Er:YAG Laser Applications on Marble and Limestone Sculptures with Polychrome and Patina Surfaces

The Er:YAG laser (2.94 µm) has been used safely and effectively to ablate contaminants from polychrome surfaces of marble and limestone sculptures. The pieces studied were 13th, 14th and 15th century polychromes and a patina surface of a Roman marble sculpture from the 2nd Century AD. The surface encrustations removed included calcite, gypsum, whewellite, soluble salts, atmospheric deposits, organic films, lichen and other fungal growths that cover the sculptures. The laser removal of organic deposits with the Er:YAG laser was especially effective. A microscopic study of the polychrome surfaces before and after removal of the encrustations showed preservation of the polychrome pigments. Infrared absorption and x-ray fluorescence spectral analyses of the ablated materials and of the surfaces before and after laser ablation were used for evaluation of the mechanism of the laser action and for comparison of the results of Er:YAG laser treatment with traditional conservation methods.