Comparative study on the application of the 1st and the 3rd harmonic of a Q-switched Nd:YAG laser system to clean black encrustation on marble

A comparative study on the removal of three different types of encrustation on marble has been carried out using infrared and ultraviolet nanosecond laser pulses. The fundamental and 3rd harmonic of a Q-switched Nd:YAG laser system have been used to remove dark dendritic, thin black compact and biological encrustation on marble. These three types of encrustation on Greek monuments have been previously described and relevant experimental work has been carried out. In the present work, samples from completion of Balanos restoration of Parthenon, from the Temple of Apollo Epicures as well as other regions have been used. It has been shown that both thin crust and biological deposits were adequately cleaned using the 3rd harmonic of the Nd: YAG system. The yellowing effect observed when using the 1064 nm pulses is definitely avoided in this case. However, the fundamental wavelength appears more efficient when dendritic thick black crust must be removed. To evaluate the results, X-ray diffraction (XRD) analysis has been carried out, while optical microscopy, cross-section analysis and scanning electron microscopy (SEM) were used to examine the irradiated areas and determine the cleaning efficiency of the two wavelengths applied. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.