Laser Ablation of Silver Artifacts in Vacuum: Solution to Silver Tarnishing Problem

This work is a study of effect of laser ablation in different medium on silver artifacts. The effectiveness of laser ablation cleanness methods was evaluated in air, water and vacuum condition. The samples were subjected to HCl treatment for several hours to simulate the formation of chloride patina on marine archeological artifacts. Laser ablation removes the patina in all medium, reducing its thickness from 300 to few microns in air and water and eliminating completely the chlorine in vacuum conditions. However, it was observed the formation, during cleanness of a white patina in air and water and an increasing of oxygen amount on surface. This indicate that in ambient reach in oxygen laser ablation favorite the oxygen absorbance on surface and the formation of a thin layer of AgO which dulls the surface. This hypothesis is confirmed by the results of laser ablation in vacuum conditions where surface tarnishing was not observed. So, laser ablation in vacuum condition was indicated as the most effective procedure to clean silver artifacts.