Archaeological breakthrough for Oriental Institute, Argonne

By William Harms
News Office

A team of scientists from the Oriental Institute and Argonne National Laboratory have utilized cutting-edge X-ray technology to perform chemical analysis of ancient artifacts, resulting in a more detailed chemical analysis of such objects than ever before possible.

The breakthrough came in an experiment conducted earlier this month at Argonne's Advanced Photon Source, where scientists passed a high-energy X-ray beam through a 5,000-year-old bronze figurine to determine its chemical composition.

"This is the most important scientific development in archaeology since the discovery of radiocarbon dating," said Aslihan Yener, Associate Professor in the Oriental Institute and head of the team that performed the experiment. Carbon-14 dating, which revolutionized archaeology, was developed at the University by Willard Libby, who won the Nobel Prize in 1960 for his work. It is the most widely used method of age estimation in the field of archaeology.

Using the APS to chemically analyze artifacts adds a new dimension to archaeological research. The experiment with the figurine, for example, revealed a higher concentration of tin in the bronze than archaeologists previously estimated, and it also showed that the artisans who produced the 11-inch figurine had a much higher level of technical skill than expected.

"I've been studying this artifact for years, but we've known relatively little concerning its chemical make-up," Yener said. "This technique allows us to determine the chemical make-up of metal artifacts in a way that adds a tremendous amount of new information about the metallurgy of ancient cultures." The discoveries came amidst a hum of excitement on the evening of April 1 as Yener, an expert on ancient uses of metal, oversaw a team gathered in one of the work areas that are part of the APS.

The APS, capable of producing the world's most brilliant X-ray beams, acts as a chemical microscope, recording such activities as the movements of atoms in an enzyme as it catalyzes a chemical reaction. Scientists from across the country use the APS for a range of biomolecular, chemical, environmental and materials research projects.

During the experiment, the bronze figurine, perhaps used in an ancient ritual, was placed on a tray in front of an X-ray insertion device, which looks similar to the instruments used in dental offices to focus X-rays on a patient's teeth. Outside the lead-encased X-ray room, a television monitor showed scientists where the ray was penetrating the artifact, while a spectrometer recorded the levels of chemicals on a computer screen. The team was able to scan the artifact as well as take precise readings at eight different points along its surface.

The statuette used in the experiment was recovered from an archaeological site at the border of Syria and Turkey near Antakya, ancient Antioch. The dig was conducted during the 1930s by Robert Braidwood, Professor Emeritus in the Oriental Institute, and his wife Linda Braidwood, Research Associate in the Oriental Institute. The Oriental Institute will begin to re-excavate these sites in August 1998 under the direction of Yener.

The artifact is part of a group of six figurines, three male and three female. The figurines, which fused together, had to be separated and cleaned of a green patina that had formed on their surface.

The cleaning may have removed some visible traces of metals. The advanced analysis performed at Argonne provided scientists an opportunity to determine if metals are present on the surface that would not otherwise be detectable.

"I'm interested in looking at the belt to see if there is any silver, which there was on the helmet, and other trace elements detectable on the torso," Yener said as she talked with scientists working on the spectrometer. As she spoke, a graph with peaks indicating which metals had been found appeared on the screen. In addition to silver, peaks on the chart revealed very high levels of tin, an element that was combined with copper to produce the bronze piece.

An intriguing portion of the object was a place near the feet, where the figurine had apparently been broken in antiquity and mended through soldering or brazing. The scientists aligned the beam with the break to determine the soldering materials, which turned out to include arsenic.

Yener theorized that the ancient craftsmen had used a form of bronze made from copper and arsenic to repair the figurine.

"The artists who created this must have been more advanced in their understanding than we thought, because they were able to determine that they needed to repair the object with metal that melted at a lower temperature than the original, otherwise they would end up melting the object itself," Yener said.

In the months ahead, Yener hopes to return to the APS to do further experiments with the artifact, including a cross-sectional high-energy image analysis (similar to a CAT scan), which will reveal more about how the piece was constructed.

In addition to Yener, other University team members include Laura D'Alessandro, Museum Conservator at the Oriental Institute; Joseph Smith, Louis Block Professor in Geophysical Sciences and Coordinator of Scientific Programs for the Consortium for Advanced Radiation Sources; and Elizabeth Friedman, a graduate student in Near Eastern Languages & Civilizations.