Add 1 tablespoon eggshell powder and mix until a paste forms. Add food coloring if desired. Shape and press mixture firmly into the shape of a chalk stick, and roll up tightly in a strip of paper towel. Allow to dry approximately 3 days until hard. Remove paper towel.
Eggshell chalk is for sidewalks only.
Portion the mixture into a paint palette, muffin tin or similar container and add food coloring. Make the colors dark because drying and use will lighten them. Clean supermarket meat trays can be used for this, too. But make sure these are washed in an antibacterial solution first.