Hyperspectral sensor: A handy tool to evaluate the efficacy of cleaning procedures

In urban environments, degradation processes affecting both natural and artificial carbonate materials commonly result in the formation of sulphate-based deposits (i.e., black crusts). Hyperspectral techniques may provide ready-to-use information on the degree of sulphation of carbonate stone, hence helping to monitor the conservation state of carbonate stone monuments. In this study, the Short-Wave InfraRed (SWIR) hyperspectral technique was tested on the world-famous marble-made Loggia di Baccio d'Agnolo in Santa Maria del Fiore Cathedral of Florence (Italy), affected by extensive “black crust” formation. A SWIR method based on a portable spectroradiometer (ASD Fieldspec® 3) was applied to verify the efficacy of different cleaning methods (i.e., laser, chemical and microbial). The interpretation of the SWIR spectra was based on a full-profile approach, in which the calcite and gypsum contributions were evaluated by weighing the best fit simulated contributions of reference compounds. The technique was able to provide in real time semi-quantitative determinations of the amount of gypsum developed on the stone surface, demonstrating to be a fast and handy routine tool during restoration of artworks.