6 eggshells (washed thoroughly)
1 teaspoon very hot water
1 teaspoon flour
Put eggshells in a electric blender and reduce to fine powder. You can also use a mortar and pestle or a rock on a board. Pick out any remaining big shell pieces and discard. Put water and flour in a bowl and mix until a paste is formed. Add 1 teaspoon of shell powder and mix until well combined. You can also add food coloring or tempera for colored chalk. Roll into a chalk-like stick. Wrap tightly in a paper towel. Let dry for 3 days until hard.