The cleaning of early glasses: investigation about the reactivity of different chemical treatments on the surface of ancient glasses

X-ray photoelectron spectroscopy (XPS) has been used to evaluate the reactivity of different chemical cleaning procedures on the surface of archaeological glasses. Investigations were performed on a series of Roman glass samples coming from Sicilian excavations. The ancient freshly fractured glass samples were subjected to different cleaning protocols such as piranha solution (solution of sulphuric acid and hydrogen peroxide) and EDTA/ammonia and citric acid/ammonia solutions at different pH values. The atomic concentrations of alkaline and alkaline-earth ions, measured using XPS spectra acquired at the surface of all the samples, revealed that, in acid solution, the reactivities of the EDTA and citric acid solutions were higher than that of the piranha solution. Moreover, in alkaline conditions, the reactivities of the chelating agent/ammonia solutions seem to be very high and effective in taking out alkaline and alkaline-earth ions and in destroying the external glassy structure with the formation of a silica gel thin film.