Make borax solution. Combine two tablespoons of warm water and 1/2 teaspoon of borax powder. Stir to dissolve the borax. Add food coloring, if desired. You’ll have enough to make seven or eight balls.
Use a different bowl for each ball. Pour in one tablespoon of glue. Add 1/2 teaspoon (2.5 mL) of the borax solution and one tablespoon of cornstarch. Do not stir. Allow the ingredients to interact on their own for ten to fifteen seconds.
Then stir them together to fully mix. Once the mixture becomes impossible to stir, take it out of the cup and start molding the ball with your hands. The ball will start out sticky and messy, but it will solidify as you knead it. Once the ball is less sticky, go ahead and bounce it!
WHAT TO EXPECT
Your ball will solidify and become bounceable.
WHAT’S GOING ON?
Polymers are molecules made up of repeating chemical units. (By the way, a single one of those units is called a monomer.) Glue contains the polymer polyvinyl acetate (PVA), which cross-links to itself when it reacts to being combined with borax.