The changing hues of a peacock’s splendid tail feathers have always captivated curious minds. Seventeenth-century English scientist Robert Hooke called them “fantastical,” in part because wetting the feathers caused the colors to disappear. Hooke used the recently invented microscope to investigate the feathers and saw that they were covered with tiny ridges, which he figured might produce the brilliant yellows, greens and blues.

Hooke was on the right track. The intense colors of bird plumages, butterfly wings and the bodies of squid are often produced not by light-absorbing pigments but by arrays of tiny structures that are just a few hundred nanometers wide. The size and spacing of these structures pick out particular wavelengths from the full spectrum of sunlight. The hues are also often iridescent, changing, like magic, from blue to green or orange to yellow, depending on the angle at which we see the animal. And because the colors are produced just by reflecting light rather than absorbing some of it, as pigments do, they can be more brilliant. The blue morpho butterfly of South and Central America can be seen from up to a kilometer away; it seems to shine when sunlight penetrates a tropical forest canopy and bounces off its wings.

Scientists are beginning to understand more fully how the delicately arranged nanostructures of living organisms manipulate light, which in turn is inspiring engineers to mimic the biological designs in new, man-made optical materials. The materials could lead to more brilliant visual displays and new chemical sensors, as well as to better storage, transmission and processing of information.

We know relatively little about how these biological structures evolved, but we are at least learning how they are formed and how they produce fantastical colors. Nature does not have sophisticated technologies such as electron beams that can etch thin layers of material, so it has relied on ingenuity instead. If engineers can master the same art, they might develop cheap fabrics that change appearance like the camouflage of squid or like computer chips that transmit information optically instead of electrically and at blazing speeds. Here we look at some of nature’s tricks for forming structures that create color and the ways inventors are trying to exploit them.

1 Layers on Layers The ridges Hooke discovered on peacock feathers do scatter light, but the bright colors generally come from nanostructures he could not see that lie underneath the surface. The colored feathers of birds and scales of fish and butterflies typically contain microscopic, organized layers or rods of a dense light-scattering material. Because the distance between the layers or rods is roughly the same as the wavelengths of visible light, the structures cause the phenomenon known as diffraction. Incoming light rays of certain wavelengths reflect off the layers and interfere with one another “constructively” or “destructively,” boosting some colors in the reflected light while canceling others. The same process creates the rainbow of colors seen when the shiny surface of a compact disc is tilted back and forth.

In butterfly wings, the reflecting layers are made of the natural polymer chitin, separated by air-filled voids within the hard outer surface (cuticle) of the wing scales. In bird feathers, the layers or rods are made of melanin and embedded in keratin, the protein that makes up our hair and fingernails. The optics industry already uses diffraction gratings made from ultrathin, alternating layers of two materials to select and reflect light of a single color in products ranging from telescopes to solid-state lasers.

The male Lawes’s parotia (Parotia law­esii) bird of paradise employs an ingenious twist on this trick, which Doekele G. Stavenga of the University of Groningen in the Netherlands discovered in 2010. Hairlike barbules on its breast feathers contain layers of melanin spaced at a distance that creates bright orange-yellow reflections. But each barbule has a V-shaped cross section with sloping surfaces that also reflect blue light. Slight movements of the feathers during the bird’s courtship ritual can switch the color abruptly between orange-yellow and blue-green, a change guaranteed to catch a female’s eye.

Technologists have not tried to mimic the effect, but Stavenga imagines that the fashion and automobile industries will eventually try to exploit these color changes. V-shaped microflakes in fabric could make a dress change color as the wearer moves, and such microflakes in paint could make the color of a passing car morph dramatically.

2 The Christmas Tree Effect The butterflies Morpho didius and M. rhetenor obtain their dazzling blue color not from multilayers of chitin but from more complex nanostructures in the wing scales: arrays of chitin that are shaped like Christmas trees and sprout at the scales’ outward surface. The parallel branches of each “tree” act as another kind of diffraction grating. These arrays may reflect up to 80 percent of the incident blue light. And because they are not flat, they can reflect a single color over a range of viewing angles, somewhat reducing the iridescence. Organisms do not always want to change color when seen from different directions.

