Maya Blue Mystery

Anthropologists believe they have solved the centuries-old mystery of how ancient Mayans of Mexico and Central America produced the remarkably durable pigment called Maya blue (Antiquity 2008, 82, 151). Ancient Mayans used Maya blue to decorate sculpture (shown), pottery, and murals. The pigment is composed of 0.5 to 2% indigo, a plant-derived pigment, chemically bonded to the clay mineral palygorskite and is resistant to chemical or environmental degradation. Previous experimental work demonstrated that Maya blue can be prepared by prolonged heating of indigo with palygorskite, but scientists weren't sure how the Mayans accomplished this. A research team led by Dean E. Arnold of Wheaton College, in Illinois, and Patrick Ryan Williams and Gary M. Feinman of Chicago's Field Museum used scanning electron microscopy and energy dispersive X-ray spectroscopy to analyze a preserved sample of copal, a tree resin used as incense, with blue residue. The researchers found indigo and palygorskite had been mixed with the copal, leading them to conclude that ancient Mayans prepared Maya blue by heating a mixture of the three components over a low fire or by burning incense in the presence of a mixture of palygorskite and indigo.