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Mother of Pearl (sea shells)
Snail and abalone shells, nested together.
The wings of Blue Morpho butterfly and the surface of the mother of pearl, sea shell, all share a similar mode of coloration: iridescence. The apparent bend of the light comes from interference caused by small surface grooves on the surface. There are approximately 4 striations on one micrometer of Blue Morpho wing, and they are supposed to be made of chitin, the same material marine creature's shells are made of.
The same idea of in or out of phase applies to the sea shell, but there a phenomenon called thin film interference that causes the coloration. The symmetry and sizes of various surface grooves will be observed with SEM using a backscatter imaging technique. Comparisons to known wavelengths of certain light will be used to verify the results and theories proposed.
Cross section of a piece of a sea shell. It is made of chitin. one layer is highlighted in yellow.
The sea shell shows an other mode of iridescence, clearly demonstrating the thin film model. Here waves of light are slowed down by the thin layers of chitin, which are layer on top of each other. If the wavelength of light is refracted (slowed down) by the change in traveling medium, from air to chitin, some wavelengths of light are reflected off the bottom surface of the thin film, and placed back in phase with light that has not penetrated the thin film, but reflected off the top surface. This particular piece displayed a blue iridescence, but other sections of the shell, displayed a range of colors. The color's displayed are dependent on the thickness of the layer of chitin or its index of refraction, which is just how much a material slows down light as it enters.
