When Identity Sits on the Surface An Investigation into the Effectiveness of Surface pXRF for the Identification of Constantinian Copies in Romano-British Coin Hoards Volume I

The visual identification of contemporary copies (unofficially minted coinage) of the house of Constantine dated AD330-341 in hoards is difficult. This is in part due to the high production quality of many of the irregular coins, coupled with factors such as poor preservation, which makes distinguishing between if a coin is regular (officially minted) or irregular (unofficially minted) a challenge. While previous studies have identified X-ray fluorescence (XRF) as a potential way to identify irregular Constantinian coinage from hoards due to differing chemical compositions, there is lack of research into the suitability of the method on hoards from a range of diverse environments and it was unclear whether the depositional environment may negatively impact the success of the XRF method for the identification of irregular coinage. The primary aim of this thesis research is to determine the effectiveness of using compositional surface analyses with portable X-ray fluorescence (pXRF) paired with a statistical method as an identification method for contemporary copies. To achieve this a pXRF analyser was calibrated and a method was further developed, taking into consideration the potential of post-deposition modification of the composition by varying environmental factors. Six hoards from acidic, basic, and neutral environments (two hoards per environment, n=1,144 coins) were analysed and classified as regular or irregular based on their composition. These groups were then validated using Linear Discriminant Analysis (LDA) and a small subset of coins had drill samples taken and analysed with microwave plasma atomic emission spectroscopy (MPAES). This study is the first to assess the impact of the environment on the success of pXRF identification of irregular coinage; the key finding is that when properly calibrated pXRF can reliably identify irregular coinage with high accuracy in hoards from a range of environments and so identify more coins than using visual identification alone. The depositional environment was also found to have an impact on how coins were analysed with clear environmental surface patterns identified. This work also found an additional 171 previously unidentified irregular coins within the six hoards. It is concluded that the method is effective and reliable and that with properly calibrated equipment, surface readings in the corrosion surface layers can be used not only to identify irregular coinage but also to observe patterns within the copies and hoards and track the environmental impact on the hoards through their corrosion layers.