Laser cleaning of graffiti on stone

摘要

In present days graffiti is a common problem that many restorers have to deal with due to both its unaesthetic appearance and damaging nature for the surface beneath. We report laser cleaning of graffiti paints (black, white, blue, green and red) on limestone and granite. The efficiency of two laser systems is compared: high repetition rate (20 kHz) Copper Bromide Vapor Laser (CuBrVL) generating wavelength 510.6 nm and low repetition rate (up to 10 Hz) Q-switched Nd:YAG laser generating fundamental wavelength 1064 nm and its second harmonic 532 nm. The surface condition of the stone samples before and after cleaning is evaluated by means of optical microscopy. On that base, suitable working parameters are chosen in order to avoid under- or over-cleaning.