This recipe yields two batches of pendulum-pen paint.
In a medium pan over medium heat, mix 1 cup cornstarch and 4 cups water, stirring constantly until thickened, about 5 minutes.
Remove the pan from the heat and continue to stir until smooth. Divide the batch in half.
Stir 2 tablespoons tempera paint and 1 1/4 cups water into each portion.