The accidental hue

Throughout history, making a blue pigment has taken hard work—or a stroke of luck

CORVALLIS, OREGON—Mas Subramanian's most celebrated discovery came out of the blue.

As a solid state chemist at the chemical giant Dupont, Subramanian had put his name on hundreds of publications and dozens of patents. He identified a new superconductor and found a more environmentally friendly route to produce the chemical fluorobenzene. When he left the company to work at Oregon State University here in 2006, he set out to develop a multiferroic, a material with a combination of electronic and magnetic properties that could lead to faster computers.

Following one of Subramanian's ideas, graduate student Andrew Smith one day mixed indium oxide, manganese oxide, and yttrium oxide and heated the mixture in the oven. The resulting material, it turned out, didn't have any special magnetic or electric properties. It was just very blue.

Subramanian's first thought was that Smith, who had recently switched from marine biology to chemistry, had made a mistake. His second thought was something that someone at Dupont had once told him: Blue is really hard to make.

It's so hard, in fact, that Subramanian's new color became a phenomenon. The New York Times called within days after his paper on YInMn blue, as he dubbed it, appeared in the Journal of the American Chemical Society. Shepherd Color Company in Cheltenham, Australia, licensed the new pigment, which art historian Simon Schama has called "the bluest blue to date," and marketed it as a paint for artists. The new hue has inspired a music festival, and chip company AMD is using it to dye the housing of a series of graphics processors. "There is something about the color blue that just fascinates people," Subramanian says.

Humans made pigments from red and yellow ochre and charcoal at least 100,000 years ago, but they didn't have blue. The Babylonians and Egyptians used bits of lapis lazuli, a blue semiprecious stone, in statuary and art, but the laborious process needed to turn it into the pigment ultramarine was only discovered in the sixth century B.C.E. (Recent evidence from a burial site in Turkey suggests people also ground the blue mineral azurite down to a fine powder 9000 years ago, possibly for cosmetics.)

With natural blues scarce, people have tried to make their own. Ancient Egyptians mixed sand, plant ash, and copper to create Egyptian blue, the first synthetic pigment, about 5000 years ago. In the 19th century, chemists raced to create a synthetic ultramarine, and BASF spent an unprecedented 18 million gold marks, more than the company was worth at the time, to synthesize indigo, a deep blue dye from plants. These blues became some of the most sought after products of the booming chemical industry.

Yet blue pigments are still rare. Most blues in nature don't come from pigments that humans can co-opt. Animals such as the morpho butterfly and the blue jay appear blue not because of a pigment, but because their feathers or scales contain nanostructures that reflect light in a way that cancels out all but the blue wavelengths.

To appear blue, a dye or a pigment needs to absorb red light, which usually happens when red photons boost electrons in the pigment molecule from one energy level to the next. Because red light has the lowest energy of any visible light, those two energy levels need to be very close together—and such closely spaced energy rungs are found only in complicated molecules that are hard for organisms to make.

Plants have evolved many classes of pigments: Chlorophylls color leaves green; carotenoids come in orange (carrots), red (tomatoes), and yellow (maize); and betalains produce the red color of beetroot. But only one class of pigments is capable of producing blue: the anthocyanins. (The word literally means "blue flower.") And even most anthocyanins are not blue but red, because they naturally absorb blue light; only if the plant tacks on chemical groups can the molecule shift toward absorbing red.

In minerals, too, blue is a special case. Subramanian discovered that YInMn's color is created by a manganese ion surrounded by five oxygen atoms in a structure resembling two three-sided pyramids glued together at the bottom, a geometry rarely seen in natural minerals.

Designing materials from scratch to produce blue is difficult even today, Subramanian says. "So much chemistry has to come together," he says. Subtle changes in the arrangement of neighboring atoms can throw off the energy levels of an atom's electrons, altering the color it can absorb. The red of rubies and the green of emeralds both spring from chromium ions surrounded by six oxygen atoms; other atoms in the two stones cause the color difference by altering the chromium's energy levels. Such effects are very hard to predict, Subramanian says: "If rubies and emeralds did not exist in nature, no one would know how to create them."

But scientists have not given up hunting for new blues, continuing an age-old quest with 21st century tools. Although Subramanian's discovery came about by accident, other researchers are methodically using physics, chemistry, and genetics to find or create new blues for painters to dazzle with, edible colorants that make food more interesting, and blue flowers that, so far, only exist in artists' imaginations.