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If you go looking for the blue in a peacock's feathers, you won't find it

Posted by Kevin Hartnett July 8, 2014 04:13 PM

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Over the last year, Ideas has featured several stories on the elusive nature of color—how hard it is to define in terms we all agree on, or to pin down exactly where it comes from (here and here). Now, a story in the current issue of Harvard Magazine offers particularly head-spinning evidence of color’s surprising nature, taking as its starting point the mysterious blue in the feathers of a tropical bird.

Most colors in nature, and in the manufactured world, begin as chemicals. In plants, molecules of chlorophyll absorb most wavelengths of light, but bounce the green ones back out (in a sense, pine trees appear green due to the one kind of light they don’t in fact contain). There is, however, another way to be colorful.

As journalist Katherine Xue explains, Harvard chemical engineer Vinothan N. Manoharan studies what are known as “structural colors”—colors that are produced in nature by the shape of a surface, rather than its chemical content. A peacock’s tail feathers, for example, contain microscopic ridges, which interfere with light, causing some wavelengths to cancel each other out, and others to be amplified, resulting in the birds’ signature iridescent blue color (the narrow grooves on a compact disc have the same effect). One fun consequence of producing color this way is that it’s easy to make it disappear: The Harvard Magazine article notes that if you grind up a peacock’s feathers, there’s no blue at all in what’s left behind.

Chemical colors, like the ones often used in paints or fabric dyes, fade over time, as ultraviolet light breaks down their molecular structure. Structural colors, however, have staying power. Manoharan is working on creating plastic-filled microcapsules that mimic the surface of another bird’s feathers—the bright blue, tropical cotinga. By manipulating the density of the capsules, his research team can change which wavelengths of light the capsules amplify, and thus which colors appear before our eyes. Aside from their potential practical implications, structural colors are also a clear reminder that color exists as a transaction between objects, not a thing unto itself—more like the sound a tuba makes than a piece of brass sitting on the table.

Image via Wikimedia Commons.

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About brainiac Brainiac is the daily blog of the Globe's Sunday Ideas section, covering news and delights from the worlds of art, science, literature, history, design, and more. You can follow us on Twitter @GlobeIdeas.
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Brainiac blogger Kevin Hartnett is a writer in Columbia, South Carolina. He can be reached here.

Leon Neyfakh is the staff writer for Ideas. Amanda Katz is the deputy Ideas editor. Stephen Heuser is the Ideas editor.

Guest blogger Simon Waxman is Managing Editor of Boston Review and has written for WBUR, Alternet, McSweeney's, Jacobin, and others.

Guest blogger Elizabeth Manus is a writer living in New York City. She has been a book review editor at the Boston Phoenix, and a columnist for The New York Observer and Metro.

Guest blogger Sarah Laskow is a freelance writer and editor in New York City. She edits Smithsonian's SmartNews blog and has contributed to Salon, Good, The American Prospect, Bloomberg News, and other publications.

Guest blogger Joshua Glenn is a Boston-based writer, publisher, and freelance semiotician. He was the original Brainiac blogger, and is currently editor of the blog HiLobrow, publisher of a series of Radium Age science fiction novels, and co-author/co-editor of several books, including the story collection "Significant Objects" and the kids' field guide to life "Unbored."

Guest blogger Ruth Graham is a freelance journalist in New Hampshire, and a frequent Ideas contributor. She is a former features editor for the New York Sun, and has written for publications including Slate and the Wall Street Journal.

Joshua Rothman is a graduate student and Teaching Fellow in the Harvard English department, and an Instructor in Public Policy at the Harvard Kennedy School of Government. He teaches novels and political writing.

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