V.D.
i think this might be what your talking about, i found it on a kids art website.
BAKING CLAY
1 cup salt
1 1/2 cups warm water
4 cups all purpose flour
Stir the salt into the warm water. Let cool. Add flour and knead for 8-10 minutes. For colouring the dough, add food colouring or powdered tempera paint to the salt and water - before adding the flour. Create figures and bake at 325 degrees F for 30 minutes to one hour (until all the moisture is gone). Paint creations when cool. You can also seal the complete work with a non-toxic water-based sealer.