Invited Paper CS-FrM3
Faces from the Past: Microbeam Imaging and Analysis of Artifacts from ancient Mesoamerica

Friday, November 14, 2014, 9:00 am, Room 313

Working in the analytical laboratories in the Department of Mineral Sciences in the National Museum of Natural History provides plenty of challenging problems just involving geologic materials. Requests from other departments within the museum and elsewhere are growing as the understanding spreads to other disciplines of how our tools can be applied to an even wider variety of materials. Here we provide details about two recent and ongoing studies of cultural artifacts from ancient Mesoamerica. These studies were performed using a variable pressure field emission FEI NovaNanoSEM 600 outfitted with a ThermoFisher silicon drift detector energy dispersive x-ray spectrographic (EDS) analysis system. They were conducted on uncoated whole specimens or fragments and tiny samples removed from the surface or from deep recesses of the objects.

A large collection of spectacular artifacts was delivered to the museum with a request to provide information as to their authenticity. The collection included carved stone figurines and masks and ceramic pieces with various surface coatings. The objects were photographed, measured and placed into groups based on their apparent cultural affinity. Initial observations were made using optical microscopy with particular attention paid to tool marks. In the SEM, some whole artifacts stretched the limits of sample chamber size and geometry. Very few objects showed evidence of modern tools at either the optical or SEM scale. Chemical compositions of minerals in, and surface coatings on, stone artifacts were determined in order to characterize the rock type and other materials. Rock types included jadeitite, serpentinite and syenite. One group of several syenite masks were partially coated with a probable modern tan gypsum plaster. Several ceramic artifacts of unique design have complex surface decorations. A small cross-sectional multi-colored fragment of the coating on one object was studied in detail revealing five chemically distinct layers. We interpret this as original Olmec fresco paint. The results of the ongoing research indicate that the large majority of the artifacts are authentic pre-Columbian objects belonging to the Olmec, Maya, Teotihuacan and Mezcala civilizations which date from 1500BC to 600AD.

In the first comprehensive study of the iconic stone “masks” from Teotihuacan (100 BC to 600AD), we examined nearly 200 masks. Sampling of the artifacts was prohibited however silicone molds taken austensibly to study tool marks and carving methods also removed tiny grains from deep in drill holes. Study of these grains reveal that some are very likely residue from the original carving and polishing of the stone.