Earliest Evidence of Indigo Dye Found at Ancient Peruvian Burial Site

The dyed fabrics represent the earliest known use of indigo in the world, predating Egyptian samples by about 1,600 years

This image shows a scrap of the indigo-dyed fabric (right) and a diagram of the cloth (left), highlighting the blue stripes. Splitstoser et al., Science Advances

Archaeologists recently uncovered several scraps of indigo-dyed fabric at the Huaca Prieta ceremonial mound in northern Peru. Believed to be about 6,200 years old, this find pushes back the date for the earliest known use of the dye by roughly 1,600 years, Cynthia Graber reports for Scientific American.

The small cotton scraps were discovered on a 2007 excavation of Huaca Prieta, found bundled and embedded in concrete-like layers on a ramp leading up to the temple. They remain in surprisingly good condition despite their age because of this unusual burial at the site.

"They were literally sealed under these new layers of building, but because the building material had so much ash in it, it leached into the textiles, making them a very dirty, sooty color," Jeffrey Splitstoser, archaeologist and textile expert at The George Washington University, told Stephanie Pappas for Live Science.

Though the fabrics’ color was initially hidden, when Splitstoser carefully washed the fabric, the true indigo color appeared. “It was at that point we realized that we probably had indigo, and that it was probably the world’s oldest indigo,” he told Graber. They published their findings this week in the journal Science Advances.

Prior to this discovery, the oldest known dyed fabrics were Egyptian textiles with indigo-dyed bands from the Fifth Dynasty, roughly 2400 BC. The earliest known examples of indigo in the Americas, however, were a mere 2,500 years old.

Almost all blue dye in nature stems from an organic compound, known as indigoid, found in a variety of plant genera. The source of indigo at Huaca Prieta was most likely Indigofera, an indigo-producing plant native to the tropics of South America. Plants are not the only source of indigo, however—ancient Egyptians also extracted high-quality indigo from sea snails. Today, indigo is largely synthetically created and is primarily associated with the color in blue jeans.

Splitstoser and his colleagues identified the indigo in the fabric scraps using an advanced analytical technique known as high-performance liquid chromatography. Splitstoser confirmed indigo in five out of the eight fabric samples he tested. The lack of indigo in three of the samples could be due to age, where the indigo had either washed out over time or degraded, Splitstoser told Dani Cooper of ABC Science.

The findings also validate the contributions of early people in the Americas. “We in the West typically skip over the accomplishments of the ancient people of the western hemisphere ... but in this case, the cottons domesticated by the people of South America and Mesoamerica form the basis of the cottons we wear today,” he said.

"The people of the Americas were making scientific and technological contributions as early and in this case even earlier than people were in other parts of the world," Splitstoser told Pappas. "We always leave them out. I think this finding just shows that that's a mistake."

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