The ancient Maya civilisation used a rare type of clay called "palygorskite" to produce Maya blue. Combining structural, morphological and geochemical methods, Spanish researchers have defined the features of palygorskite clay on the Yucatan Peninsula in Mexico. These findings will make it possible to ascertain the origin of the materials used to produce this pigment, which survives both time and chemical and environmental elements.
A Spanish research team has traced the route followed by the Maya to obtain palygorskite clay, one of the basic ingredients of Maya Blue. "Our main objective was to determine whether the Maya obtained this clay from one place in particular," co-author of the study Manuel Sánchez del Río, a physicist at the European Synchrotron Radiation Facility in Grenoble (France), told SINC.
The team, including Mercedes Suárez, from the Geology Department of the University of Salamanca and Emilia García Romero, from the Universidad Complutense in Madrid, analysed various samples of palygorskite clay on the Yucatan Peninsula to compare them to samples from other places. The results are available in the latest edition of Archaeometry.
Palygorskite clay has been used in Mesoamerica since ancient times. Numerous data suggest the Maya were aware of its properties and, what is more, this clay was closely related to socio-cultural aspects of the Mayan culture.
"Present day native communities on the Yucatan Peninsula are familiar with and use palygorskite clay for a variety of purposes, ranging from making candles on All Saints' Day and household and artistic pottery to remedies for mumps, stomach and pregnancy pains and dysentery," Sánchez del Río explained to SINC. Nowadays, modern pharmacology uses clays like palygorskite to produce anti-diarrhoea medicine, a remedy the Maya began to use more than a thousand years ago.
However, palygorskite was mostly used to make the Maya blue pigment, which is produced by mixing indigo, an organic dye obtained from the plant of the same name, with a base of palygorskite clay. The resulting compound is extraordinarily resistant to chemical and environmental elements.
The researchers found samples of high-purity palygorskite clay in several locations on the Yucatan Peninsula, in a 40 km radius of the well-known Maya archaeological site of Uxmal. Some of these locations are well documented, but others have been discovered for the first time during this expedition.
The fact that this clay was abundant among the samples collected confirms that the mineral is common on the peninsula.
Crystal-chemical analysis then enabled researchers to obtain the formula for the composition of Mayan palygorskite clay: (Si7.96Al0.07)O20 (Al1.59Fe3+0.20Mg2.25) (OH)2 (OH2)4Ca0.02Na0.02K0.04 4(H20).
These results will be useful for studying archaeological remains with Maya blue and to determine whether the palygorskite clay used in the pigment was taken from Uxmal or the surrounding area.
Maya Blue was invented between the 6th and the 8th Century and can be found in sculptures, fresco paintings, codices and pre-Columbian decorations across Mesoamerica, from the Gulf of Mexico to the Pacific Ocean. It was used during the colonial period to paint frescos in churches and convents. Maya blue was rediscovered in 1931 and scientists were baffled by the stability and persistence of this colour found on objects dating back to pre-Columbian times.
This thousand-year-old pigment, which has proven immune to the passage of time, erosion, biodegradation and modern solvents, is considered the forerunner of modern hybrid materials, compounds of organic and inorganic design with interesting properties for use in high technology.
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