December 21, 2015

Nature's unique way of controlling colour explains why birds never go grey

(December 21, 2015)

*  Birds generate their colour using structure, not dyes and pigments
*  The jay is able to change the colour of its feathers along the equivalent of a single human hair using a tuneable nanostructure
*  This discovery may lead to synthetic structural colour that could be made cheaply and used in paints and clothes that will not fade like dyes and pigments.

Birds use sophisticated changes to the structure of their feathers to create multi-coloured plumage, using a process that could pave the way for the creation of paints and clothing colours that won’t fade over time.

Using X-ray scattering at the ESRF facility in France to examine the blue and white feathers of the jay, researchers from the University of Sheffield found that birds demonstrate a surprising level of control and sophistication in producing colours.

Instead of simply using dyes and pigments that would fade over time, the birds use well-controlled changes to the nanostructure to create their vividly coloured feathers - which are possibly used for jays to recognise one another. The jay is able to pattern these different colours along an individual feather barb - the equivalent of having many different colours along a single human hair.

The jay’s feather, which goes from ultra violet in colour through to blue and into white, is made of a nanostructured spongy keratin material, exactly the same kind of material human hair and fingernails are made from.

The researchers found that the jay is able to demonstrate amazing control over the size of the holes in this sponge-like structure and fix them at very particular sizes, determining the colour that we see reflected from the feather. This is because when light hits the feather the size of these holes determines how the light is scattered and therefore the colour that is reflected. As a result, larger holes mean a broader wavelength reflectance of light, which creates the colour white. Conversely, a smaller, more compact structure, results in the colour blue.

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