US researchers at Wheaton College in Illinois and the Field Museum in Chicago have unveiled the story behind Maya blue, a vivid pigment used widely for about a millennium by Mesoamericans. It was used to paint offerings, pottery, murals, and even the bodies of humans before ritual sacrifices.

"Unlike a lot of natural pigments that may fade, [Maya blue] is very stable," said Gary Feinman, curator of Mesoamerican anthropology at the Field Museum in Chicago, Illinois, per National Geographic.

All this was long known, but it was until now unclear how exactly it was made and used. The paper, which appears online today in the journal Antiquity, reveals that the pigment, which resists age, acid, weathering, biodegradation and modern chemical solvents, was made by mixing the ingredients over low heat in rituals performed on the edge of the sinkhole where sacrificial victims were thrown in.

The sacrifices were performed appealing to the Maya rain god Chaak to deliver rain for crops. "Adult males may have had their hearts removed before they were dumped in," Feinman said to Reuters.

"The offering of three healing elements (indigo, palygorskite, and copal) thus fed Chaak and symbolically brought him into the ritual in the form a bright blue color that hopefully would bring rainfall and allow the corn to grow again," said lead study author Dean Arnold of Wheaton College in Illinois.

The key to uncovering the actual preparation and use of the pigment, which is thought to have been discovered sometime around 500 A.D., was allegedly a small, three-legged ceramic bowl that has sat in the Field Museum for the last 75 years. Traces of residue found on the bowl and previous knowledge about Mayan rituals have yielded the formula and preparation technique.