Studies on Alexandrian tetradrachms from the time of the Julio-Claudian dynasty
Following the acquisition of a portion of ancient pieces, including 627 Roman and Greek coins, from the Diniacopoulos collection of antiquities in 2001, the Queen’s Art Conservation Program and the Department of Classics recently prioritized the coin’s classification and authentication. So far, of the small number of coins verified, most have been identified to have been minted in Alexandria, Egypt. For such authentication purposes, a wide range of instrumental analytical techniques representing nondestructive, micro-destructive, and destructive techniques have been applied to the study of ancient coins and other artifacts. However, the techniques utilized for the aforementioned processes only yield elemental composition. Therefore, as the coins in question once belonged to the Diniacopoulos family who were also restorers of antiquities, identifying evidence of past restoration/conservation treatments including the presence of coatings is of high interest. Furthermore, it would be of high value to come up with an innovative technique that does not result in coin destruction.
Recently, University of Toronto researchers Dr. Rana Sodhi, Dr. Peter Brodersen (Department of Chemical Engineering and Applied Chemistry) and Research Technologist, Sal Boccia (Materials Science and Engineering) and affiliated with the Ontario Centre for the Characterization of Advanced Materials, had a collaboration with Queen’s University Professors: Amandina Anastassiades (Department of Art History & Art Conservation) and Cristiana Zaccagnino (Classics/Languages, Literatures & Cultures) assessed the viability of utilizing a combination of specialized surface analytical methods, namely, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) in conjunction with energy dispersive Xray analysis (EDX). They managed to obtain ample information results from the selected sample of ancient coins while minimizing the inevitable amount of damage, which would occur if destructive analysis was performed. Their work is currently published in Journal of Vacuum Science & Technology B..
The researchers commenced by selecting a specific coin which was of interest to them for further studies in relation to their previous work. Their studies started with large area imaging where ToF-SIMS was performed to map differences in surface composition. They then employed EDX mapping so as to gain more in-depth information. For the ToF-SIMS, delayed extraction had to be used, and in spite of challenging differences in topography, four areas were identified for further analysis.
The authors observed that ToF-SIMS allowed ease of locating the different areas by mapping differences in surface composition and providing depth information, while XPS allowed for more positive identification for the chemical species present and the relative composition. In addition, it was seen that a combination of ToF-SIMS, EDX, and XPS could provide much information and identify areas of interest for further analysis so that the amount of damage was minimized while at the same time maximizing on the information obtained.
In summary, the study by Dr. Rana Sodhi and colleagues presented and devised a protocol by which greatest amount possible of information could be obtained while minimizing the amount of damage that would inadvertently be incurred in such an analysis in rare and ancient artefacts. In general, results of depth profiles in the bulk of the chosen areas were presented in order to ascertain the distribution of the various chemical components for the coin used. Altogether, both ToF-SIMS and XPS have provided valuable information on the differences in chemistry and composition at the surface. This is a work-in-progress, with 2 further tetradrachms dated respectively to the time of Tiberius (14-37 AD) and Nero (54-68 AD) currently under investigation. To quote Dr. Sodhi, “We are very excited about applying modern surface analytical techniques to ancient artifacts as well as the cross-disciplinary nature of the work, and further, hope to apply this methodology to other items of cultural heritage.” He said in a statement to Advances in Engineering.
About the Collaboration
Ontario Centre for the Characterisation of Advanced Materials (OCCAM) is a unique facility providing enabling information for a wide array of applications covering the many disciplines involved with advanced materials. Located in the Departments of Chemical Engineering & Applied Chemistry and Materials Science & Engineering, University of Toronto, OCCAM has maintained its leading-edge capabilities after several successful CFI Leading Edge Fund applications. OCCAM actively caters to both academic and industrial needs by providing solutions to key problems as well as for research and development. Fostering collaboration between universities and industry, OCCAM allows for interactions that traverse the traditional boundaries between science, engineering, medicine and beyond.
In Spring 2017, Dr. Rana Sodhi (OCCAM), was approached by Prof. Cristiana Zaccagnino (Classics / Languages, Literatures and Cultures, Queen’s University) and Prof. Amandina Anastassiades (Art History and Art Conservation, Queen’s University) concerning the authenticity, manufacture and past restoration / conservation treatments of a set of 9 coins – billon tetradrachms, allegedly minted in Alexandria, Egypt and dating to Emperor Claudius (41-54 AD), which formed part of the Diniacopoulos collection of Central and Eastern Mediterranean antiquities at Queen’s University, and whether OCCAM could assist in answering these questions.
The cross-disciplinary nature of the proposed collaboration in combining modern surface analytical techniques to the study of ancient artifacts was of great interest to Dr. Sodhi and his colleagues at OCCAM – Peter Brodersen and Sal Boccia. They saw the opportunity to devise a protocol, utilizing a combination of Time-of-Flight Secondary Ion Mass Spectroscopy, X-ray Photoelectron Spectroscopy and Energy Dispersive X-ray analysis, by which the most information could be obtained while minimizing the amount of damage that would inadvertently be incurred in such an analysis. The work was presented at SIMS XXI (21st International Conference on Secondary Ion Mass Spectrometry) held in Kraków , Poland September 2017. This is a work-in-progress, with 2 further tetradrachms dated respectively to the time of Tiberius (14-37 AD) and Nero (54-68 AD) currently under investigation.
Prof. Cristianna Zaccagnino, Classics / Languages, Literatures and Cultures, Queen’s University
Rana N. S. Sodhi, Peter Brodersen, Sal Boccia, Amandina Anastassiades, Cristiana Zaccagnino. ToF-SIMS and other surface spectroscopies applied to the study of ancient artifacts Preliminary investigation of a tetradrachm of Claudius. Journal of Vacuum Science & Technology B, volume 36, 03F104 (2018)Go To Journal of Vacuum Science & Technology B