Isegoria

Blackbirds, Ed Yong explains, aren’t actually all that black:

Their feathers absorb most of the visible light that hits them, but still reflect between 3 and 5 percent of it. For really black plumage, you need to travel to Papua New Guinea and track down the birds of paradise.

Although these birds are best known for their gaudy, kaleidoscopic colors, some species also have profoundly black feathers. The feathers ruthlessly swallow light and, with it, all hints of edge or contour. They make body parts seem less like parts of an actual animal and more like gaping voids in reality. They’re blacker than black. None more black.

By analyzing museum specimens, Dakota McCoy, from Harvard University, has discovered exactly how the birds achieving such deep blacks. It’s all in their feathers’ microscopic structure.

A typical bird feather has a central shaft called a rachis. Thin branches, or barbs, sprout from the rachis, and even thinner branches—barbules—sprout from the barbs. The whole arrangement is flat, with the rachis, barbs, and barbules all lying on the same plane. The super-black feathers of birds of paradise, meanwhile, look very different. Their barbules, instead of lying flat, curve upward. And instead of being smooth cylinders, they are studded in minuscule spikes. “It’s hard to describe,” says McCoy. “It’s like a little bottle brush or a piece of coral.”

These unique structures excel at capturing light. When light hits a normal feather, it finds a series of horizontal surfaces, and can easily bounce off. But when light hits a super-black feather, it finds a tangled mess of mostly vertical surfaces. Instead of being reflected away, it bounces repeatedly between the barbules and their spikes. With each bounce, a little more of it gets absorbed. Light loses itself within the feathers.

McCoy and her colleagues, including Teresa Feo from the National Museum of Natural History, showed that this light-trapping nanotechnology can absorb up to 99.95 percent of incoming light. That’s between 10 and 100 times better than the feathers of most other black birds, like crows or blackbirds. It’s also only just short of the blackest materials that humans have designed. Vantablack, an eerily black substance produced by the British company Surrey Nanosystems, can absorb 99.965 percent of incoming light. It consists of a forest of vertical carbon nanotubes that are “grown” at more than 750 degrees Fahrenheit. The birds of paradise mass-produce similar forests, using only biological materials, at body temperature.

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