The world's earliest known use of indigo dye has been traced to Peru. Scientists found evidence of the blue pigment being used around 6,000 years ago by a pre-Colombian civilisation.

Previously, the oldest-recorded use of such dyes had been in textiles produced in Ancient Egypt, some 4,400 years ago. First written mentions of indigo dye date back to 5,000 years ago in the Middle East. The new findings, published in the journal Science Advances, thus suggest that the Peruvian use of indigo dye predates the Egyptian use by about 1,500 years.

This discovery occurred in the context of excavation works between 2007 and 2009 by archaeologists Tom Dillehay and Duccio Bonavia at the site of Huaca Prieta, on the Peruvian coast. Numerous cotton textiles were found on the ramp leading to the top of the ancient mound temple - in layers of 'concrete' made from ashes, shells and sand.

Jeffrey C. Splitstoser from George Washington University, lead author of the paper, was invited during the last year of the project to examine the textiles.

"Pre-Colombian civilisations believed everything was alive and built and renovated temples over older pre-existing structures. Before new construction and renovation took place, they might have organised a termination ceremony for the old temple. It is possible that the textiles were deposited on the ramp leading up to the top of the temple as part of this termination ceremony", he told IBTimes UK.

Analysing the blue

The textiles had lost most of their colours, as they had been affected by ashes from materials being burnt at the temple, so at first Splitstoser did not notice the presence of blue dye. It was only in 2011, after the fabrics had been washed, that the colour was revealed.

Using sophisticated methods known as high-performance liquid chromatography and photodiode-array detection, a team led by Splitstoser and his colleagues Jan Wouters and Ana Claro, analysed a sample of blue yarn from one of the ancient blue-striped fabrics, along with samples of blue yarns from seven other fabrics from Huaca Prieta. In five samples of textile, they found out that the blue in the ancient cotton textiles came from plant-based indigo dye.

This makes the textiles the earliest-known evidence of indigo dye being used in the world, present in some of the most ancient cotton. The discovery highlights the important role played by ancient Pre-Colombian cultures in the development of the cotton industry.

"The fact that it is the oldest-known indigo alone, predating previous evidence of early use of indigo by 1,500 to 2,000 years is in itself significant. But also, this discovery shows the sophistication of the pre-Colombian civilisations when it came to manufacturing cotton and dyeing it. They were making scientific and technological contributions as early and in this case even earlier than other cultures. All too often these populations are overlooked, we never talk about their achievements in relation to our history. But the fact is, the cotton they were growing forms the basis of our cotton plants today", concludes Splitstoser.