Evaluation of the effectiveness of laser crust removal on granites by means of hyperspectral imaging techniques

• Published in: Applied surface science Vol. 347; pp. 832 - 838
• Main Authors: Pozo-Antonio, J.S., Fiorucci, M.P., Ramil, A., López, A.J., Rivas, T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 30-08-2015
• Subjects: Biogenic patina; Cleaning; Crusts; Fourier transforms; Granite; Hyperspectral imaging; Hyperspectral imaging technique; Laser cleaning; Lasers; Patina; Sulphated black crust; Texture; Sulphated black crust; Biogenic patina; Hyperspectral imaging technique; Laser cleaning; Granite
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2015.04.182

•Hyperspectral imaging techniques for determining the degree of crust removal on granites used in Cultural Heritage.•Hyperspectral imaging techniques allow to in situ evaluate of the effectiveness of the laser cleaning.•Hyperspectral imaging data are consistent with the information obtained by conventional techniques about the cleaning effectiveness.
In this paper, we present a study of the application of the hyperspectral imaging technique in order to non-destructively evaluate the laser cleaning of the biogenic patina and the sulphated black crust developed on a fine-grained granite used in the construction of Cultural Heritage in NW Spain. The grained polymineral texture of the granite hinders the adjustment of laser irradiation parameters during the cleaning, and therefore the in situ process control. The cleaning was performed with a nanosecond pulsed Nd:YVO4 laser at 355nm. A hyperspectral camera was used to in situ assess the effectiveness of cleaning by recording images of the rock surfaces before and during the laser treatment. Different analytical techniques were used to test the ability of the hyperspectral imaging technique to evaluate the cleaning process of the granite samples: optical microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM - EDX), Fourier transform infrared spectroscopy (FTIR) and spectrophotometer colour measurements. The results indicated that hyperspectral imaging technique is a reliable and more affordable technique to in situ evaluate the process of laser cleaning of the biogenic patina and the sulphated black crust in fine-grained granites.