Nd, Er and excimer laser sources: laboratory evaluation of cleaning efficacy and of interaction with substrate

Three different laser sources (Nd:YAG, Er:YAG and XeCl Excimer) have been tested on two different stone materials important as concern historical use and diffusion as Carrara marble and Verona red limestone. Damage threshold and soiling removal efficacy have been evaluated using mycroscopical observations, chromatic measurements and weight loss. The obtained results encourage the research of alternative sources for stone cleaning with respect to the most used at the moment, namely Nd:YAG. In fact both Nd:YAG and Er:YAG lasers have provided good results even if delicate materials such as Verona red limestone must be cleaned with caution. As a matter of fact, Er:YAG source in particular represents an innovative cleaning method, even if needing further experimentation.