Safeguarding history: U of T researchers team up with Royal Ontario Museum to preserve ancient Greek coins

Researchers are examining the chemical composition on the surfaces of ancient coins to advise museum conservators on how to treat and store them.

PhD candidates Maria Stanko (right) and Dian (Jack) Yu study images generated by energy-dispersive X-ray spectroscopy. Post-doctoral researcher Michel Haché looks on in the background (photo by Aaron Demeter)

Researchers at the University of Toronto's Open Centre for the Characterization of Advanced Materials (OCCAM) are working with the conservation team at the Royal Ontario Museum (ROM) to help preserve links to the past, ensuring important historical artifacts can be studied and shared with generations to come.

Maria Stanko, a PhD candidate in the department of materials science and engineering in the Faculty of Applied Sciences and Engineering, and her collaborators are studying the surfaces of two corroded Greek coins from the Hellenistic period – dating back to 300-115 BCE – using OCCAM’s instrumentation.

By understanding what is happening to these priceless relics, the team will be equipped to advise researchers and conservators on how to best conserve and store these artifacts safely.

The coins are subjects of study for the ROMkomma project, a collaboration funded by the Social Sciences and Humanities Research Council and led by Kate Cooper, an assistant professor, teaching stream in the department of historical and cultural studies at U of T Scarborough and research associate at the ROM, and Ben Akrigg, associate professor in the department of classics at the Faculty of Arts & Science.

The project aims to catalogue and publish data on the museum’s extensive collection of more than 2,000 ancient Greek coins. This investigation, which will make the ROM’s Greek coin collection accessible online, could reveal important insights on early minting practices and how early economies were developed.

Students and researchers from the department of materials science and engineering developed a plan to position and mount ancient Greek coins so they could be imaged and analyzed (photo by Aaron Demeter) 

“Environmental degradation is normal with coins that are thousands of years old,” says Stanko. “On a few of these coins, we’re likely seeing corrosion caused by elements like chlorine and bromine.

“These corrosive products are harder than the coin itself. We risk damaging the artifacts and removing the fine surface detailing if we try mechanical cleaning methods.”

The coin imaging and analysis project began as an assignment for the Analytical Electron Microscopy course Stanko took with Janet Howe, an associate professor in the department of materials science and engineering and the department of chemical engineering and applied chemistry and Stanko’s PhD co-supervisor.

Stanko and collaborators, including Howe, PhD candidate Dian (Jack) Yu and post-doctoral fellow Michel Haché, developed a strategy to examine the coins with a scanning electron microscope paired with energy-dispersive X-ray spectroscopy (SEM-EDS).

“Once we know more about the chemical composition on the surfaces of these coins, we can advise ROM conservators on non-destructive treatment strategies and storage solutions,” Stanko says.

The project has proven to be challenging. Since EDS works by exciting the electrons on the surface of a sample to emit X-ray signatures, the team needed to fix the position of the coins – without the use of clamps or guides that might cause damage – for the signals to hit the detector in just the right way.

One of the ancient Greek coins being analyzed at OCCAM is seen on the top left (photo: Laura Lipcsei, Royal Ontario Museum). The top-right photo shows a zoomed-in view of a section of the coin showing a corrosive product. SEM-EDS maps of the section of coin (bottom left and right) suggest the corrosion product is silver chloride (supplied image)

This type of analysis works best for smooth and flat objects, so the team spent hours examining the uneven faces of these coins under an optical microscope to identify specific areas where the samples could be imaged and analyzed.

Laura Lipcsei, a senior conservator at the ROM, says the museum is grateful to be able to work with OCCAM researchers. “We are so lucky to have this amazing resource available to us. It’s not just about having access to state-of-the-art technology and tools, this is an excellent team to work with,” says Lipcsei. “They are sharing important information, and we couldn’t do our work without them.”

The ROMkomma project is just one of many currently underway at the centre right now.

“OCCAM is the infrastructure supporting research across U of T and beyond,” says Howe, the newly appointed co-director of OCCAM, who played a leading role in installing the equipment at the centre.

“Many branches of science and engineering rely on understanding the structure of materials at atomic and nano scales, whether it’s related to designing catalysts for green energy, developing new biomolecules in medicine or enhancing microchips in our smartphones. Our work benefits every researcher tackling today’s grand challenges.”

Howe is looking forward to an upcoming collaboration with Hitachi High-Tech, involving a low-cost structural analysis tool that could significantly bring down the cost of characterizing the structure of new materials.

She identifies the centre’s focus on teaching as one of its core strengths.

“At OCCAM, we don’t restrict access to our world-class instrumentation to post-doctoral fellows and senior researchers. Undergraduate and graduate student get hands-on experience and are encouraged to come to us with projects.”