Maya Blue is the name of a hybrid organic and inorganic pigment, used by the Maya civilization to decorate pots, sculpture, codices and panels. While its date of invention is somewhat controversial, the pigment was predominantly used within the Classic period beginning about AD 500. The distinctive blue color, as seen in the murals at Bonampak in the photo, was created using a combination of materials, including indigo and palygorskite (called sak lu'um or 'white earth' in the Yucatec Maya language).
Mural at Bonampak, Chiapas, Mexico.
Maya blue was used primarily in ritual contexts, pottery, offerings, copal incense balls and murals. By itself, palygorskite was used for medicinal properties and as an additive for ceramic tempers, in addition to its use in the creation of Maya blue.
The striking turquoise color of Maya Blue is quite tenacious as such things go, with visible colors left on stone stele after hundreds of years in the subtropical climate at sites such as Chichén Itzá and Cacaxtla. Mines for the palygorskite component of Maya Blue are known at Ticul, Yo'Sah Bab, Sacalum, and Chapab, all in the Yucatán peninsula of Mexico.
Maya Blue requires the combination of ingredients--the indigo plant and palygorskite ore--at temperatures between 150 and 200 degrees centigrade. Such heat is necessary to get molecules of indigo incorporated into the white palygorskite clay. The process of embedding (intercalcating) indigo into the clay makes the color stable, even under exposure to harsh climate, alkali, nitric acid and organic solvents. The application of heat to the mixture may have been completed in a kiln built for that purpose--kilns are mentioned in early Spanish chronicles of the Maya. Arnold et al. (in Antiquity below) suggest that Maya Blue may also have been made as a by-product of burning copal incense at ritual ceremonies.
Using a series of analytical techniques, scholars have identified the content of various Maya samples. Maya Blue is generally believed to have been used first during the Classic period. Recent research at Calakmul supports suggestions that Maya Blue began to be used when the Maya began painting internal murals on temples during the late pre-classic period, ~300 BC-AD 300. However, murals at Acanceh, Tikal, Uaxactun, Nakbe, Calakmul and other pre-classic sites don't seem to have included Maya Blue in their palettes.
A recent study of the interior polychrome murals at Calakmul (Vázquez de Ágredos Pascual 2011) conclusively identified a blue painted and modelled substructure dated to ~150 AD; this is the earliest example of Maya Blue to date.
Maya blue was first identified by Harvard archaeologist R. E. Merwin at Chichén Itzá in the 1930s. Much work on Maya Blue has been completed by Dean Arnold, who over his 40+ year investigation has combined ethnography, archaeology, and materials science in his studies. A number of non-archaeological material studies of the mixture and chemical makeup of Maya blue have been published over the past decade.
A preliminary study on sourcing palygorskite using trace element analysis has been undertaken. A few mines have been identified in the Yucatán and elsewhere; and tiny samples have been taken from the mines as well as paint samples from ceramics and murals of known provenience. Neutron activation analysis (INAA) and laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) have both been used in an attempt to identify the trace minerals within the samples, reported in a 2007 article in Latin American Antiquity listed below.
Although there were some problems with correlating the two methodologies, the pilot study identified trace amounts of rubidium, manganese and nickel in the various sources which may prove useful in identifying the sources of the pigment. Additional research by the team reported in 2012 (Arnold et al. 2012) hinged on the presence of palygorskite, and that mineral was identified in several ancient samples as having the same chemical make up a modern mines at Sacalum and possibly Yo Sak Kab. Chromatographic analysis of the indigo dye was securely identified within a Maya blue mixture from a pottery censer excavated from Tlatelolco in Mexico, and reported in 2012. Sanz and colleagues found that blue coloration used on a 16th century codex attributed to Bernardino Sahagún was also identified as following a classic Maya recipe.
Recent investigations have also centered on the composition of Maya Blue, indicating that perhaps making Maya Blue was a ritual part of sacrifice at Chichén Itzá.
Thompson recovered one hundred human skeletons and hundreds of objects sacrificed by the Maya between about AD 500 and the Spanish conquest. Many of the objects recovered by Thompson are currently curated in Chicago's Field Museum, where they recently provided Wheaton College archaeologist Dean Arnold and coauthors with new information about the tenacious turquoise pigment known as Maya Blue. The report appears in the March 2008 issue of Antiquity.
Maya Blue, like other ancient manufactured pigments (such as Egyptian Blue and Chinese Purple) is quite stable, maintaining its bright turquoise color after hundreds of years and despite exposure to harsh climatic conditions. The sacred cenote at Chichén Itzá is a natural well into which humans and jade, wood, rubber and leather objects were thrown as sacrifices. Before these objects were thrown into the cenote, according to historical accounts, the Maya heated some of the objects and painted many of them blue.
Studies of Maya Blue in the 1960s revealed that the pigment was made of a combination of palygorskite and a tiny bit of indigo (about .5 to 1%). Palygorskite is a white clay called sak lu'um in the Maya language, and it was used for medicinal purposes and pottery temper. Indigo (the source of the blue color) is a plant (Indigofera spp); it was called ch'ooh in the Maya language and was also used for medicinal purposes. Researchers soon discovered that simply combining the two elements, however, did not produce a stable pigment. Only if the combination was exposed to sustained low-heat temperatures, about 150 degrees centigrade, would classic Maya Blue be obtained.
Some of the artifacts recovered from Thompson's 1904 dredgings are curated today in Chicago's Field Museum. Among the artifacts is a decorated tripod Mayapan bowl made between about AD 1300-1460. Dean Arnold was perusing the Thompson collection at the Field Museum when he noted a label "Blue on copal in bowl." Energy dispersive x-ray analysis of the material in the bowl revealed a combination of copal, palygorskite and indigo, suggesting to Arnold that the bowl had been used in an attempt to produce Maya Blue.
Copal (called pom) is a form of hardened resin from the sap of the copal tree (Protium copal), and it is basically a young form of amber. Copal melts at a temperature of about 150 degrees centigrade; it burns slowly and consistently with a pungent smoke. It had a widely documented role as incense in ceremonies throughout the cultures of Middle America.
The presence of partially burned copal, indigo and palygorskite within this bowl in the Sacred Cenote, combined with historical documents from Spanish chroniclers such as Bishop Landa, indicates that the production of Maya Blue was part of the ritual of religious sacrifice. Objects to be sacrificed would have been heated, painted or dusted blue and then tossed into the murky green water with a ceremonial sizzle.
Although he didn't understand it at the time, Edward Thompson identified evidence of the association of Maya Blue with sacrificial practice, when he dredged the Sacred Cenote in 1904. In his field notes he indicated that a 14 foot thick layer of blue silt was found at the bottom of the cenote. Arnold and colleagues believe this represents the accumulated remains of Maya Blue washed from hundreds of sacrificial objects.