Mix:
1/2 cup cornstarch
1/2 cup salt
3/4 cup flour
Add:
warm water to make into a dough ball
The dough can be rolled, formed, or used to press shells, rocks, or other natural found objects into. Let the dough air dry, turning each day until dry or microwave one minute on each side. It may be necessary to adjust the microwave time according to the thickness of the dough and microwave temperature. The dry dough can be painted with tempera paint.
References / Source:
Longhorn Council