The Peacock Sink
I just had to write because we had a glass sink come out the other day that reminded me of a peacock. I named it The Peacock Sink. There are blue spots in the sink similar in shape and coloring to the ?eyes? in a peacock?s plumage. Though the spots aren?t exactly the same, the deep vivid colors that sometimes change hue are something that Alchemy sinks share with peacock feathers. I wanted to see if I could learn more about the unique way that color works in these sinks by understanding how a peacock feather gets its color.
Peacock feathers and Alchemy sinks get their iridescent color from an optical phenomenon that happens when light hits their surface. Intricate structures in the surface, with details measuring 10,000ths of a millimeter, interfere with incoming light in such a way that specific colors are reflected brighter and others dimmer. It?s called structural coloration.
Most color we see is a result of pigments which appear to be a certain color because they reflect or transmit only the desired wavelengths of light after absorbing all the undesired wavelengths. Colors can only be as bright as that portion of the spectrum that exists in the incoming light. They also perform the same way no matter how the light hits the pigmented surface so the color doesn?t change.
?FeatherLocking? by W R Ogilvie Grant???Trustees of the British Museum 1921.
Unlike pigments, structural coloration can and does change hue depending on which angle the light hits the surface. This is iridescence: where luminous colors seem to change when seen from different angles. It comes from the same microscopic structures. Because this is an optical effect, changing the angle of light changes the wavelength that is amplified. This is why the colors appear to change when you look at these things from different angles or change the angle of illumination. With peacock feathers and butterflies this creates a shimmering effect. Because Alchemy sinks don?t move around the same way these live creatures do, the effect is one of revealing new colors that become more vivid as you change your viewpoint.
I don?t know where the structure responsible for the color in Alchemy sinks is located, but in the peacock feather, the structure is found in the microscopic melanin tubes that make up the barbules attached to the barbs of the feather. The barbs are the pieces that come off the feather?s central stalk, and the barbules are the delicate velcro-like hairs that line the barbs and hold them to the barbs on either side (see drawing). You can?t really see the hairs, and you definitely can?t see the melanin tubes inside them because they?re spaced about 140?190 nanometers (between 1 and 2/10,000ths of a millimeter) apart. That specific spacing is the key to the color.
Scanning Electron Microscope image of peacock barbules from The Physics of Structural Colors by S. Kinoshita, et. al.
Wavelengths of light are roughly between 400 and 700 nanometers and the closeness in size between the barbules? ridges and the actual wavelengths of light is the reason this type of structure can interfere with and change the light. As a matter of fact just the difference between 165 nanometer spacing and 150 nanometer is the difference between yellow and green. Go down to 140 nanometers and that 1/100,000th of millimeter difference is the difference between green and blue.
Closeup of barbules showing collection of colors from different structures within the barbules (images from http://hyperphysics.phy-astr.gsu.edu)
Interestingly, the peacock feathers would appear brown without this specific structure because that?s their pigmented color. Their structural color is a lot brighter and more interesting. Different sections of the feather have structures with the different spacings which creates the overall pattern of color across the feather. One way we know this color isn?t a pigmented color is that a peacock?s feathers temporarily lose their fancy color when wet.
left image from albino-peacock.blogspot.com; right image is closeup of The Peacock Sink
When I searched for an image of peacock feathers, I discovered that the coloring of the eyes in the sink are missing the dark center like the ones on peacocks. The blue color in the eye of the peacock feather is more like the iris of an actual eye surrounding the dark pupil. I?m guessing this evolved as a protective device for peacocks so predators might think they?re seeing lots of animals hiding in the peacock?s plumage. In the sink?s case, no such luck. As far as I know, the only predator of the Alchemy sink is men shaving with very hot water. That?s a story for another article.