Soap bubble landscape. Close-up of the surface of a bubble of soap showing light interference effects. The swirling pattern and lines of colour occur by light rays being reflected from both the front and back of the thin film of water making up the bubble. The thickness of the film varies across the bubble, affecting the wavelength of incident white light. Silver colour is produced by a film about 70 nanometers thick, gold about 100 nanometers thick, green about 150 nanometers thick and red as the film gets thicker. As the soap film drains vertically under gravity, the top of the film becomes thinner and the bottom thicker. The bubble then bursts.