Enhancement of graffiti removal from heritage stone by combining laser ablation and application of a solvent mixture

In this study, it was evaluated the combined cleaning treatment based on laser ablation followed by the application of chemical products for removing alkyd graffiti paint from two different types of stone. Three different laser treatments (operated in Q-switched, long Q-switched and free short running modes) were applied to the stone samples. The best two treatments were then followed up by application of a chemical product (a low toxic ternary solvent mixture). The Q-switched and the long Q-switched laser treatments in combination with the chemical agent were more effective than either of the laser treatments alone, leaving fewer paint remains, but with minimal damage to the stone.