Laser cleaning methodologies for stone façades and monuments: laboratory analyses on lithotypes of Siena architecture

Abstract The present study was conceived for an evaluation of the effectiveness of laser cleaning techniques applied to samples collected from numerous monumental buildings in the city of Siena (Palazzo Pubblico, Cappella di Piazza, Baptistery, Logge del Papa and Palazzo Spannocchi). All the characteristic lithotypes of Sienese architecture are represented: Montagnola Senese marble, Cavernous limestone, Pliocene sandstone and Red Ammonitic limestone. The tests were devised so as to have the widest variability of situations in relation to the colour and composition of the lithotypes, the state of deterioration of the samples and the level at which to stop the cleaning. The tests were preceded and followed by detailed petrographic analyses. In the introduction to the work, we underline the importance of an accurate reconstruction of the stratigraphy of the external horizon of deterioration of the stone for an appropriate choice of the cleaning intervention; the potential advantages of laser techniques are consequently further emphasized.