Surface manipulation techniques of Roman denarii

This work presents results of macro, micro, and nanoscale surface characterization for a set of Roman denarii, ranging from 136 BCE to 240 CE, using large-scale X-ray fluorescence (XRF) mapping, particle-induced X-ray emission (PIXE) spectroscopy, focused-ion-beam-assisted scanning electron microscopy (FIB-SEM) with energy dispersive spectroscopy (EDS). The combination of XRF and PIXE, with varying beam energies, allowed for visualization and quantification of individual elements as a function of the surface distribution. These results helped to select suitable areas for FIB-SEM-EDS analysis. The edges of selected coins were polished to image the inner composition and surface morphology of the coins using a backscattering electron (BSE) imaging method and EDS mapping. Nanosized lamellas extracted from the coins were investigated by transmission electron microscopy (TEM) as well. The combination of these methods enabled the surface, the subsurface, and volume composition of these coins to be probed to better understand their production methods, their surface treatment methods, and their corrosion. The results also provide evidence that a particular surface treatment method, amalgam silvering, had been used to make authentic Roman coins as early as the third century CE.