Surface tension driven flow. Dish detergent dropped on food coloring in milk reduces local surface tension, which pulls the dye to the edges.

By Nikita Novik for Spring 2013 Get Wet.
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Surface tension driven flow. Dish detergent dropped on food coloring in milk reduces local surface tension, which pulls the dye to the edges.

Soap lowers the surface tension of milk in the center of a shallow dish, resulting in food dye being pulled towards the edges

Soap reduces the surface tension of milk, driving a flow that mixes in food dye.

Food dye in milk.

Food dye follows the wake of a finger in milk.

An upside-down image of a dyed ice cube melting in water illustrates the Rayleigh-Taylor instability.

Food dye falling through water is reflected in the water surface when viewed from below.

Water and glass act as lenses for observation of food dye in water.

Food dye dropped into water exhibits the Rayleigh-Taylor instability, forming vortex rings as it falls.

Food dye exhibits the Rayliegh Taylor instability, forming toroidal vortex rings in a mirrored image.