1. Mix tempera paint, a little at a time,  with the water and stir. (Adding more paint makes mixture goopier.) Make separate batches for other colors.
  2. Mix baking soda and cornstarch in a pot; add the water and paint mixture. Stir over medium heat until dough forms a ball.
  3. Remove from heat and let cool to touch. Knead warm dough to workable consistency.
  4. After play, store in plastic zipper bags until next use.

Flourless DIY Play Dough  photography by Country Woman.