People think the history of dying cotton blue with indigo in America is old, but actually, it’s ancient.

A new article in Science Advances details a discovery of indigo dyed fragments of cotton that were found inside the archeological site at Huaca Prietain, a large stone and earth ceremonial mound in northern Peru. Using liquid chromatography, the archaeologists were able identify the reminisce of indigo used to dye the cotton and estimate the fragments are at least 7,800 years old.

The discovery makes the cotton fragments the oldest example of indigo used by humans as dye. The previous oldest evidence of indigo use was from Fifth Dynasty Egypt in 4400 BCE, according to Scientific Advances. But as it turns out, it was not the Egyptians who first dyed cloth blue with indigo, now the record is held by ancient Peruvians in South America.

The indigo present in the cotton fragments was preserved because of the unusual circumstances of the site in the Andes. And like contemporary denim, the Peruvian fragments were woven with a warp and weft.

Jeffrey Splitstoser, co-author of the research paper said for National Geographic, describing the samples “You could see blue in some of the samples but they were mostly grey. You know how your blue jeans fade over time? Well, these were like 6,000-year-old blue jeans.”

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