful not to push too hard! Now your part is done; all it has to do is dry. Set it aside and revisit it tomorrow; drying will take at least one day.
After you've waited 24 hours, pop your natural item out of the plaster of Paris and voila! There's your fossil! It's just like a shell was enveloped in soil for thousands of years, disintegrated, and left behind this image.^{[3]
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Method 2

Method 2 of 2:

As A 3D Object

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1
Clean the area. You'll be working with modeling clay and plaster, so, needless to say, this isn't the cleanest of projects. Lay some newspapers down and let's get started. You'll need:
- Plaster of Paris
- Water
- Modeling clay
- Petroleum jelly
- Small natural objects such as sea shells
- Paper cups
- Plastic spoons
- Newspaper or paper towels
Use 1 part plaster of Paris to 2 parts water and mix well in a paper cup with a plastic spoon. Let it sit while you work with the clay.
Generally, leaves, shells, branches, or bones work best. Just make sure you have enough clay and plaster to cover it.
This will be what your object rests and forms an impression in. It needs to be kneaded until it can cover the area of your object.^{[4]
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5
Coat the object with petroleum jelly. Firmly yet slowly press it into the modeling clay to make an impression. The petroleum jelly prevents it from sticking to the clay, so be generous.^{[5]
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- Remove the object carefully to create a mold in the shape of the item you used.
6
Fill the impression left by your object with plaster of Paris. Smooth the plaster to the level of the clay to form a flat surface.^{[6]
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- Place your clay and plaster mold on a newspaper, paper towel, or other disposable surface and allow it to harden. You'll need to wait at least overnight, but 2 or 3 days is preferable and safer.
The shape of your object should be recreated in the plaster, details intact.^{[7]
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Mix the plaster in a separate bowl.

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You can find good snail shells in your yard, in damp and dark areas.

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