The colors of soap bubbles are a classic example of thin-film interference. Just before a soap film breaks it stops showing color because it becomes too thin to produce interference. Ore minerals frequently have iridescent films because of a thin layer of alteration on the surface. This Roman plate has developed a spectacular iridescent finish because of a thin film of oxide on its glaze. The play of colors on an oil slick are also due to thin-film interference.
Shells have softer and more subdued interference colors because of multiple-layer interference.
Scattering and superposition of numerous wavelengths softens the colors. Diffraction Diffraction is closely related to interference. The familiar rainbow play of colors on a compact disk is due to tiny pits roughly a wavelength of light apart. Regular, closely spaced structures are common in the biological world and are responsible for diffraction colors like peacock wings or the brilliant blue of this morpho butterfly. Beetles are almost as popular among insect collectors as butterflies, partly because of their bright diffraction colors.