STEM Activity: Homemade Chalk

Did you know that you can turn everyday kitchen items into creative tools? Turning liquids into a solid is a great way to observe science in action.

Whether you illustrate a scalable mural, create a vibrant obstacle course or jump into a classic game of hopscotch, homemade chalk holds endless possibilities. Get ready to crush, mix and mold your own colorful sidewalk chalk while exploring chemistry!

Materials Needed

• Eggshells
• Flour
• Food coloring
• Measuring spoons
• Mixing bowl
• Mortar and pestle (optional)
• Parchment paper or silicone molds
• Spoon
• Water

Step-by-Step Instructions

1. Collect the eggshells from six eggs. Remove any leftover membrane from inside the eggshells and allow them to dry out for at least 24 hours. This will make it easier to crush them into powder.
    
2. Once fully dried, crush and grind the eggshells into a fine powder using a spoon or mortar and pestle.
    
3. Mix 1 tablespoon of eggshell powder with 1 tablespoon of flour.
    
4. Slowly add 1 to 2 teaspoons of water. If the mixture is too dry, add water as needed. If the mixture is too wet, add eggshell powder until the mixture reaches an ideal consistency. Think of pancake batter — thick, smooth and free of lumps!
    
5. Add about two to three drops of food coloring. Notice how the color changes as you mix! To create a darker color, include a few extra drops of food coloring.
    
6. Mix until a moldable paste forms.
    
7. Shape the paste into any form you like! Press it into silicone molds or wrap it in parchment paper to form sticks. If needed, ask an adult to help press the mixture firmly so that it holds its shape.
    
8. Allow your mixture to dry for at least 48 hours before using it. While you wait, think about what you might like to write or draw with your homemade chalk!

What Are We Discovering?

As you continue to explore the exciting world of STEM, you will discover that all kinds of materials can be combined in unique ways to create something new and useful. Eggshells are made of mostly calcium carbonate, a compound that also is found in limestone, snail shells and even coral reefs. When you crushed the eggshells into a powder and added water, you changed the size of the eggshell particles and the material’s state of matter. After the mixture dried, it became a solid that could be used as chalk!

Chalk might seem simple, but improving its quality takes careful experimentation. National Inventors Hall of Fame^® Inductee Edwin Binney, working with his cousin C. Harold Smith through their company Binney & Smith, developed the first dustless white chalk. His company tested materials and improved how they were made. Much like Binney, you made your chalk creation with patience and persistence. Keep experimenting with your homemade chalk recipe to see how you might change its texture or color!

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