Figure 2From: Brownish alterations on the marble statues in the church of Orsanmichele in Florence: what is their origin? San Pietro, attributed to Filippo Brunelleschi, ca. 1421, detail. The brown discoloration visible on the stone surface (a). Fluorescence emission of surfaces after ultraviolet excitation test (b). Fluorescence lifetime imaging results (c). Photographs Opificio delle Pietre Dure.Back to article page