As Hooke observed with peacock feathers, when water runs over the blue morpho’s wings, it changes the refraction of the light. Different liquids that have different indexes of refraction therefore lead to different color reflections. Researchers at GE Global Research in Niskayuna, N.Y., in collaboration with others at the University at Albany and butterfly wing expert Pete Vukusic of the University of Exeter in England, are developing artificial Morpho-like structures to create chemical sensors that can identify a range of different liquids, taking on a unique color depending on the liquid they come into contact with. They use microlithographic techniques borrowed from the semiconductor industry to carve the structures into solids. The sensors could possibly detect certain emissions at power plants or impurities in drinking water.

3 Light-Bouncing Bowls The bright-green color of the emerald swallowtail butterfly (Pap­ilio palinurus), found widely in Southeast Asia, is not produced by green light at all. The wing scales are covered with a grid of tiny, bowl-shaped dimples just a few microns across. The dimples are lined with layers of chitin separated by air, which act as selective mirrors. The bottoms of the bowls reflect only yellow light, and the sides of the bowls surrounding the yellow center reflect only blue. Our eyes cannot resolve the yellow and blue at such small scales, so our brain sees the combination as green.

Christopher Summers and Mohan Srin­i­vasarao of the Georgia Institute of Technology have copied this method for making color. To create the tiny bowls, they let water vapor condense as microscopic droplets on the surface of a polymer that is setting from liquid to solid. The water droplets pack together on the surface like rows of eggs in a carton, sinking into the film. The droplets evaporate as the polymer sets, creating a surface that has bowl-like dimples. The researchers then deposit thin, alternating layers of titanium oxide and aluminum oxide in each bowl to make a reflector that mimics the natural lining of the butterfly bowls.

Light bouncing off the patterned film appears green. When the film is placed under a set of polarizing filters, however, the yellow light bouncing back from the centers of the bowls disappears while the blue light from the rims remains. This mechanism could offer a distinctive authentication mark on credit cards and bank cards. What would appear as a simple green reflective coating would in fact carry a hidden, polarized yellow and blue signature that would be difficult to counterfeit. Srinivasarao admits, though, that the main reason they are trying to replicate the butterfly’s green color is that “it’s beautiful in its own right.”

4 Nanosponges Another butterfly, the emerald-patched cattleheart (Parides sesostris), creates green color by using a different nanostructure; again, no pigments are involved. Its wing scales sport microscopic, crystalline arrays of holes. These so-called photonic crystals totally exclude light within a particular band of wavelengths, causing that light to reflect. Opal gemstones are photonic crystals made from tiny spheres of stacked-together silica that scatter light, thus giving the stone its iridescent rainbow colors. Photonic crystals can be used to confine light within narrow channels, creating waveguides that could possibly steer light around the tight spaces on computer chips.

Under the electron microscope, the cattleheart butterfly’s wing scales display arrays with a zigzagging appearance—patches of sponge made from chitin with orderly patterns of holes that are around 150 na­no­met­ers or so across. Each patch is a photon­ic crystal set at a slightly different angle from its neighbors. The structure enables it to reflect light within the green part of the spectrum over a wide range of incident angles. Some weevils and other beetles also derive their iridescent color from photonic crystals made of chitin.

Biologist Richard Prum of Yale University and his colleagues have figured out how these photonic crystals grow as young butterfly wings develop. Essentially lipids in the embryonic wing-scale cells spontaneously form a patterned template in three dimensions, and chitin hardens around them. The lipids then break down as the cells die, leaving a hollow matrix with a regular pattern of voids.

Researchers are trying to make similar structures from scratch. For instance, lipidlike molecules called surfactants will form orderly sponges, as will so-called block copolymers. Ulrich Wiesner of Cornell University has used these copolymers to arrange nanoparticles of niobium and titanium oxide into mineral-like “nanosponge” structures.

These porous solids could find a wide range of applications, such as more efficient, low-cost solar cells. Moreover, Wiesner has calculated that nanosponges made from metals such as silver or aluminum could have the weird property of a negative index of refraction, meaning they would bend light “the wrong way.” Such materials, if they can be fabricated, could form superlenses for optical microscopes that can image objects smaller than the wavelength of light, which is not possible in conventional microscopes.

5 Crystal Fibers Animals can sculpt photonic crystals in many ways. The spines of some marine worms, such as Aphrodita (the sea mouse), contain hexagonal arrays of hollow fibers a few hundred nano­me­ters across. These arrays, made from chitin, exclude light in the red part of the spectrum, giving the Aphrodita spine an iridescent red color.

