FIB-FESEM and EMPA results on Antoninianus silver coins for manufacturing and corrosion processes

[EN] A set of ancient Antoninianus silver coins, dating back between 249 and 274¿A.D. and minted in Rome, Galliae, Orient and Ticinum, have been characterized. We use, for the first time, a combination of nano-invasive (focused ion beam-field emission scanning electron microscopy-X-ray microanalysis (FIB-FESEM-EDX), voltammetry of microparticles (VIMP)) and destructive techniques (scanning electron microscopy (SEM-EDX) and electron microprobe analysis (EMPA)) along with non-invasive, i.e., micro-Raman spectroscopy. The results revealed that, contrary to the extended belief, a complex Ag-Cu-Pb-Sn alloy was used. The use of alloys was common in the flourishing years of the Roman Empire. In the prosperous periods, Romans produced Ag-Cu alloys with relatively high silver content for the manufacture of both the external layers and inner nucleus of coins. This study also revealed that, although surface silvering processes were applied in different periods of crisis under the reign of Antoninii, even during crisis, Romans produced Antoninianus of high quality. Moreover, a first attempt to improve the silvering procedure using Hg-Ag amalgam has been identified.Financial support was provided by Sapienza University of Rome (Ateneo funding, 2014 15) and Spanish projects CTQ2014-53736-C3-1-P and CTQ2014-53736-C3-2-P, which are supported with Ministerio de Economía, Industria y Competitividad (MINECO) and Fondo Europeo de Desarrollo Regional (ERDF) funds, as well as project CTQ2017-85317-C2-1-P supported with funds from, MINECO, ERDF and Agencia Estatal de Investigación (AEI). PhD grants of the Department of Earth Sciences, Sapienza University of Rome, are gratefully acknowledgedDomenech Carbo, MT.; Di Turo, F.; Montoya, N.; Catalli, F.; Doménech Carbó, A.; De Vito, C. (2018). 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50 shades of colour: how thickness, iron redox and manganese/antimony contents influence perceived and intrinsic colour in Roman glass

Roman glass is studied here by means of optical absorption spectroscopy, in order to provide an objective method to quantitatively evaluate colour. The dataset is composed of 165 soda-lime silicate glass samples from various western European sites, mainly dated from the first to fourth century AD, and containing variable amounts of iron, manganese and/or antimony. Iron redox ratios and colour coordinates (based on the CIELab colour system) are determined and put in relation with the thickness of samples and their manganese/antimony contents. Results reveal thickness as a crucial parameter when discussing glass hues, thus leading to a differentiation between the \u2018intrinsic\u2019 and \u2018perceived\u2019 colour of glass objects (i.e. the colour of the object with the thickness normalised to 1\ua0mm, and that with its original thickness, respectively). Apart from HIMT and purple glass, the concentration of ferrous iron appears to be correlated with a*\ua0\u2014\ua0a colourimetric parameter determining how green the glass is. Significant relations of antimony/manganese contents versus iron redox and glass colour are also considered, resulting in quantitative arguments to entitle antimony-decoloured glass as the most oxidised and colourless glass