National Geographic : 2003 Jun
THE SCIENCE OF THINGS Who Knew? CHEMISTRY We Got the Blues Humanity's obsession with a certaincolor When we finally get around to writing the entire story of civilization, we'll devote a chapter to the color blue. Sure, chil dren around the world choose red as their favorite color. But that's just a phase, like tearing the crust off bread. Make no mistake: Blue rules. For thousands of years humans have found ingenious ways to turn things blue. In the ancient Mediterra nean, biblical blue dye came from a hermaphroditic snail with a gland that generates a fluid that becomes blue when exposed to air and light at least when the mollusk is feeling masculine. "They had to extract the glands when the snails were more male than female," explains Tony Travis, a historian and chemist at Jerusalem's Hebrew University. Another blue dye came from a plant called woad. Its leaves had to be ground and fermented before the pigment emerged. Celts painted their bodies with it (think Mel Gibson in PHOTOILLUSTRATION BYCARYWOLINSKYANDDAVIDDERANIAN Braveheart). Medieval scribes illus trated manuscripts with it. The blue in woad came from a molecule scientists refer to as indigo. But woad wasn't the best source of blue. Another plant-also known as indigo-produced the color more effectively. Indigo plantations sprawled across Asia, while woad lost luster. Eventually synthetic dyes replaced natural ones. In 1897 the Germans manufactured the first synthetic indigo from coal-tar derivatives. Syn thetic dyes triggered an explosion of blue fashions in the 20th century. Policemen switched from black uniforms to blue. The blue blazer replaced the black suit. And in the 1950s blue jeans took off, radiating youth and rebellion. Next up: Biotech blue. When Aus tralian toxicologist Elizabeth Gillam was studying bacteria implanted with human DNA, her cultures unexpectedly turned blue. She suspected a mold contamination. But after conferring with Fred Guenge rich, a colleague at Vanderbilt University, Gillam realized she'd stumbled onto some thing wonderful: The bacteria were producing the indigo molecule as part of their metabolism. "This is a good lesson for student scientists," says Gillam. "If something looks bizarre, don't discount it. It might be much more interesting than the result you expected." Biotech indigo could be used to create blue plant tissues, including flower petals (imagine a perfectly blue rose). Scientists speculate that the process might even yield blue cotton, which would mean your jeans wouldn't need any dye. But then how would we ever get that nice faded look? -Joel Achenbach WASHINGTON POST STAFF WRITER Do blue jeans look more gray than blue to you? One in ten men and one in 200 women are born with inher ited color blindness. Difficulty distinguish ing shades of red and green is most common; trouble with blues and yel lows is more rare. But genes aren't the only cause. Some chemicals-solvents used in dry cleaning and in manufacturing products from power boats to rayon-can also damage color vision. University of Modena and Reggio Emilia professor Fabriziomaria Gobba says acquired color blindness matters because it's an early warning that toxins are building up in the body. His work, along with studies from China, Japan, and Turkey, suggests that officially "safe" exposure levels may be too high to protect the health of workers who aren't ready to settle for gray jeans. -Lynne Warren Learn more about making things blue-and find a link to Joel Achenbach's work at nationalgeographic.com/ ngm/resources/0306.