these two recipes come from a book called SCRIBBLE COOKIES by Mary Knoll
I haven't tried them personally, but looks like they could work.
CORNSTARCH AND BAKING SODA
Combine: 1 cup cornstarch, 2 cups baking soda, 1 1/4 cups water in a pan over
medium heat, stirring constantly until thick like dough.
Food coloring may be worked in when cooled slightly, on a breadboard or ona
piece of foil (personally, I add food coloring in the water before cooking
when I make playdough)
Keep covered. Roll, cut, model in small shapes.
CORNSTARCH AND SALT DOUGH
Mixture: 1 cup salt, 1 cup cornstarch, 1/2 cup boiling water and food
coloring or termpera paint.
Mix over low heat, stirring until mixture is too stiff to stir. When cool,
knead until smooth. Model, dry and paint.