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.
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.
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!