Science and Archaeology in Painted Metaphors

10 MARCH 2009, PHILADELPHIA, PA—In earlier years this exhibition might have been only a display of interesting objects. Now, breakthroughs in our ability to read Maya hieroglyphs, new data from new archaeological discoveries, and new scientific techniques allow us to look at the artifacts in this exhibition from a fresh perspective. Scientific research leading up to and incorporated in to this exhibition include:

Looking for Chocolate: Residue Analysis
Dr. W. Jeffrey Hurst, Senior Food Scientist with Hershey Foods Corporation, conducted residue analysis on samples from the inside surface of a number of the pottery vessels in this exhibition in order to identify the almost invisible organic remains in some of them. Two of the vessels were found to have held theobromine and caffeine—two elements that occur together only in cacao seeds—suggesting that these pots at some point contained chocolate.

What does this tell us? With proof that chocolate was indeed present at Chama, Maya scholars can use other sources of information to surmise what this would mean to the region. Cacao was a trade item, a symbol of wealth, and an important ingredient in rituals, since it was believed to be one of the foods the gods bestowed on the Maya. The temperamental cacao tree (Theobroma cacao) will only bear fruit when grown no more than 20 degrees above or below the equator, in lands that receive at least 60 inches of rain annually, and where the temperatures do not dip below 60˚ Fahrenheit. That the tree could grow in Chama’s environment helped the site achieve greater importance than other villages along the Chixoy River. It was still grown at Chama as a valuable trade item into the 20th century.

Clues to Vessel Origins: Instrumental Neutron Activation Analysis

Dr. Ronald L. Bishop, Curator of Mexican and Central American Archaeology, together with M. James Blackman, Senior Research Chemist, and Erin L. Sears, Research Collaborator (all in the Department of Anthropology, National Museum of Natural History, Smithsonian Institution), took small samples (about 200-400 milligrams) from some of the ceramic objects in this exhibition in order to try to identify the clay source from which they were made.

The samples were subjected to a bombardment of neutrons in a nuclear reactor, transforming the nuclei of certain elements into unstable radioactive isotopes, which give off gamma rays of characteristic energy as they decay. These gamma rays are detected and counted, then compared with a reference material—including, in this case, natural clay from that same region, collected by curator Elin Danien during a trip to Chama—that has been treated in the same manner. In this way the concentration of several elements can be determined. This provides a chemical profile or “fingerprint” for the sample that, hopefully, when compared to the 30,566 samples in the Maya Ceramics Project database, will tell us the likely source of the clay from which a particular ceramic was made.

What does this tell us? The results from their analyses indicate that most, but not all, of the detailed polychrome vessels were manufactured in Chama—important information for the curator, reading the vessels’ storyline “headlines” as local news. Just as important, however, were results that indicate the various other ceramics of this site came from a wide variety of clay sources, clearly indicating extensive trade and exchange of these objects rather than a local origin.

Examination and CT Scans of the Human Record

Early in the 20th century, archaeologist Burkitt collected skeletal remains of 24 individuals from the site of Chama, and these specimens, primarily teeth and mandibles, were sent to the Penn Museum. In 1978, Dr. Janet Monge, then a first year graduate student working with Diane Chase and Stuart Eldridge, researched and reported on the collection. Now Acting Curator in charge of the Physical Anthropology section of the Penn Museum, she recently (2009) collaborated with the Radiology Department at the Hospital of the University of Pennsylvania to CT scan the collection, as part of an extensive CT project, funded by the National Science Foundation.

What does this tell us? Bones contain information about age of death, diet and disease. This collection has a story to tell. Many teeth were lost early in life from periodontal disease and cavities. The people of Chama seem to have suffered the effects of a primarily nutrient-poor carbohydrate diet of very soft foods, based on maize. Village life was tough and short – the average age at death of these people was probably 27 years of age.

Multispectral Imaging
Dr. Gene Ware, Brigham Young University, undertook multispectral imaging of a number of the pottery vessels in this exhibition during the conservation process in order to detect faint or missing designs. This method involves viewing these pots at different wavelengths within the electromagnetic spectrum from near ultraviolet through visible light to infrared.

What does this tell us? Different details become clear at each of the 11 different wavelengths recorded for each vessel, providing new and better information about the painted scenes. Because the carbon-based slip used to outline the figures is partially transparent to light at the longer wavelengths, we can pick up very fine details, including information that tells us how the artist worked—information that may help art historians to identify individual artists. In some cases, material identification becomes possible: with one vessel (object NA 10835), this technique helped explain an irregular brown line running down the vessel, as dark brown slip probably applied along a hairline crack on top of the painted scene, just before firing.

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