It is not clear if these optical properties have any biological function in the sea mouse. But applications in optical technology certainly exist for such light-manipulating fibers. Philip Russell, now at the Max Planck Institute for the Science of Light in Erlangen, Germany, has heated and drawn out bundles of glass capillaries into thin fibers laced with hexagonally packed holes. If a wider capillary or a solid rod is added into the middle of the original bundle, it creates a defect in the array of holes, along which light can pass while being excluded from the surrounding photonic crystal. This creates an optical fiber with a cladding that is essentially impermeable to light within a particular band of wavelengths.

Photonic crystal fibers “leak” less light than conventional ones, so they could replace the standard fibers in telecommunications networks. They would require less power, thereby eliminating the need for costly amplifiers to boost signals sent over long distances. Conventional fibers become particularly leaky at tight bends, where the reflections that confine the light inside the fiber are less efficient. Photonic crystals do not have this problem, because their light trapping does not rely on reflection. Thus, they should work better in small, confined spaces, resulting in optical microchips that are far faster than the electronic chips in our computers and cell phones.

6 Deformed Matrices To create colors, some creatures form spongy matrices that have a disorderly pattern instead of an orderly one. This structural variation creates the splendid blue and green plumage of many birds that lacks the iridescence seen on the hummingbird or the peacock. Because the spongelike keratin na­no­structures in these cases are disordered, the light scattering is diffuse, akin to the blue of the sky, rather than mirrorlike and iridescent, so the color appears uniform when viewed from any angle.

In the blue and yellow macaw (Ara ararauna) and the black-capped kingfisher (Halcyon pileata), the empty spaces in the matrix of the feather barbs form tortuous channels about 100 nanometers wide. A similar random network in the cuticle of the Cyphochilus beetle gives it a dazzlingly bright white shell. In the blue-crowned manakin (Lepidothrix coronata), the airholes are not channels but are little, connected bubbles.

Yale’s Prum thinks the channels or bubbles are created as keratin separates spontaneously, like oil from water, from the fluid in feather-forming cells during early development. He also thinks that birds have evolved a way to control the rate at which the keratin separates, so the channel or bubble formation stops when the voids reach a certain size. This size determines the wavelength of scattered light and thus the feather’s color.

Diffuse light scattering can be seen in other natural and man-made substances. In milk, microdroplets of fat with a wide size range scatter all visible wavelengths, thus creating an opaque whiteness.

Exeter’s Vukusic has mimicked the Cyphochilus beetle cuticle with random porous matrices of calcium carbonate or titanium dioxide mixed with a polymer, making thin coatings that are brilliantly white. Meanwhile Prum and bioengineer Eric Dufresne, also at Yale, have imitated the disordered sponges of bird feathers by creating films of randomly packed microscopic polymer beads, which have blue-green colors. These approaches could lead to coatings that have strong, highly opaque colors even though they are extremely thin, and the colors would never fade because the films do not contain organic pigments.

7 Reversible Proteins One of nature’s most enviable optical tricks is to produce reversible color changes. Squid in the Loliginidae family use a protein called reflectin to create and alter colors in their skin. The protein molecules are arranged into stacks of plates inside cells called iridophores, which reflect specific colors. Biologists think the color changes serve as camouflage and as communication for mating and displays of aggression.

Daniel Morse of the University of California, Santa Barbara, is studying how iridophores change color. The reflectin proteins crumple into nanoparticles, which form the plates. The plates are sandwiched between folds in the iridophore cell’s membrane. When a neurotransmitter activates a biochemical process that neutralizes the electrical charge of the reflectins, the proteins pack more closely. The change increases the reflectivity of the plates and changes their spacing, altering the color. The change can be reversed if the reflectins regain charge.

Morse thinks he can mimic this mechanism in optical devices, perhaps using reflectins themselves. His team has inserted the gene that encodes a reflectin protein in the longfin inshore squid Loligo pealeii into Escherichia coli bacteria. When expressed, the pro­tein collapses into na­no­particles. The par­t­icle size can be tuned with salts that control the interactions between charges on the proteins. The materials might then swell and contract, altering the reflected wavelengths in response to chemical triggers.

Morse has also developed a polymer that dramatically switches from transparent to opaque in response to electrical voltages, which alter the polymer’s reflectivity and swell the polymer film by drawing in salt. Devices using these materials can be made with simple, low-tech manufacturing methods. His team is working with Raytheon Vision Systems in Goleta, Calif., to turn this material into fast shutters for infrared cameras, thus enabling high-speed “night filming” by detecting heat rather than light. 

