Laser cleaning of archaeological bronze artefacts

The study is devoted to the development of tailored laser cleaning procedures for the selective removal of dangerous corrosion products on archaeological bronze artefacts, without affecting the metallic substrate. In order to optimise the cleaning methodology and assess the real feasibility of the laser treatments as conservation procedure for metallic works of art, a deeper knowledge of the laser-material interaction and an investigation of the effect of the different experimental parameters on the metallic surface are necessary. In this study, a set of artificially-patinated Cu-based reference samples were cleaned by using a near-IR Q-switched Yb:YAG fibre laser. Several laser parameters (e.g. pulse duration and output laser power) were considered. The artificial patinas and the cleaned samples were characterised from the chemical, microstructural and morphological point of view by means of X-Ray micro-diffraction, scanning electron microscopy and confocal microscopy in order to assess the effect of the laser parameters as a function of the composition of the patina. The preliminary experimental findings show that laser treatment is a powerful technique for cleaning ancient metallic artefacts; however, a careful selection of the laser parameters has to be performed in order to avoid any damage to the metallic surface. Further investigations are in progress to better understand the etching mechanism of the patina and to develop a non-invasive cleaning methodology.