A pigment is a substance that swallows particular wavelengths, so the color it gives does not change with the angle. A peacock’s eye does change as you move around it, which means its color does not come from pigment. Where does it come from?
From an arrangement. Inside of the feather, are laid out in periodic layers spaced at about the wavelength of light. Light reflected off different layers travels slightly , so one color reinforces and the others cancel. and you change that difference in path, and with it the color that reaches the eye.
Nature holds almost no blue pigment, so a brilliantly blue feather demands another explanation.
Inside the tiny barbs of the feather, melanin and keratin are arranged in periodic layers, at spacings on the order of the wavelength of light.
Light reflected off different layers travels slightly different distances, so one color reinforces and the others cancel. Having many layers sharpens the selection, and that is where the saturation comes from.
Change the angle and you change the difference in path, and with it the color that reaches the eye. That is the signature of structural color: a pigment looks the same from any direction. The dark melanin adds contrast, the feather combines structure with pigments, and the exact pattern differs between regions of the feather and between peacock species.
wat. The blue of a peacock feather is built from a minute order that filters light, which is why it changes with the angle.
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Structural color can stay intense with no chemical dye, and it inspires coatings, sensors and materials that are hard to counterfeit.
How do we know?
Microscopy revealed the periodic arrangement, and spectrometers measured how the color peaks shift with the angle of lighting and of viewing.
What is still unknown
The feather combines structure and pigments, and the exact pattern differs between regions of the feather and between peacock species.
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Where to next
The wings are blue, and there is almost no blue in them. How?structural color
How does a desert bird carry water home to its chicks?feathers