Next time you have scrambled eggs, an omelette or do some baking, save the eggshells and use this activity to turn them into homemade pavement chalk!

What you need:

• 6 clean eggshells

• Flour

• Hot water

• Food colouring

Why buy chalk when you can make your own with just 4 ingredients?

What to do…

1. Make sure to clean your eggshells thoroughly and try to gently remove the membrane inside the shell.

2. Once completely dry, grind the eggshells into a fine powder using a food processor or mortar and pestle.

3. Stir 1 teaspoon of flour and 2 teaspoons of hot water in a small bowl to form a paste.

4. Add 1 tablespoon of crushed eggshells and 2-4 drops of food colouring to the eggshell paste.

5. Mix to combine.
   We used the back of a spoon and spent some time mashing the paste to ensure it was completely combined.

6. Use your hands to roll the paste into a "chalk stick" shape.

7. Wrap the chalk in a paper towel and leave in the sun until dry (approx. 2-3 days) OR bake at 150C for 90 minutes and leave for 1 day to dry.

The resulting chalk is ideal for creating pavement artworks or leaving positive messages.

The science behind your chalk…

The main ingredient in store-bought chalk is calcium carbonate, which is a form of limestone. Calcium carbonate (CaCO3) is the chemical that lets us draw on the pavement with a piece of chalk.

Eggshells also contain calcium carbonate which is why you can turn them into chalk.

As an experiment, try drawing on the pavement using both store-bought and homemade chalk. Which worked best? Do you have a hypothesis as to why?

Did you give it a go?

Send us a photo of your chalk and what you drew and you might find your creation featured in a future issue of Upstart magazine… AND win a prize!