When the nail polish hits the surface of the water, it spreads out into a thin film. This film is only a few hundred nanometers thick, about the same as the wavelength of visible light. When light hits the thin film, some of the light is reflected off the front surface and some travels to the back. Where the thickness of the film matches the wavelength of a color of light, you see that color.
Iridescent things in nature, such as peacock feathers and butterfly wings use a similar mechanism. Scientists are using nanotechnology of thin films to create batteries, solar cells, electronic displays, and other new products.
Mess Kits are single-serving experiments that allow kids to explore scientific concepts at their own pace. Visitors are encouraged to complete as many as they want! See all Mess Kits.