Laser cleaning in the conservation of lapidary objects

Laser cleaning is a novel technique in conservation procedures that has been recently employed in operative tests for the removal of alteration layers from the surface of stone artefacts, such as statues, architectural elements and decoration of various monuments and façades. This technique shows several potential benefits, such as fine, controlled and selective cleaning operations, that permit the effective removal of also chemically complex alteration layers and preserve the original patina on the stone surface. Here we discuss the mechanism of laser-induced cleaning of encrusted stones and we present a study regarding laser cleaning methods and analyses on various types of stone such as marble, limestone and sandstone from the Cappella di Piazza del Campo and Palazzo Pubblico in Siena, Italy. A laser system dedicated to this purpose has been developed and tested in practical cleaning tests.