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Maya Blue Paint Mystery Solved?

Friday, April 5, 2013

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Spanish researchers say they have unraveled clues to the mysterious and durable blue paint used by ancient Maya.

Known as “Maya Blue,” the formulation is highly resistant to chemical and biological deterioration, according to researchers from University of Valencia and the Polytechnic University of Valencia. The vibrant blue paint covered palace walls, codices, pottery and perhaps even bodies during sacrifices for centuries in Mesoamerica.

The ingredients of the paint have long been known: indigo, a plant dye used for denim; and palygorskite, a type of clay characterized by its crystal structure full of internal channels.

Study Uncovers Second Pigment

However, the “cooking” of the unfading ancient paint has baffled all who have studied the coating.

The researchers report that they have found traces of another pigment in the blue paint, which they say sheds light on how it was processed.

Maya Blue
Constantino Reyes / azulmaya.com

Scientists have discovered new clues into the Maya Blue formula.

“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,” Antonio Doménech, a UV researcher, said in a statement to Spain's Scientific Information and News Service.

“Indigo is blue, and dehydroindigo is yellow,” he said, “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 [or] less wood to the fire,” Doménech added.

The study, “Application of solid-state electrochemistry techniques to polyfunctional organic-inorganic hybrid materials: The Maya Blue problem” was reported in the journal Microporous and Mesoporous Materials.

Mixing Theory

Further in the report, the researchers also arrived at a theory on how the dye molecules are distributed in the clay’s crystal network.

Some scientists believe the indigo adheres to the exterior of the palygorskite’s structure with the “brick” shape, although it could also form a sort of “cover” on the entrance to the channels.

Maya Blue
SINC

The team continues to investigate the secrets of the unknown chemical bonds that bind the paint’s components together, which is key to the formula’s resilience.

The chemists say that the indigo dye penetrates into the channels instead.

They suggested that two stages occur when both components are heated to temperatures between 120 and 180 degrees Celsius. In the first and fastest of the two stages, water evaporates from the palygorskite and the indigo bonds to the clay, although a part oxidizes and forms dehydroindigo.

"The process is similar to what happens when we pour a drop of ink into a glass of water," Doménech said, although he acknowledges that "this is a hypothesis" at present.

The team says it continues to investigate the secret of the unknown chemical bonds that bind the paint’s components together, which is key to the formula’s resilience.

Previous Report Questioned

Doménech says that a report published by U.S. anthropologists in 2008 on a bowl found in the Sacred Cenote of Chichén Itzá erroneously led some media outlets to state that the mystery of Maya Blue had been solved.

"The bowl contained Maya Blue mixed with copal incense, so the simplified conclusion was that it was only prepared by warming incense," Doménech said.

The researcher also notes, however, that the composition and function of Maya Blue could have varied down through the centuries.

"Although quite a few samples would be required, it could be possible to establish the evolution in its properties and preparation throughout the Maya culture from approximately 150 B.C. to 800 A.D., in such a way that we could establish a chronology based on analyzing the pigment.

"This provides a far more 'flexible' view of this culture, breaking with that traditional monolithic view of inflexible ritualism."

   

Tagged categories: Coating chemistry; Coatings technology; Color; Pigments; Raw materials; Research

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