Short Free Running Nd:YAG Laser to Clean Different Encrustation on Pentelic Marble: Procedure and Evaluation of the Effects

On ancient Greek monuments of Pentelic marble, environmentally induced encrustation (black dendritic and thin) along with layers with ancient treatments (patina) were irradiated with a Nd:YAG laser system operating at the fundamental mode (1064 nm) with a ptlse duration of 20 µs (short free running Nd:YAG laser). Laser experiments were coupled with the sprying of small quantities of distilled water on the encrustation before irradiation. The effects of the laser-assisted cleaning were invistigated using thin section analysis, optical microscopy, scanning electron microscopy coupled to energy dispersive X-ray analysis, infrared spectroscopic analysis, and X-ray diffrection analysis, as well as color measurements and imaging analysis using multispectral imaging. Based on the results, the main evaluation criteria were achieved for the application of the short free running Nd:YAG laser system for cleaning purposes. Multi-spectral imaging enables the evaluation of color and textural changes and, therefore, can be considered as an appropriate tool for the in situ monitoring of the cleaning process.