Many birds have the ability to instantaneously adjust their color so their coloration never loses its vividness with age, new research finds.
The natural tech could someday be applied to more eco-friendly paints and to clothing so they would never fade.
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"Current technology cannot make color with this level of control and precision - we still use dyes and pigments," co-author Andrew Parnell of the University of Sheffield said in a press release.
"Now we've learned how nature accomplishes it, we can start to develop new materials, such as clothes or paints, using these nanostructuring approaches. It would potentially mean that if we created a red jumper (sweater) using this method, it would retain its color and never fade in the wash."
Bird feathers are made of a nanostructured spongy keratin material, which is exactly the same kind of material human hair and fingernails are made from. As a result, researchers for many years thought that bird feathers were just colored with chemical pigments known as melanins. These are what color human hair.
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Prior research on feathers has since showed that many have structural color in addition to coloration from natural pigments. Similar to how a clear prism can appear multi-hued due to refraction of light, so too can feathers appear colorful just due to their structure.
For the new study, published in the journal Scientific Reports, Parnell and his team used X-ray scattering at the ESRF facility in France to examine the feathers of a blue jay. They determined that the birds could fine-tune their hues all along the length of a single feather. They do this by manipulating the size of holes in the sponge-like keratin material.
The scientists explained that when light hits a feather, the size of the holes determines how the light is scattered and therefore the color that is reflected. Larger holes mean a broader wavelength reflectance of light, creating the color white. A more compact structure results in the color blue.
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Unless a bird with structural color was grey to begin with, this means that such birds never go grey with age. The process also prevents color changes due to diet.
Birds without much structural coloration, such as seagulls, have less adjustable colors as a result. Seagulls that eat a lot of farm-raised salmon, for example, actually start to turn light pink over time. The salmon are fed artificial carotenoid sources, which transfer over to the birds. These chemicals, called carotenoids, can lead to brightly hued feathers.
The jay, macaws, peacocks and other birds with structural coloration are not as vulnerable to color changes, which is exactly the property most of us want when buying products like house paint and clothing.
Co-author Daragh McLoughlin of the AkzoNobel Decorative Paints Material Science Research Team said, "This exciting new insight may help us to find new ways of making paints that stay brighter and fresher-looking for longer, while also having a lower carbon footprint."
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The new study also helps to explain why the color green so often looks iridescent when it arises from structural color. Think of the shimmery greens of a peacock feather or certain beetles.
"This is because to create the color green, a very complex and narrow wavelength is needed, something that is hard to produce by manipulating (the) tune-able spongy structures," Parnell explained.
"As a result, nature's way to get round this and create the color green - an obvious camouflage color - is to mix the structural blue like that of the Jay with a yellow pigment that absorbs some of the blue color."