Renewing archaeological practice with modern technology: µXCT for the facile screening of excavated copper coins

Copper-based coinage represents a class of metal artefacts with extraordinary historical value. Although copper coins are frequently retrieved at excavation sites, they are typically found in a poor conservation state and are hardly identifiable. While the usual archaeological practice involves an approximate on-site cleaning process, this procedure remains rather controversial in view of its low efficacy and the risk of information loss [1]. Off-site cleaning is occasionally performed; however, the large number of recovered copper coins makes their study unsustainable in terms of time and human resources. This leads to entire coin collections being left unstudied [2]. Here, we highlight the use of lab-based X-Ray Computed Microtomography (μXCT) to address the above-mentioned limitations and demonstrate the feasibility of integrating this technique into the archaeological workflow. μXCT analysis has been performed on a group of Roman copper-based coins in their current state, as found during an archaeological survey. The reconstructed volumes have been elaborated to extract the key features required by numismatists for coins identification through database crosscheck. The same coins further underwent a physical cleaning performed by a professional restorer, to directly compare the traditional and the proposed methodology. The results prove the capability of μXCT in providing enough details to identify Roman copper coins. The comparison between the two methodologies shows that the XCT-based protocol outperforms the current practice on the coins reading (Fig.1), the mitigation of information-loss risk and time-consumption, setting a new paradigm for the study of large-scale collections of copper coins. In conclusion, we demonstrate that the integration of XCT into the archaeological practice is nowadays feasible and can significantly advance the work of archaeologists, numismatists, conservators and restorers.