The nail polish spreads out into a super--‐thin film, which creates iridescent, rainbow colors on the paper. The Thin film is only a few hundred nanometers thick, about as thick (or thin!) as a soap bubble. The film is slightly thicker in some places and thinner in others. As the thickness of the film changes, so do the colors. The film reflects light differently depending on how thick it is, so you see different colors. White light is made up of all wavelengths, or colors, of light. Wavelengths that are in sync, hitting the front and back of the film, are reflected back to your eyes as bright colors. Different wavelengths are in sync at different parts of the film depending on its thickness. Many beautiful things in nature get their iridescent colors this way—through the constructive interference of light. Bird feathers, butterfly wings, sea shells, and beetles all have nano-sized, semi-transparent layers that create an iridescent effect when they reflect light.