Removal of graffiti from quarry stone by high power diode laser

The integrity of architectural monuments in urban areas is threatened by numerous attacks, among which the graffiti is sometimes one of the most important. Particularly, Morelia's historic center (Mexico) (appointed World Heritage Site by UNESCO) suffers, for some years, a high number of graffiti. Most of these monuments in Morelia were built using a local stone called Pink Morelia Quarry. In this paper, we present the results of a study on the feasibility to remove the graffiti from Pink Morelia Quarry using a high power diode laser treatment. An extensive experimental analysis of the operating conditions has been carried out leading to successful results. The optimal parameters to achieve a total removal of graffiti have been determined. We concluded that continuous wave regime leads to better results than modulated wave regime, additionally, a two laser passes process demonstrated a high performance.

► Six colors of graffiti were removed from a building stone using a High Power Diode Laser. ► A new continuous wave multipass laser treatment provides the best results. ► An extensive analysis of the parameters in the process is reported. ► We obtained the optimal parameters to remove the graffiti without damaging the stone.