New Light Shed On Mystery of Maya Blue (VIDEO)

Researchers have made more progress in unraveling the enigma behind the iconic Maya Blue pigment used by the Mayans and other pre-Colombian Mesoamerican cultures in offerings, on palace walls, in pottery and murals and other contexts.

Maya Blue is characterized by its distinct blue color, but of scientific interest because the dye is highly resistant to chemical and biological deterioration.

It has been known that the unique azure pigment was made from organic and inorganic constituents including indigo dyes from the leaves of añil plants (Indigofera suffruticosa) and a natural clay with a crystalline structure called palygorskite. But how the ingredients were "cooked" and combined together to make the pigment has remained a mystery.

But researchers from University of Valencia and the Polythecnic University of Valencia (Spain) have come up with a new hypothesis about how it was prepared.

The dominant theory proposes that there is a single type of Maya Blue that was created by a specific bond between an organic dye from the añil plants and the inorganic palygorskite.

However the team of Spanish researchers rejects that "monoist" theory.

"We detected a second pigment in the samples, dehydroindigo, which must have formed through oxidation of the indigo when it underwent exposure to the heat that is required to prepare Maya Blue," stated Antonio Doménech, a University of Valencia researcher, in a statement. 

"Indigo is blue and dehydroindigo is yellow," the expert explained, "therefore the presence of both pigments in variable proportions would justify the more or less greenish tone of Maya Blue. It is possible that the Maya knew how to obtain the desired hue by varying the preparation temperature, for example heating the mixture for more or less time or adding more of less wood to the fire."

As there is no "recipe" for Maya Blue, the results of any study of the compound's creation are hypothetical.

However, Doménech and his team seem confident that the pigment was created in a two-stage process where the where water evaporates from the palygorskite and the indigo bonds to the clay, although a part oxidizes and forms dehydroindigo.

In the second stage it would appear that the dye disperses through the channels in the clay. "The process is similar to what happens when we pour a drop of ink into a glass of water," Doménech said, drawing a comparison, although he acknowledges that "this is a hypothesis" at present.

A video featuring the researchers discussing Maya Blue is here.