Sand and Cornstarch Modeling Dough

3 cups sand
1 1/2 cups cornstarch
3 tsp alum
2 1/4 cups hot water
food coloring

Mix sand, cornstarch, and alum in saucepan. Add hot water and food coloring. Cook over med. heat until mix thickens. Remove from heat and knead until smooth. Store in air tight container.