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Revealing the secrets of ancient materials

By Kelly Foss

A new technique co-developed by a researcher at Memorial University is allowing archeologists to quickly identify whether the origins of ancient material samples are natural or formed by human activity.

Working with a team researchers from Duke University and the Weizmann Institute of Science in Israel, Dr. Kristin Poduska says they have determined a simple diagnostic test using infrared spectroscopy can track the crystallinity changes in the material, which can then determine how that material was formed.

Their findings have recently been published in the journal Advanced Materials and written about in Nature magazine.

The first material to be tested was calcite – a mineral that can be found naturally in limestone or marine shells, but also through human activity such as ashes from fires or plaster in building materials.

“Lots of techniques could tell you the structure and composition of the material and identify it as calcite,” said Dr. Poduska, an associate professor in the Department of Physics and Physical Oceanography. “But even if you know its calcite, you can’t tell how it was made or where it came from.”

Dr. Stefano Curtarolo, associate professor of mechanical engineering and materials sciences and physics at Duke University says the key to determining the origin lies in figuring out how well the crystal structure is organized.
“Naturally occurring calcite crystals are tightly organized, while a material created by humans from calcite is usually far less organized,” he explained.

Traditional methods of determining the crystal structure of a material were time consuming and included the use of highly specialized equipment that was far from portable, which made them less than ideal for using on-site at archeological digs. The new method is easily portable and can provide instant results. As different molecular units absorb light differently, they yield distinct spectral peaks – well-ordered materials have sharp peaks and poorly ordered materials have wide peaks.

Last summer the researchers, who also include structural biologists Steve Weiner and Lia Addadi, nuclear physicist Elisabetta Boaretto, archaeology PhD student Lior Regev, and theoretical physicist Leeor Kronik, successfully tested the new diagnostic tool in the field at archeological sites in Israel. Dr. Poduska says her colleagues are now looking into applying this method to teeth and bones. She is also hoping to test the tool on archeological sites in Newfoundland.

“Here there’s not a lot of call for plaster analysis, but I’ve been working with Dr. Pricilla Renouf (from the Faculty of Arts) to apply our analysis technique to other materials found at the Port au Choix National Historic Site. She has worked there for years because bones are quite well preserved there, unlike many other places in Newfoundland and Labrador. The Port au Choix area is different because it has a limestone underlayer, which we believe makes the pH of the soil less acidic so the bones survive longer.

“I’m currently working with her and her students to use these methods to identify places where there have been human fires. Heating limestone changes the chemical composition, and as it cools it reforms in slightly different ways, so the crystal structure changes.”

She currently has several undergraduate archeology students working with her in her lab testing the method on other heated materials including sediments and residues on artifacts.