The Laser Induced Fluorescence (LIF) technique has been already proved to be a powerful diagnostic tool for artworks. The aim of this work is to validate LIF measurements to detect the different detrimental effects of the environmental conditions on the stone materials and to discriminate among different biofilms and crust from smog or pollutants, in order to optimize the restorers’ interventions. A scanning LIF system at 266 nm excitation wavelength has been employed. The line scanning system has operated in two operating mode: reflectance and fluorescence. Reflectance measurements are made by performing a scan while the laser is off and the sample is exposed to the light emitted by a NIST traceable lamp. The result gives for each pixel of the scanned area the reflectance spectrum, from which the CIE/lab coordinates can be computed once the system is calibrated against a reference surface. The samples were placed on a holder for LIF measurements. The acquisition system was placed at than 3.5 m distance from the target and several images acquired with a spatial resolution of approximately 0.0025 m. The most relevant spectral features of crusts are identified by Principal Component analysis. Three groups of samples can be detected: a) samples with blue false color in the images, that are mainly formed by biocrust, b) samples mainly composed with crust and deposits with yellow or green colour, c) samples with no difference between faces. These classifications of samples are mainly according to the results obtained by morphometric techniques. LIF and reflectance measures seems a very powerful technique in this preliminary results, to discriminate the presence of biocrust and crusts/deposits with more sensitive that a naked-eye at 2.5 m of monuments. © 2014 Taylor & Francis Group, London.
Laser induced fluorescence applied to diagnosis in calcareous stones
Fantoni, R.;Colao, F.
2014-01-01
Abstract
The Laser Induced Fluorescence (LIF) technique has been already proved to be a powerful diagnostic tool for artworks. The aim of this work is to validate LIF measurements to detect the different detrimental effects of the environmental conditions on the stone materials and to discriminate among different biofilms and crust from smog or pollutants, in order to optimize the restorers’ interventions. A scanning LIF system at 266 nm excitation wavelength has been employed. The line scanning system has operated in two operating mode: reflectance and fluorescence. Reflectance measurements are made by performing a scan while the laser is off and the sample is exposed to the light emitted by a NIST traceable lamp. The result gives for each pixel of the scanned area the reflectance spectrum, from which the CIE/lab coordinates can be computed once the system is calibrated against a reference surface. The samples were placed on a holder for LIF measurements. The acquisition system was placed at than 3.5 m distance from the target and several images acquired with a spatial resolution of approximately 0.0025 m. The most relevant spectral features of crusts are identified by Principal Component analysis. Three groups of samples can be detected: a) samples with blue false color in the images, that are mainly formed by biocrust, b) samples mainly composed with crust and deposits with yellow or green colour, c) samples with no difference between faces. These classifications of samples are mainly according to the results obtained by morphometric techniques. LIF and reflectance measures seems a very powerful technique in this preliminary results, to discriminate the presence of biocrust and crusts/deposits with more sensitive that a naked-eye at 2.5 m of monuments. © 2014 Taylor & Francis Group, London.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