This article was published in print as “Nature’s Color Tricks.”

Hooke was on the right track. The intense colors of bird plumages, butterfly wings and the bodies of squid are often produced not by light-absorbing pigments but by arrays of tiny structures that are just a few hundred nanometers wide. The size and spacing of these structures pick out particular wavelengths from the full spectrum of sunlight. The hues are also often iridescent, changing, like magic, from blue to green or orange to yellow, depending on the angle at which we see the animal. And because the colors are produced just by reflecting light rather than absorbing some of it, as pigments do, they can be more brilliant. The blue morpho butterfly of South and Central America can be seen from up to a kilometer away; it seems to shine when sunlight penetrates a tropical forest canopy and bounces off its wings.

Scientists are beginning to understand more fully how the delicately arranged nanostructures of living organisms manipulate light, which in turn is inspiring engineers to mimic the biological designs in new, man-made optical materials. The materials could lead to more brilliant visual displays and new chemical sensors, as well as to better storage, transmission and processing of information.

We know relatively little about how these biological structures evolved, but we are at least learning how they are formed and how they produce fantastical colors. Nature does not have sophisticated technologies such as electron beams that can etch thin layers of material, so it has relied on ingenuity instead. If engineers can master the same art, they might develop cheap fabrics that change appearance like the camouflage of squid or like computer chips that transmit information optically instead of electrically and at blazing speeds. Here we look at some of nature’s tricks for forming structures that create color and the ways inventors are trying to exploit them.

1 Layers on Layers The ridges Hooke discovered on peacock feathers do scatter light, but the bright colors generally come from nanostructures he could not see that lie underneath the surface. The colored feathers of birds and scales of fish and butterflies typically contain microscopic, organized layers or rods of a dense light-scattering material. Because the distance between the layers or rods is roughly the same as the wavelengths of visible light, the structures cause the phenomenon known as diffraction. Incoming light rays of certain wavelengths reflect off the layers and interfere with one another “constructively” or “destructively,” boosting some colors in the reflected light while canceling others. The same process creates the rainbow of colors seen when the shiny surface of a compact disc is tilted back and forth.

In butterfly wings, the reflecting layers are made of the natural polymer chitin, separated by air-filled voids within the hard outer surface (cuticle) of the wing scales. In bird feathers, the layers or rods are made of melanin and embedded in keratin, the protein that makes up our hair and fingernails. The optics industry already uses diffraction gratings made from ultrathin, alternating layers of two materials to select and reflect light of a single color in products ranging from telescopes to solid-state lasers.

The male Lawes’s parotia (Parotia law­esii) bird of paradise employs an ingenious twist on this trick, which Doekele G. Stavenga of the University of Groningen in the Netherlands discovered in 2010. Hairlike barbules on its breast feathers contain layers of melanin spaced at a distance that creates bright orange-yellow reflections. But each barbule has a V-shaped cross section with sloping surfaces that also reflect blue light. Slight movements of the feathers during the bird’s courtship ritual can switch the color abruptly between orange-yellow and blue-green, a change guaranteed to catch a female’s eye.

Technologists have not tried to mimic the effect, but Stavenga imagines that the fashion and automobile industries will eventually try to exploit these color changes. V-shaped microflakes in fabric could make a dress change color as the wearer moves, and such microflakes in paint could make the color of a passing car morph dramatically.

2 The Christmas Tree Effect The butterflies Morpho didius and M. rhetenor obtain their dazzling blue color not from multilayers of chitin but from more complex nanostructures in the wing scales: arrays of chitin that are shaped like Christmas trees and sprout at the scales’ outward surface. The parallel branches of each “tree” act as another kind of diffraction grating. These arrays may reflect up to 80 percent of the incident blue light. And because they are not flat, they can reflect a single color over a range of viewing angles, somewhat reducing the iridescence. Organisms do not always want to change color when seen from different directions.

As Hooke observed with peacock feathers, when water runs over the blue morpho’s wings, it changes the refraction of the light. Different liquids that have different indexes of refraction therefore lead to different color reflections. Researchers at GE Global Research in Niskayuna, N.Y., in collaboration with others at the University at Albany and butterfly wing expert Pete Vukusic of the University of Exeter in England, are developing artificial Morpho-like structures to create chemical sensors that can identify a range of different liquids, taking on a unique color depending on the liquid they come into contact with. They use microlithographic techniques borrowed from the semiconductor industry to carve the structures into solids. The sensors could possibly detect certain emissions at power plants or impurities in drinking water.

