Soap bubbles and other thin films are colorful thanks to wave interference across their tiny thickness, but you may have noticed that only some colors appear. Others, like red, seem to be missing. In this video, Dianna digs into the details of wave interference and color theory to explain why we don’t see pure colors in a bubble.
As she points out near the end of the video, the way to make a red bubble is to shine purely red light on the bubble, but even then, you’ll see stripes on it related to the light’s wavelength. Scientists actually use this property to measure the thickness of tiny air gaps between a droplet and a surface. (Image and video credit: Physics Girl)