Sci-Tech

The surprising science of blue jeans

A new video shows how jeans get blue, while new research from UC Berkeley shows how the dye used to get them that way could get greener.

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Indigo was once derived from plants before being widely replaced with synthetic dye. New research may bring it back to its roots and create more eco-friendly jeans. Video screenshot by Michael Franco/CNET

A new video from the American Chemical Society's "Reactions" series explains a lot about the pants that have clothed everyone from gold miners to hipsters over the past 140-odd years. For example, you'll discover how your jeans need to be treated in an alkaline bath to get the indigo dye to adhere to them and how they are yellow when they come out of this process until they come in contact with the air, which turns them blue.

One thing you might not discover from the video, however, is that a chemical in the indigo used to create all those jeans has been called environmentally damaging. As the video points out, indigo originally came from plants, but because of high demand, a synthetic solution was invented in 1897 by chemical company BASF. (BASF says the dye didn't start being sold for that purpose for another 17 years.)

According to a report this month from the University of California at Berkeley, the jeans industry now uses about 40,000 tons of indigo per year (the video says 50,000 tons of indigo dye are made each year, over 95 percent of it used by jeans manufacturers, which comes out to about 47,500 tons). But there are concerns that a chemical used in the production of indigo can be toxic to fish and some other aquatic life. "And when sent to waste water treatment plants, it severely corrodes the piping," the report says. Contacted by CNET about the claims, BASF said it stopped making synthetic indigo a few years back.

UC Berkeley bioengineering professor John Deuber (of the eponymous Deuber Lab) believes he may have a solution, says the report. He and his team decided to go back to the plant to see if there was a way to produce a "greener" indigo.

In indigo-producing plants, a chemical called indican is locked in the leaves within a cage made from a sugar molecule. Indican is a precursor to indigo and, in fact, when the leaves are mashed up, they turn blue because the indican is released.

Deuber and team discovered the enzyme responsible for creating the sugar cage and, by engineering bacteria with the enzyme's gene and other modifications, they believe they can turn the bacteria into indican-production machines.

Bacteria in fermentation tanks would churn out indican locked in sugar cages. A second enzyme would be used to remove the cage, initiate the final chemical reaction and deliver pure indigo dye without the need to use a petroleum-based process. This would lead to "greener" blue jeans.

"To find green solutions, our lab looks toward nature," Dueber says in the report. "We thought going back to the plants would be smart. If we can identify the enzyme the plants used to produce the sugar cage and clone its gene, we think the microbes can make large quantities of indican for dyeing jeans without the use of highly 'dirty chemicals.'"

Dueber is now working on perfecting the process and figuring out how to create and market a commercially viable product.