The dependency of ablation rate and wavelength is studied by means of an exemplary chosen sort of sandstone in order to determine the cleaning regime and the feasibility of different wavelengths for practical cleaning. Excimer laser radiation (KrF, XeCl) and Nd:YAG laser radiation (omega, 3 omega) were used for the ablation of the black crust and sandstone in two independent experiments with a constant number of pulses.