It's long-lasting, cheaper than the sidewalk chalk you can buy, and easy to make - though potentially messy. Only grown-ups should mix the plaster, as plaster dust is caustic. Protect your work area with old newspapers, and don't rinse plaster down the drain!
YOU WILL NEED:
plaster of Paris
water for mixing
liquid tempera paints
measuring cup and spoons
disposable mixing containers (paper cups)
disposable stirring sticks
You can mix this in 8-oz. disposable cups. The recipe is easily doubled if you have larger containers.
Pour 1/4 cup of cool water into a cup. Add 1-1/2 tablespoons of liquid tempera. Stir. (Buy a set of tempera paints for this. Each jar contains about 4 tablespoons - 2 oz. - of paint. Or experiment with powdered tempera, which makes brighter colors.)
Add 1/2 cup of plaster, and mix well. Pour the mixture into a mold. The plastic trays from frozen manicotti work well. You can also use toilet-paper tubes with aluminum-foil bottoms. Try putting layers of colored plaster in the molds to make multicolored chalk. Remove from molds when chalk is completely dry.
- Adapted from 'The Tightwad Gazette II,' by Amy Dacyczyn (Willard Books, 1995)