Boil 2 cups of sugar and 1 cup of water to make syrup.
Mix 4 tablespoons of baking soda and 2 tablespoons of white vinegar into a bowl. Continue until it stops fizzing.
Add the syrup and 2 tablespoons of cornstarch into the mixture until it has a uniform consistency.
Pour the mixture into an empty egg carton, filling each compartment about a third of the way.
Place five to 10 drops of food coloring into the mixture until you reach the desired color.
Mix the food coloring well.
Paint on watercolor paper after the paint settles overnight.