Laser Cleaning and Patina Depth Profiles of New and Ancient Copper Coins

This work presents and discusses a study of the oxidized patina on copper-based coins. Patina layers were characterized after thermal treatments on various coins and calibration samples using X-ray fluorescence (XRF) spectroscopy, which was employed to measure oxide layer thicknesses. Laser ablation of copper-based samples was carried out with an ns pulsed Nd:YAG laser operating at 1064 nm. The ablation yield was measured based on selected laser parameters and is analyzed in relation to controlled cleaning of different types of copper surfaces, either to remove superficial oxides from artistic or manufactured objects or to remove patina from old coins. As a micro-invasive technique, laser ablation may provide a methodological approach for patina thickness assessment and, in carefully controlled and case-specific situations, for selective surface treatment.