The Blue in Your Blue Jeans Traces Back to Peru, 6,200 Years Ago

September 15, 2016 | Erica Tennenhouse

Photo credit: Jeffrey C. Splitstoser et al., Science Advances (2016)

Peruvians were using indigo dye long before the Egyptians.

Archaeologists have discovered the oldest-known piece of fabric to be decorated with indigo — the same dye used today to give blue jeans their blue color.

The scraps of woven cotton were found at the Huaca Prieta site on the north coast of Peru.  Occupied between 14,500 and 4,000 years ago, this site has produced some of the earliest evidence of the use of cotton.

Only the faintest traces of blue pigment adorned some of the pieces of fabric, so the researchers performed chemical analysis to search for the telltale signs of indigo dye — the chemical compounds indigotin and indirubin.

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Of the eight tested samples of blue-ish fabric, the presence of indigo was confirmed in five.

Some of the samples were known date 6,200 years ago, making them the oldest examples of the use of indigo. Previously, the Egyptians were thought to have pioneered the use of indigo dyes, but it turns out they were 1,500 years behind the Peruvians.

As the George Washington University’s Jeffrey Splitstoser, lead author of the study published in Science Advancestells LiveScience, producing indigo dye is a complex process that involves fermenting leaves and aerating the resulting mixture to allow the solid compounds to separate from the liquid. The solids can be dried and stored, and reconstituted with an alkaline substance, which makes white indigo. Dipping fabric in white indigo causes it to turn yellow, then green, and finally blue, he explains.

Impressively, the study suggests that Peruvians had mastered this difficult process before anyone else.

“Some of the world's most significant technological achievements were developed first in the New World,” Splitstoser tells The Daily Mail. “Many people, however, remain mostly unaware of the important technological contributions made by Native Americans, perhaps because so many of these technologies were replaced by European systems during the conquest.”

“However, the fine fibers and sophisticated dyeing, spinning and weaving practices developed by ancient South Americans were quickly co-opted by Europeans,” he says.

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