Investigation of the laser cleaning effect on Gotlandic sandstone by means of colorimetric and surface analysis

The laser cleaning of historical sandstone was investigated using air and also pure N2 for shielding of the laser interaction region. The yellowing measured in the colorimetric L*a*b* space was lower by more than 20% for samples cleaned in nitrogen. The effect was ascribed to the dirt combustion products on the surface due to ablation plume and confirmed by the surface inspection.