To make an easy homemade air hardening clay, place 2 cups baking soda, 1 cup cornstarch and 1 1/2 cups water in a pan and mix until smooth. Heat the mixture over medium heat and stir to boiling. Blend until it's the consistency of mashed potatoes. Place onto a plate and cover with a damp kitchen towel; let cool. Knead to pliability on a work surface dusted with cornstarch.
Cornstarch and baking soda create a smooth, flexible clay that can be left white and painted upon hardening or tinted with food coloring while wet.
To make a baking clay that is ideal for ornaments, combine 1 1/2 cups water, 1 cup salt, 1 teaspoon powdered alum and 4 cups all-purpose flour. If making ornaments, leave the dough at a thickness of approximately 1/2 inch. Form into the desired shape and bake the dough at 250 degrees Fahrenheit on an ungreased baking sheet for 30 minutes. Turn the items over, and bake for an additional 90 minutes or until hard and dry. Use sandpaper to smooth the ornaments before decorating and varnishing.
For Kool-Aid play dough, mix together 2 packages of unsweetened Kool-Aid, 2 1/2 cups all-purpose flour, 1 tablespoon cream of tartar and 1/2 cup salt. Add food coloring for additional color.