Innovative conservation treatments for ancient silver objects

SiO2-like coatings have been deposited onto silver-based alloys by means of plasma-enhanced chemical vapor deposition (PECVD) fed with a tetraethoxysilane/oxygen mixture in order to study their capability to protect the alloys from tarnishing. Chemical and morphological characterization of the coatings has been carried out by means of X-ray photoelectron spectroscopy (XPS), infrared absorption spectroscopy, and scanning electron microscopy, while tarnishing susceptibility has been evaluated by means of visual inspection after intermittent immersions in Na2S solution at room temperature. It has been found that coatings deposited from oxygen-rich mixtures at high input power are characterized by excellent protective properties.