Abstract
Fiber optics reflectance spectroscopy (FORS) and visible and near-infrared (VNIR) hyperspectral imaging (HSI) were applied to assess and control the laser cleaning process of a deeply darkened limestone surface collected from the historic entrance gate of Castello Svevo, Bari, Italy. Both techniques enabled us to verify the different degree of removal of a thick deposit of black crust from the surface of the walls. Results obtained were in good agreement with those of previous studies of the elemental composition achieved by application of laser-induced breakdown spectroscopy (LIBS). Coupling FORS and VNIR-HSI provided important information on the optimal conditions to evaluate the conservation status and determine the more appropriate level of cleaning restoration, thus avoiding over- and/or under-cleaning. Imaging spectroscopy was used to obtain maps of areas featuring the same or different spectral characteristics, so to achieve a sufficient removal of unwanted layers, without modifying the surface underneath, and to increase the efficiency of traditional cleaning techniques. The performance of the combined non-invasive approach used in this work shows promise for further applications to other types of rocks and highlights the potential for in situ assessment of the laser cleaning process based on reflectance spectroscopy.
Highlights
In the past, limestones were one of the most widely used building materials for many monuments in the city of Bari and the Apulia region, Italy [1]
Limestone monuments often consist of overlapping rock layers that can be variously deteriorated, with formation of black crusts, solid concretions and corrosion layers induced by exposure to both weathering, which leads to their natural aging, and atmospheric pollution, which causes their degradation by dry and wet depositions [2,3]
The specific aim of this study was to test an innovative approach based on Vis–NIR–short-wave infrared (SWIR) reflectance spectrometry implemented as Fiber optics reflectance spectroscopy (FORS) and hyperspectral imaging (HSI) techniques associated with two multivariate algorithms, i.e., spectral angle mapper (SAM) and principal component analysis (PCA), for assessing and controlling the laser cleaning process and mapping layer surfaces of a deeply altered limestone fragment collected from this historical building
Summary
Limestones were one of the most widely used building materials for many monuments in the city of Bari and the Apulia region, Italy [1]. Limestone monuments often consist of overlapping rock layers that can be variously deteriorated, with formation of black crusts, solid concretions and corrosion layers induced by exposure to both weathering, which leads to their natural aging, and atmospheric pollution, which causes their degradation by dry and wet depositions [2,3]. These monuments require extensive and expensive and frequent cleaning works [3,4,5,6].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
