Inspired by art, physicists probe the science behind the dazzling colors of polarization

In the mid-1980s, Boston’s Museum of Science approached Austine Wood Comarow, an artist then living in Southern California, to create an original piece of art. It would hang in a wing that included a planetarium and exhibits focused on the science of light. The museum wanted something big and dazzling, and Comarow was a natural fit. From the late 1960s until her death in 2020, Comarow created what she called “Polage art,” vibrant installations that coax rich, metallic-seeming colors out of bright white light shining through ordinary materials like cellophane or certain types of clear tape.

Artist Austine Wood Comarow created Human Connections for the Museum of Science, Boston. Thirty-eight hexagonal light boxes, each 5 feet across, aim to tell the history of communication among humans, starting with cave art. The sculpture’s kaleidoscopes only emerge when viewed through polarized lenses, which are suspended in an array in front of the piece. Image credit: Austine Wood Comarow (artist).

Comarow’s kaleidoscopes in the sculpture, which is called Human Connections, only emerge when viewed through a polarized lens. The museum piece, still on display today after more than 30 years, consists of a sprawling grid of 38 hexagonal light boxes, each 5 feet across, with an array of round polarized lenses suspended in front. The lenses reveal images hidden in the work. The space also contains rotating polarizers, through which viewers can see the entire image morph in form and color.

Decades after Comarow began creating her signature backlit art, engineers harnessed the effect to build the LCDs found today in bright televisions and computer monitors. Structural biologists use it in polarized light microscopy to study the inner structure of materials. And increasingly, in recent years, it’s drawn the physicists, engineers, and materials scientists who work with crystals into artistic pursuits. The colorful possibilities inspire those with artistic sensibilities, intrigue those with some knowledge of optics—and fascinate those who gravitate to both.

Artist Vance Williams created this piece based on the structure of isoniazid, an antibiotic used to treat tuberculosis infection. Williams’ mother was diagnosed with tuberculosis in her youth and benefitted from isoniazid treatment in the 1950s. Image credit: Vance Williams (artist).

Special Effects

Physicists describe the phenomenon as “birefringence.” Light passing through birefringent materials travels at varying speeds. Polarizing filters, which limit the light passing through to certain spatial planes, make it possible to produce dazzling colors with birefringence. The effect was first reported in a 1669 treatise on crystals by Danish mathematician Erasmus Bartholin, who observed that images viewed through a crystal of Iceland spar, or calcium carbonate, were doubled. He also noted that rotating the crystal around an axis caused one image to move around the other—laying the groundwork for the idea that the angle of light plays a key role in the resulting visuals.

In the centuries since Bartholin’s discovery, scientists have learned that birefringence arises in materials with anisotropic structure, meaning that their molecules aren’t neatly ordered in symmetric patterns throughout the crystal. They have also found ways to grow crystals of compounds, such as caffeine and citric acid, that have this property—and they have observed birefringence in many kinds of ice crystals. Birefringent effects have been found in the cornea of the human eye, and some types of living cells exhibit birefringence just before they divide (1). And birefringence shows up in many minerals as well; geologists have long used it to study thin slices of minerals to better understand their molecular makeup.

Painting with Light

Comarow found her way to birefringence through science, though not directly. In her early works, the artist experimented with novel ways to convey light and color that went beyond paints and palettes. “This was the 1960s; you wanted to find something different,” says David Comarow, a retired patent lawyer and Austine’s widower. “She was working with all these materials, wanted to see what she could do with them.”

One day, her first husband, an astronomer, crumpled up a piece of cellophane, placed it between polarizing films, and showed her the kaleidoscopic shimmer. She was hooked. The phenomenon was well known to astronomers, who use filters made of similar materials to study narrow wavelength ranges of light from space. Comarow decided to apply it to artistic, light-based works.

More recently, the idea of using materials to produce vibrant colors piqued the interest of physicist Aaron Slepkov, at Trent University, Peterborough, Canada, who uses polarized light microscopy. During the early days of the COVID-19 pandemic, Slepkov, long an admirer of Comarow’s work, set out to lay down the rules that describe how, exactly, colors emerge when polarized light streams through materials like tape and cellophane.

“I’ve been interested in art my whole life,” Slepkov says, “but I don’t have talent.” Nevertheless, he knows how to captivate an audience. Slepkov made a splash in 2019 when he described, to the delight of millions of YouTubers, why microwaved grapes explode into juice and plasma (2).

“As a materials scientist, I’m always wondering, ‘how do things grow? How do they form?’”—Vance Williams

In the summer of 2020, when the pandemic shut down his lab, Slepkov saw Twitter posts about “painting without pigment”—that is, manipulating color with layers of translucent material, rather than using paint and brushes. He began to probe how polarization and ordinary household materials interact and how behaviors could offer new opportunities for artists.

“I was playing with all these different types of tape, trying to see what kinds of colors I could make,” he says. “They were all different. Why was there a difference?” He wanted to connect physical attributes to particular color patterns, and he started by going through detailed notes that Comarow had made in the early 1970s, describing the results of using various types of cellophane behind polarizers.

“She had developed a way of writing down what materials she was using, like which roll of cellophane, what thickness,” says Comarow’s daughter Cara Ginder, who worked as her mother’s assistant. “It was almost like scoring music,” David Comarow says. He says Austine also experimented with changing the polarization, connecting bright colors with the orientation of the filter.

