February 26, 2008
CHICAGO - The ancient pigment called Maya Blue - the color of a bright, cloudless Caribbean sky - has long fascinated scientists with its ritual uses and mystified them with its durable brilliance.
Victims chosen for human sacrifice were painted with Maya Blue from head to toe just before they were pushed to a stone altar to have their beating hearts cut from their chests.
The sacred pigment still decorates centuries-old temples and ceramic jugs, pots and jars, remaining unfaded and unchanged despite being long buried or long exposed to one of the world's hottest, wettest climates. Materials scientists figured out its components many years ago so they could reproduce it in modern times.
''But nobody had evidence of how the Mayans made this pigment, or where the manufacture of the pigment was done in ancient times,'' said Wheaton College anthropologist Dean Arnold.
In a paper published online Tuesday in the journal Antiquity, Arnold and his co-authors say they have found answers to those questions. The Maya, they believe, cooked up the pigment in ceramic bowls over burning incense near the sacrificial sites.
A key to the unlocking the mystery was a small, three-leg ceramic bowl that has sat in the Field Museum for the last 75 years, Arnold said.
The bowl was pulled from a deep pool known as the Sacred Cenote, a natural sinkhole at the magnificent Maya complex of Chichen Itza on Mexico's Yucatan Peninsula. The Mayas thought the almost perfectly round pool, nearly 200 feet across and more than 80 feet deep, was a portal to the spirit world.
Priests ritually flung sacrificial objects into its depths - ceramics, gold, humans.
A hundred years ago an amateur American archeologist, Edward H. Thompson, dredged the pool and sent thousands of objects to Harvard University's Peabody Museum, including 127 skeletons. The Peabody later traded some non-human objects with the Field Museum.
Arnold said he has worked off and on to solve the mysteries of Maya Blue since he wrote his dissertation on the paint's components for his 1967 master's degree at the University of Illinois. Several years ago he came across the Field's little bowl. It held a hardened mass of copal incense, a tree sap that gives off a sweet scent when burned.
Arnold noticed bits of white material in the copal that resembled one of the known ingredients of Maya Blue, a clay mineral called palygorskite. When he recalled that leaves of the indigo plant, another key component of the paint, was associated with priests' ritual burning of copal incense, the story began to come together.
''It began to look like the production of the ancient Maya Blue was based on the performance of the religious rituals,'' said Arnold. ''Healing was a sacred art in Maya culture, and palygorskite, indigo and copal incense all were thought to have healing properties.''
The Maya, who developed a written language as well as sophisticated mathematical and astronomical systems, built great cities with spectacular architecture and art in Yucatan. Their classic period ran from roughly 250 A.D. to 900 A.D.
The invention of Maya Blue around 500 A.D. is considered by some science historians to be one of the great technological marvels of antiquity, said Arnold.
Making it, he said, requires fusing palygorskite and a small amount of indigo over a slow, low-temperature source of heat, and he began to suspect that, for the ancients, the heat source was burning copal incense. It was a process that could be done in ceramic bowls at religious sacrificial sites like the Sacred Cenote.
To confirm his thinking he enlisted the co-authors of the paper: Jason Branden of Northwestern University's department of materials science and engineering, and Patrick Ryan Williams, Gary Feinman and J.P. Brown at the Field Museum's department of anthropology.
They used a scanning electron microscope to study the hardened incense, confirming the presence of palygorskite and indigo.
They also pulled together known historical and ethnographic records of Maya rituals performed at the Sacred Cenote, much of it from Maya artwork and documentation by Spanish colonizers.
Flinging blue objects and living humans painted blue into the pool was a way of placating the rain god Chaak, Arnold said. The rituals were performed in late winter, when the Yucatan turned brown for lack of rainfall and just before farmers planted their fields in corn.
The use of Maya Blue, he said, was ''symbolic of the healing power of water in an agricultural community.''
When Thompson dredged the Sacred Cenote, he found a 14-foot layer of blue silt at the bottom, said Gary Feinman, the Field's curator of Meso-American anthropology.
''He never asked why it was there, and nobody for decades ever seemed to think the blue silt was very significant,'' Feinman said. ''Now we have evidence that it came from Maya Blue made at the edge of the cenote during priestly rituals.''
Tough as the pigment is, Maya Blue needs time to dry and adhere to a surface. But the priests carrying out the rituals apparently painted sacrificial objects hurriedly before flinging them into the pool. The pigment washed off and sank to the bottom, Feinman said.
The team is now examining other objects from the Sacred Cenote in the Field collection for more information about the pigment, including what portions of the indigo plant the Maya used to produce it.
''This is a wonderful example of the value of great museum collections like the Field's,'' said Feinman. ''An artifact might sit here for a hundred years in storage, rarely looked at, and then prove to be vital in answering difficult research questions.''
Elizabeth Graham, a noted ceramic authority with the Institute of Archeology at University College London, called the research exciting.
''Maya Blue has been one of the big mysteries of archeology,'' she said. ''I think in archeology we tend to classify ceramics and their decoration, but we don't know how the heck (the ancients) made the stuff, where they got the minerals for colors, how they processed it,'' she said.
''Dean Arnold is probably the main person in the world today in the field of Maya ceramics and production, and he is confirming it here.''