Mix 2 tablespoons of baking soda with 1 tablespoon of white vinegar in a mixing bowl. Let it sit for a minute until the mix no longer fizzes.
Add 1/4 teaspoon glycerin or light corn syrup and 1 tablespoon of cornstarch to the vinegar and baking soda mix in the bowl. Mix well.
Pour the concoction into the small containers you would like the paint to set in. Egg carton cups, baby food jars with lids, bottle caps or paint pans make great watercolor containers. Place the mix in several containers, as each one will be used to make a separate color. Fill the containers only halfway
Add 5 to 10 drops of food coloring to each paint container and mix thoroughly. Make sure to add lots of color, because watercolor paints lighten as they dry. For deeper colors, try adding drink mix powder or coloring paste to the paint mix. Create different paint colors by blending several food colorings in the paint mixes.
Let the paint set overnight before use; it will naturally harden. When the paint is ready, dab a wet paintbrush across the paint to make it ready for use.