Investigation of surface laser treatment of ancient calcite: the case of the grave in Torricelle (Naples, Italy)

The laser-cleaning technique has been effectively employed in many areas. Recently it has led to a huge development in art restoration. However, this technique must be optimised to remove contaminations and encrustations from surfaces without generating any physical or chemical changes of the original material. Its use has been considered to clean a 4th century B.C. chamber gravesite in Torricelle, near Nola (Naples). The wall painting could not be seen owing to bioorganic surface layer and resinous material originated from surrounding pinewood. In order to evaluate the technique effectiveness we studied the interaction of the light from a Q-switched Nd: YAG equipped with SHG to work at wavelength of 532 nm. Several characterization techniques have been employed to verify the laser effect on the cleaning of the surface versus the operating parameter configuration and to evaluate the possible damages induced by the beam. In particular, micro X-Ray fluorescence (mu XRF) provided information on the chemical composition of the clean surface; X-ray microdiffraction (mu XRD) was used to identify the phases and their microstructures. These techniques were effective in assessing the quality of the cleaning process and for following the changes in the microstructure of the sample. Preliminary results suggest a possible influence of the laser on the aragonite-calcite transformation.