World’s most valuable dye existed in Peru 1,800 years before anywhere else

Ars Technica » Scientific Method 2016-09-18

Enlarge / A piece of 6,000-year-old yarn, woven into a sophisticated striped pattern. The blue stripes are dyed with Indigo blue, which doesn't appear elsewhere in the world for another 2,000 years. (credit: Science Advances)

One of the great technological breakthroughs in human civilization was textile manufacturing, which allowed people to weave and dye their own clothes from plants. Weaving was also fundamental for fishing, as it's crucial for making nets. And in the great empires of South America, weaving was also used to produce historical records. The Inca used a writing system called Quipu, where manuscripts were vast tapestries of carefully tied and colored knots, allowing them to produce records about everything from astronomy to trade. Now, a new study in Science Advances reveals that the people of South America were also the first to use indigo blue dye on their cotton fabrics. This dye, still in use today, is one of the most valued and popular in the world.

Archaeologists found evidence of indigo blue on cotton yarn found in Huaca Prieta, located in a lush seaside basin below the rocky mountains of northern Peru. It was once home to a bustling prehistoric settlement of farmers and fishers. People first came here 14,500 years ago, and within a few thousand years they had domesticated a number of staple foods such as beans and squash, as well as cotton. The ancient peoples of Huaca Prieta also left behind a ceremonial mound, full of valued goods and human remains. It was in this mound that researchers found several pieces of yarn, two dating back 6,200 years and 6,000 years. These items were subjected to a chemical and spectrographic analysis, and this showed conclusively the presence of two dye components, indirubin and indigotin, which are signature chemical compounds of indigo. It's unclear what plants the locals used to make indigo, but the researchers think it was likely Indigofera, which is native to the region.

We already knew that people first began domesticating cotton in this region 7,800 years ago, and now it appears that they were making elaborate, striped cloth with it less than 2,000 years later. Indigo was also used elsewhere in the ancient world, notably in Egypt and China, but the first known examples of indigo in the Old World are from Egypt, roughly 4400 years ago. Andean indigo was being used nearly two millennia before it was in Egypt.

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