Degradation Products on Byzantine Glasses from Northern Tunisia

This study deals with the identification of the degradation products present on some Byzantine glasses coming from an archaeological excavation in Northern Tunisia. The main purpose of the present investigation is the identification of the products and the characterization of surface altered points, namely iridescent and black patinas, which are present on some selected glasses. Non-destructive techniques such as XPS (X-ray Photoelectron Spectroscopy), SEM-EDS (Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy), ATR-FTIR (Attenuated Total Reflection-Fourier Infrared Spectroscopy) and LA-ICP-MS (Laser-Ablation Inductively Coupled Plasma-Mass Spectrometry) are here exploited. SEM-EDS was employed to ascertain the morphological structure and the chemical composition of various points, apparently different, on the glass surfaces. Small area XPS was performed for identifying the elements present on the sample surface, for determining their chemical state and for establishing the atomic composition of the morphologically different regions. LA-ICP-MS was exploited to determine the chemical composition as far as the trace elements are concerned. The presence of iridescent patinas and of encrustations has been highlighted on the glass surfaces in correspondence to the altered areas: iridescent patinas are due to the fact that the glasses are depleted in alkali and alkaline earths. The incrustations resulted due to the presence of calcium carbonates, and/or oxyhydroxides. In one case sulfides were also detected by SEM.