Laser cleaning of contamination on sandstone surfaces in Yungang Grottoes

Laser cleaning is firstly used to remove the contaminations on the sandstone surfaces in Yungang Grottoes. A Q-switched Nd:YAG laser operated at 1064 nm with a pulse width of 10 ns is used to perform the experiments. Before experiments in Yungang Grottoes, the laboratory experiments on sandstone samples obtained from Shanxi province have been conducted. The laser induced damage thresholds of the uncontaminated sandstones and the laser cleaning thresholds of ink contaminated sandstones have been obtained in the laboratory. The difference between the cleaning effects of dry laser cleaning and steam laser cleaning has been compared. On the basis of the laboratory experimental data, the experiments in Yungang Grottoes have been conducted and the results indicate that laser cleaning is safe and effective for removal of graffiti ink and black smudges of smoke.