Scientists clear up Maya blue mystery
Chicago anthropologists have solved the mystery of how the ancient Maya produced Maya blue, a vivid and virtually indestructible pigment that was used for painting religious objects and human sacrifices.
In the process, they have also explained the creation of a 14-foot-thick layer of blue sediment at the bottom of the Sacred Cenote, a deep well in the Yucatan Peninsula city of Chichen Itza into which more than 100 victims were thrown after their hearts had been cut out on a ritual altar.
The pigment, which mimics the brilliant Caribbean sky, was used on murals, pottery, rubber, wood and other items thrown into the well to placate the rain god Chaak and bring moisture to the region, which suffers a seasonal drought from January through mid-May.
Researchers have long known that Maya blue results from a strong chemical bond between indigo dye and palygorskite, an unusual clay mineral that, unlike other clay, has long interior channels. They have re-created the pigment by slowly heating a mixture of indigo and palygorskite, but it was not clear how the Maya made it.
The key was a three-footed pottery bowl that has been sitting in Chicago’s Field Museum for three-quarters of a century.
Anthropologist Dean E. Arnold of the museum and his colleagues reported Tuesday in the online edition of the journal Antiquity that the bowl contained copal incense and two other substances. Scanning electron microscopy showed that one of them was palygorskite.
Combining that with other evidence, they concluded that Maya blue was produced on-site during rituals by burning a mixture of copal incense, palygorskite and probably the leaves of the indigo plant. The pigment was then brushed onto sacrificial objects immediately before they were thrown into the cenote.
Although the pigment is long-lasting, it can be easily washed off painted objects unless special binders are used to set it. Hence, the blue sediment was the result of pigment washing off the large number of objects thrown into the cenote, Arnold said.
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