|1. In a saucepan, stir baking soda, cornstarch and water over medium heat until smooth. Stir constantly until mixture is very thick and looks smooth again (about 4 minutes, start to finish).
2. Remove from heat to a plate. Let dough sit until just cool enough to handle. Divide into equal parts. Add food coloring, a drop or two at a time.
3. Knead in color as if you were kneading bread dough. Color blends more quickly into warm dough.
4. Do not store until it is fully cool. Then, keep in an airtight container in the fridge - in the butter compartment or somewhere on the door, where it isn't as cold. The homemade clay is odorless.