Laser cleaning of stones: optimising the laser parameters and treatment methodology

摘要

Laser cleaning of stones has collected so far the largest number of experiences, employing mainly Nd:YAG laser systems. This class of lasers has been typically used in the two standard emission regimes of Q-switching (QS, short pulse, 5-10 ns) and Free Running (FR, long pulse, 0.2-1.0 ms). In our 6 years experience on laser cleaning in conservation, we have studied the interaction process of Nd:YAG laser radiation with various types of stones and surface alterations in order to optimise the laser emission parameters in terms of efficiency and safety of cleaning operations. To this aim we have carried out a critical study on the possible side-effects, which could endanger the result of the cleaning, as well as the future conservation of artworks. Beside the standard parameters which can be easily adjusted in most of the commercial laser devices, we have considered also the role of the pulse duration, which was varied between the time limits of QS and FR regimes by using laser prototypes suitably developed by us. Such laser systems have been tested in laboratory studies on al large variety of stones and alteration, and are presently applied in the restoration of high valuable statues and facades of historical buildings. Moreover , the definition of a correct methodology of laser cleaning applications in conservation is presently carried out in co-operation with important public conservation centres of Italy.