Fe(III) and Mn(II) EPR quantitation in glass fragments from the palaeo-Christian mosaic of St. Prosdocimus (Padova, NE Italy): archaeometric and colour correlations

Abstract In this work, we present the results of the quantitative determination of Fe and Mn in different oxidation states, inferring a colour to the glass used in a palaeo-Christian polychrome mosaic of St. Prosdocimus in the Basilica of St. Justine (Padova). The colour in the glass is determined by the amount of the ions of the elements in different oxidation states. More than 3000 loose tesserae of this mosaic, characterised by a full range of colours, are available, with different features of opacity. For a representative batch of tesserae with different colours, the determination of Mn(II), Mn(III), Fe(II) and Fe(III) was obtained by using a combination of Electron MicroProbe Analysis (EMPA) and Electron Paramagnetic Resonance (EPR). A meaningful relationship between colour, and the ions content in the ancient glasses was found.