The stunningly iridescent colours of abalone shells come from light diffraction through the nacre in the shell. The nacre, also known as mother-of-pearl, is a composite material found inside many mollusc shells, and is what gives them their shiny quality. The nacre is arranged in tiny tiles, and the light bouncing off of them refracts different colours depending on which angle the shell is viewed from. This light interaction is an example of thin-film interference, a phenomenon in which light waves, bouncing off of both the top and bottom of a thin film (in this case the abalone’s nacre tiles), cause the light waves to interfere and overlap, thus creating the beautiful iridescence shown here.