Make a Moving Rainbow with Milk and Soap

Turn a plate of milk into a moving rainbow with whole milk, food coloring, dish soap, and a cotton swab. Add the color to the center, touch it with the soap-coated swab, and keep the swab still—the color should race outward and swirl around the plate. Do not drink the mixture. 1

Dish-soap molecules spread through the milk and interact with its water, fat, and protein molecules. That motion creates currents that carry the food coloring into the visible patterns. Try the experiment again with another type of milk and compare how the movement changes. 1