Theoretical and experimental approach on laser cleaning of coins

Laser-based techniques are used more and more frequently for the cleaning of artifacts. Due to the different behavior of each material, when it is irradiated, studies and experiments are performed in order to find the optimum laser parameters for each case. In this work, the laser cleaning of coins is examined. Coins are studied with analytical methods in order to detect the corrosion products and the accretions. This information along with the composition of the coins' alloys is fed into an in-house developed program which estimates the penetration depth of the laser beam as well as the laser fluence for which the alloy starts to melt. Exploiting this information, laser cleaning of coins is performed with various conditions and parameters. Finally, the result is evaluated by using microscopic methods. From this research, it was found that the laser cleaning of copper, silver and aluminum alloys is feasible with Q-switched Nd:YAG at 1064 nm. Also, higher level of corrosion and accretions requires higher laser intensity. For low corrosion level on copper alloys, a thin water film on the irradiated area is beneficial.