3 Light-Bouncing Bowls The bright-green color of the emerald swallowtail butterfly (Pap­ilio palinurus), found widely in Southeast Asia, is not produced by green light at all. The wing scales are covered with a grid of tiny, bowl-shaped dimples just a few microns across. The dimples are lined with layers of chitin separated by air, which act as selective mirrors. The bottoms of the bowls reflect only yellow light, and the sides of the bowls surrounding the yellow center reflect only blue. Our eyes cannot resolve the yellow and blue at such small scales, so our brain sees the combination as green.

Christopher Summers and Mohan Srin­i­vasarao of the Georgia Institute of Technology have copied this method for making color. To create the tiny bowls, they let water vapor condense as microscopic droplets on the surface of a polymer that is setting from liquid to solid. The water droplets pack together on the surface like rows of eggs in a carton, sinking into the film. The droplets evaporate as the polymer sets, creating a surface that has bowl-like dimples. The researchers then deposit thin, alternating layers of titanium oxide and aluminum oxide in each bowl to make a reflector that mimics the natural lining of the butterfly bowls.

Light bouncing off the patterned film appears green. When the film is placed under a set of polarizing filters, however, the yellow light bouncing back from the centers of the bowls disappears while the blue light from the rims remains. This mechanism could offer a distinctive authentication mark on credit cards and bank cards. What would appear as a simple green reflective coating would in fact carry a hidden, polarized yellow and blue signature that would be difficult to counterfeit. Srinivasarao admits, though, that the main reason they are trying to replicate the butterfly’s green color is that “it’s beautiful in its own right.”

4 Nanosponges Another butterfly, the emerald-patched cattleheart (Parides sesostris), creates green color by using a different nanostructure; again, no pigments are involved. Its wing scales sport microscopic, crystalline arrays of holes. These so-called photonic crystals totally exclude light within a particular band of wavelengths, causing that light to reflect. Opal gemstones are photonic crystals made from tiny spheres of stacked-together silica that scatter light, thus giving the stone its iridescent rainbow colors. Photonic crystals can be used to confine light within narrow channels, creating waveguides that could possibly steer light around the tight spaces on computer chips.

Under the electron microscope, the cattleheart butterfly’s wing scales display arrays with a zigzagging appearance—patches of sponge made from chitin with orderly patterns of holes that are around 150 na­no­met­ers or so across. Each patch is a photon­ic crystal set at a slightly different angle from its neighbors. The structure enables it to reflect light within the green part of the spectrum over a wide range of incident angles. Some weevils and other beetles also derive their iridescent color from photonic crystals made of chitin.

Biologist Richard Prum of Yale University and his colleagues have figured out how these photonic crystals grow as young butterfly wings develop. Essentially lipids in the embryonic wing-scale cells spontaneously form a patterned template in three dimensions, and chitin hardens around them. The lipids then break down as the cells die, leaving a hollow matrix with a regular pattern of voids.

Researchers are trying to make similar structures from scratch. For instance, lipidlike molecules called surfactants will form orderly sponges, as will so-called block copolymers. Ulrich Wiesner of Cornell University has used these copolymers to arrange nanoparticles of niobium and titanium oxide into mineral-like “nanosponge” structures.

These porous solids could find a wide range of applications, such as more efficient, low-cost solar cells. Moreover, Wiesner has calculated that nanosponges made from metals such as silver or aluminum could have the weird property of a negative index of refraction, meaning they would bend light “the wrong way.” Such materials, if they can be fabricated, could form superlenses for optical microscopes that can image objects smaller than the wavelength of light, which is not possible in conventional microscopes.

5 Crystal Fibers Animals can sculpt photonic crystals in many ways. The spines of some marine worms, such as Aphrodita (the sea mouse), contain hexagonal arrays of hollow fibers a few hundred nano­me­ters across. These arrays, made from chitin, exclude light in the red part of the spectrum, giving the Aphrodita spine an iridescent red color.

