LIBS tool to diagnose the Egyptian deteriorated wall paintings during laser cleaning process, an experimental study.

The wall painting surfaces represent the main challenge for the laser cleaning techniques. The objective of this work has been the study of the laser cleaning technique when applied to wall paintings. In particular, this study has been devoted to understanding how the characteristics of the laser apparatus and its specific use are linked with the nature of the substances to be removed from the painting. A number of artificially wall paintings were selected with paint layers that were composed of different pigments and covered with different dirties. In this work the feasibility of laser cleaning for the removal of dirties from the wall painting surfaces using Q-switch Nd:YAG laser operating at two different wavelengths: in the infra-red and in the visible (1064 and 532 nm) is presented. The effectiveness of the cleaning process was monitored by following the disappearance from the LIBS spectra of the deterioration aspects elements during successive laser shots. The aim of this work is focus on the definition of the experimental boundary conditions in which laser cleaning can be safely applied in cleaning of the deteriorated wall paintings.