You do have to make this one ahead of time, but children will love watching you mix this up!
Ingredients
1white vinegar
2Baking soda
1Cornstarch
1/4tspglycerin
Liquid food coloring
Plastic bottle caps from 2-liter bottles
Instructions
Mix vinegar and baking soda in small bowl. When mixture stops bubbling, add cornstarch and glycerin. Mix well. Pour mixture into bottle caps. Add several drops of food coloring to the mixture in the bottle caps. Let dry overnight.