Effectiveness and harmfulness evaluation of graffiti cleaning by mechanical, chemical and laser procedures on granite

Taking into account the graffiti extraction degree, it was found that blue, red and black colours were successfully extracted by all the evaluated methods. However, the extraction of silver colour, whose chemical composition differs from that of the other three colours, was more difficult and it was only achieved by the mechanical procedure and by several chemical products; Nd:YVO4 laser at 355 nm was an ineffective procedure in removing this paint. All the cleaning methods produced damage on the granites: a roughness increase after the mechanical cleaning, chemical contamination related to some chemical procedures and melting of biotite crystals after laser cleaning. Moreover, the ability of different paints to penetrate into the rock affected the global cleaning effectiveness evaluation.