Uncovering ancient forgeries in the Cornell Coin Collection

After a long hiatus due to the ongoing Coronavirus pandemic, the LOL pXRF (Portable X-Ray Fluorescence) spectrometer was once again called into action at Cornell’s Rare and Manuscript Collections Library (RMC). Cornell graduate students and researchers have utilized the CIAMS pXRF for a wide range of cultural heritage projects in the past, but this current project breaks new ground. 

Louisa Smieska (l, CHESS) and Olivia Graves (r, Classics) use the LOL pXRF to examine coins in Cornell’s RMC.

The Cornell Coin Collection contains about 1,500 Greek and Roman coins, but some of these coins might be ancient forgeries. Olivia Graves, a PhD student in Classical Archaeology, has conducted research on counterfeiting behavior in the ancient world and she recently noticed that some coins in the collection looked a bit “off.” Silver coins produced in the Mediterranean world from c. 400-50 BCE were almost purely silver and people typically counterfeited these coins by covering bronze or copper blanks in a thin plating of silver before stamping them and putting them in circulation. Upon closer inspection of photos in the collection’s online database, Olivia discovered that a few coins had flecks of green patina and orange rust on their surfaces – a clear sign that at least some coins in the collection are likely silver-plated counterfeits.

Roman Coins in the Cornell RMC

In order to test this theory, Olivia took the LOL pXRF to the RMC library along with Dr. Adam T. Smith, Director of CIAMS, and two post-doctoral researchers at the Cornell High Energy Sychrotron Source (CHESS), Dr. Louisa Smieska and Dr. Hazar Şeren. They tested 25 coins in their first preliminary visit; about half of these coins were suspected to be counterfeits and the other half were suspected to be real coins from similar time periods that could act as controls. These first tests provided some intriguing results. For example, two coins from a 2nd-century BCE mint from Athens were tested. The suspected-real coin gave results of over 98% silver on the surface. The suspected-counterfeit coin, on the other hand, turned out to be a metal cocktail: 80% silver with the remaining 20% made up largely of copper, tin, rhenium, and mercury! Yet another reason to wear gloves when handling artifacts.

These pXRF tests strongly suggest that the Cornell Coin Collection does indeed contain some ancient forgeries and Olivia hopes to conduct further tests in the coming months. Stay tuned!

LOL’s pXRF Get’s Up Close and Personal with a Rembrant

 

On Thursday, April 9, Dr. Jennifer Mass, senior scientist, Conservation Research Laboratory, Winterthur Museum, served as guest lecturer in the the Mellon-supported interdisciplinary seminar ARTH 4605/6605: Art|Science Intersections: More than Meets the Eye, offered jointly by Dr. Andrew Weislogel, Askin curator of Earlier European and American Art at the Johnson Museum and Professor Lisa Pincus of the History of Art and Visual Studies. Core Cornell presenters for the course have included Professor C. Richard Johnson of the School of Electrical and Computer Engineering, Dr. Arthur Woll of the IMG_1221Cornell High Energy Synchrotron Source (CHESS), and Professor Sturt Manning of CIAMS.

The loan of LOL’s handheld X-ray fluorescence spectrometer allowed Dr. Mass to demonstrate to students the process of distinguishing elements in historic pigments in the Museum’s School of Rembrandt Still Life with Dead Game painting, which had been the subject of prior investigations including x-ray fluorescence mapping at CHESS and microscopy of cross-section samples previously taken by Dr. Mass. In class the students were able to witness the XRF spectrometer detect mercury in the crest of one of the ducks’ heads, which indicates a bright vermilion red pigment that has since darkened to brown. The XRF device also detected cobalt, a key element in the 17th century pigment smalt, which is made from ground cobalt blue glass. This pigment also darkens to grey-brown over time. These real-time demonstrations were crucial for the students’ realization that the colors we see in historic paintings are often much different from what the original artists intended. Dr. Mass expertly guided the class in the demonstration, showing setup of the device and use of the software to distinguish between elements desired for the experiment and those of lesser interest that commonly occur.