As he unpacked the science behind art by Comarow and others, Slepkov has repeatedly called on what physicists have already learned. It results from a kind of double refraction: As incoming light passes through transparent materials like cellophane and tape, it splits into two separate rays. The refraction depends on both the angle of the incoming light and its polarization, or the orientation of the light waves. If the light is polarized in the same direction as the optical axis of the material—an orientation of the crystalline structure—then it is refracted as a single beam, as it would behave in a material without birefringence. If it’s not, then the single beam becomes two with perpendicular polarizations (and different speeds).

This knowledge has led to the experimental and artistic methods used most often today. The human eye and most cameras can’t detect polarized light or see the birefringent light show unaided; that requires polarizing filters. Almost every application—from Comarow’s light sculptures to Slepkov’s kitchen cellophane experiments to polarized light microscopy—depends on them. If the polarizing filter is rotated to change which light waves pass through, the colors also change—as can be seen in Comarow’s Human Connections sculpture.

Bringing out the Colors

In his experiments on tapes, cellophane, and even plastic cutlery of varying thickness, Slepkov methodically plotted the intensity and colors of light that passed through materials of varying thickness, and through multiple layers. Those measurements, combined with already-known equations describing retardance and polarization, helped him determine mathematical curves that could describe—and be used to predict—the emerging patterns. His explanations, he says, offer a mathematical response to the qualitative experiments Comarow was carrying out in the 1970s as she varied the type and thickness of materials to achieve specific colors and effects.

Slepkov’s experiments showed, for example, why layering materials washes out colors and why two people, standing next to each other at the exhibit at Boston’s Museum of Science, will perceive varying versions of Comarow’s art. He also began to suspect that the usual explanation—that the effect arises from interference—didn’t describe the physics of what was happening.

Birefringent materials that vary in thickness or structure produce patterns that evoke those found on soap bubbles or oil slicks. But they’re not the same: Those colors emerge from interference of light at interfaces where different materials meet. However, Slepkov couldn’t find a contribution for birefringent materials.

“I began to wonder,” he says, “why the hell are we still calling it ‘interference colors’?” When he laid out his argument on Twitter, he was met with fast, staunch opposition from other physicists, who insisted that the word “interference” was appropriate. However, Slepkov kept steering the online conversations back to his evidence, which showed that the birefringent phenomena had a different effect on light that didn’t require interference.

Slepkov published his findings last July in the American Journal of Physics (3). His paper isn’t the first to connect properties such as thickness, layering, and crystal choice to the colors they produce when illuminated. But, he says, it did help illuminate outstanding questions about birefringence.

Coaxing Crystals into Art

Slepkov says his research has deepened his own understanding of the works of others. “I have a better appreciation for some of this beautiful polarization imagery,” he says.

Those include images by Comarow, whose works range from small, desktop light sculptures to giant installations, such as ones at Disney’s EPCOT Center, a science education center in Korea, and her sprawling piece in the Boston museum.

Even though the science and art of birefringence lead to similar light shows, artists and scientists are driven by different impulses and priorities. “As a materials scientist, I’m always wondering, ‘how do things grow? How do they form?’” says Vance Williams, a chemist at Simon Fraser University, Burnaby, Canada. In recent years, he has been experimenting with tools and techniques for growing crystals that display mesmerizing color effects that occur when they’re positioned between polarizers. However, when he’s focused on artistic works, he makes choices that affect how the crystal looks. His experiments with growing crystals for art don’t always produce interesting visuals, he says, but the failures still push his work forward. His recent images, which he often posts on social media, “are more about the aesthetic,” he says.

Williams says he often finds himself engaged in methods that might seem counterintuitive to a scientist, such as using a quarter wave plate to change the polarization—a choice that wouldn’t affect the scientific investigation—or rotating the polarizing filter to reveal certain colors. “They won’t help me characterize the material,” he says. “But I suspect it might give me a cool image. And that’s an interesting feedback loop.”

“I’ve really followed a trajectory toward the artistic side,” Williams says. For inspiration, he looks at images of molecular crystals or heads into Simon Fraser’s storeroom of chemicals left from experiments and demonstrations; he calls it the “chemical morgue.” There, he’ll see what’s on the shelves—and what’s safe to use for his birefringence experiments. “And I think, ‘OK, can you create a story out of this?’” Then, he chooses chemicals with anisotropic crystal structures and tests them with polarizers to see if they’re also birefringent.

In the last few years, he’s produced big, bright, orange-and-blue prints of citric acid and caffeine crystals and others grown from hippuric acid, which is isolated from horse urine (4). That’s one of his favorites, partly because it produces a mesmerizing appearance from an unexpected source. “People like the scatological,” he says. “And it’s really cute. It almost looks like pencil crayon shavings.”

Perhaps his favorite piece to revisit is a multicolored image of the structure of isoniazid, an antibiotic used to treat tuberculosis infection. It looks like a cluster of jagged, prismatic spikes, reminiscent of the glimmer crystals in Superman’s Fortress of Solitude. Williams says his mother was diagnosed with tuberculosis in her youth and was one of the first people to benefit from isoniazid treatment in the 1950s.

As for Slepkov, he hopes that providing a physical explanation of the phenomenon could inspire other artists with an eye for science. “I have some hope that an artist who is scientifically literate would pick up on” the connections between physical properties and aesthetic results, he says. “And if the right person sees it at the right time, it could not only spark interest, but get through the hump of [physics] understanding early on. Then, you can see what they’ll do, artistically.”