Gleaming White. A Newly Discovered Medieval Artificial Lithotype and its Implications for Art Historical Research and Mosaic Conservation

Medieval opus sectile pavements and marble decorations in Southern Italy are characterized by the use of white tesserae obtained from an artificial material called stracotto, employed as a substitute for the natural white stone known as palombino, which was instead derived in the Middle Ages exclusively from classical spolia. More recently, thanks to the efflorescence of the material induced by ultraviolet light, it has become possible to detect its presence in the mosaics of several monuments of Norman Palermo, including the astonishing six-thousand square meters mosaics of the Cathedral in Monreale (near Palermo). The historical contextualization of the artificial white stone identified as stracotto is required at this point; it will be possible only through extensive sampling and identification of white tesserae on Medieval Mediterranean mosaics and archaeometric experimental lab-analyses. Aiming to contribute to this future achievement, this article presents some hitherto unpublished data coming from onsite research.