Free-running Er:YAG laser cleaning of mural painting specimens treated with linseed oil, ''beverone'' and Paraloid B72

In this paper, preliminary results of laser-assisted (free-running Er:YAG laser) removal of several organic materials (i.e. linseed oil, ‘’beverone’’, Paraloid B72) applied to the surfaces of laboratory samples of mural paintings, are reported. The specimens were prepared with “a fresco” technique, using Saint John’s white and yellow ochre pigments. The optimal cleaning conditions were established between the ablation threshold of the surface treatments and the damage threshold of the pictorial layers. The laboratory samples were subjected to laser ablation in order to establish optimal cleaning conditions which were as regards for example linseed oil: 0.6-1.3 J/cm2, in the presence of isopropanol and an eventual chemical pre-treatment. These surfaces were characterized morphologically, by colorimetric measurements and microRaman spectroscopy, all measure-ments carried out before and after laser radiation. Laboratory experimentation provided useful information for cleaning tests performed in situ and on the ancient fragments of the mural paintings from the Camposanto Monumentale in Pisa.