It is not clear if these optical properties have any biological function in the sea mouse. But applications in optical technology certainly exist for such light-manipulating fibers. Philip Russell, now at the Max Planck Institute for the Science of Light in Erlangen, Germany, has heated and drawn out bundles of glass capillaries into thin fibers laced with hexagonally packed holes. If a wider capillary or a solid rod is added into the middle of the original bundle, it creates a defect in the array of holes, along which light can pass while being excluded from the surrounding photonic crystal. This creates an optical fiber with a cladding that is essentially impermeable to light within a particular band of wavelengths.

Photonic crystal fibers “leak” less light than conventional ones, so they could replace the standard fibers in telecommunications networks. They would require less power, thereby eliminating the need for costly amplifiers to boost signals sent over long distances. Conventional fibers become particularly leaky at tight bends, where the reflections that confine the light inside the fiber are less efficient. Photonic crystals do not have this problem, because their light trapping does not rely on reflection. Thus, they should work better in small, confined spaces, resulting in optical microchips that are far faster than the electronic chips in our computers and cell phones.

6 Deformed Matrices To create colors, some creatures form spongy matrices that have a disorderly pattern instead of an orderly one. This structural variation creates the splendid blue and green plumage of many birds that lacks the iridescence seen on the hummingbird or the peacock. Because the spongelike keratin na­no­structures in these cases are disordered, the light scattering is diffuse, akin to the blue of the sky, rather than mirrorlike and iridescent, so the color appears uniform when viewed from any angle.

In the blue and yellow macaw (Ara ararauna) and the black-capped kingfisher (Halcyon pileata), the empty spaces in the matrix of the feather barbs form tortuous channels about 100 nanometers wide. A similar random network in the cuticle of the Cyphochilus beetle gives it a dazzlingly bright white shell. In the blue-crowned manakin (Lepidothrix coronata), the airholes are not channels but are little, connected bubbles.

Yale’s Prum thinks the channels or bubbles are created as keratin separates spontaneously, like oil from water, from the fluid in feather-forming cells during early development. He also thinks that birds have evolved a way to control the rate at which the keratin separates, so the channel or bubble formation stops when the voids reach a certain size. This size determines the wavelength of scattered light and thus the feather’s color.

Diffuse light scattering can be seen in other natural and man-made substances. In milk, microdroplets of fat with a wide size range scatter all visible wavelengths, thus creating an opaque whiteness.

Exeter’s Vukusic has mimicked the Cyphochilus beetle cuticle with random porous matrices of calcium carbonate or titanium dioxide mixed with a polymer, making thin coatings that are brilliantly white. Meanwhile Prum and bioengineer Eric Dufresne, also at Yale, have imitated the disordered sponges of bird feathers by creating films of randomly packed microscopic polymer beads, which have blue-green colors. These approaches could lead to coatings that have strong, highly opaque colors even though they are extremely thin, and the colors would never fade because the films do not contain organic pigments.

7 Reversible Proteins One of nature’s most enviable optical tricks is to produce reversible color changes. Squid in the Loliginidae family use a protein called reflectin to create and alter colors in their skin. The protein molecules are arranged into stacks of plates inside cells called iridophores, which reflect specific colors. Biologists think the color changes serve as camouflage and as communication for mating and displays of aggression.

Daniel Morse of the University of California, Santa Barbara, is studying how iridophores change color. The reflectin proteins crumple into nanoparticles, which form the plates. The plates are sandwiched between folds in the iridophore cell’s membrane. When a neurotransmitter activates a biochemical process that neutralizes the electrical charge of the reflectins, the proteins pack more closely. The change increases the reflectivity of the plates and changes their spacing, altering the color. The change can be reversed if the reflectins regain charge.

Morse thinks he can mimic this mechanism in optical devices, perhaps using reflectins themselves. His team has inserted the gene that encodes a reflectin protein in the longfin inshore squid Loligo pealeii into Escherichia coli bacteria. When expressed, the pro­tein collapses into na­no­particles. The par­t­icle size can be tuned with salts that control the interactions between charges on the proteins. The materials might then swell and contract, altering the reflected wavelengths in response to chemical triggers.

Morse has also developed a polymer that dramatically switches from transparent to opaque in response to electrical voltages, which alter the polymer’s reflectivity and swell the polymer film by drawing in salt. Devices using these materials can be made with simple, low-tech manufacturing methods. His team is working with Raytheon Vision Systems in Goleta, Calif., to turn this material into fast shutters for infrared cameras, thus enabling high-speed “night filming” by detecting heat rather than light. 

This article was published in print as “Nature’s Color Tricks.”