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Effect of laser cleaning on Scottish granite

Initial results from studies of the effect of high power 1064 nm light from a Q-switched Nd:YAG laser on Scottish granites, commonly used in buildings and monuments, are described. Pink granites, were shown to undergo bleaching at energy densities close to those necessary for successful removal of black soiling. Element maps produced by energy dispersive x-ray analysis showed no change in stone composition before and after laser exposure. Further work is currently being carried out in order to obtain an understanding of the bleaching mechanism and damage thresholds, as it is necessary to determine damage thresholds for laser cleaning in order to protect vulnerable stone minerals.