A multi-analytical approach for the characterisation of the oldest pictorial cycle in the 12th century monastery Santa Maria delle Cerrate

A multidisciplinary research, currently in progress at the University of Salento in collaboration with the Lecce Provincial Museum, interests different artistic expressions widespread in the Salento peninsula (South Italy). In the present study, the characterisation of organic and inorganic materials used in the oldest pictorial cycle found in the 12th century monastery Santa Maria delle Cerrate was carried out thanks to a multi-analytical approach. Previous investigations have focused on the problem of dating the frescoes mainly on the basis of the stylistic aspects and the material characterisation has been definitely underinvestigated. Chromatographic and spectrometric techniques were used: micro-Raman spectroscopy was used for recognising pigments and gas chromatography with mass spectrometric detection for analysing organic binders. These techniques enabled us to characterise pigments and binders. The presence of both true fresco and tempera bound pigments was assessed. Among the different pigments detected, the results relevant to the blue paints were interesting: two different blue pigments were, indeed, identified, lapis lazuli and smalt (cobalt blue glass) both unexpected. As a result, Santa Maria delle Cerrate appears to be the first known example of their use in South Italy. From a conservation point of view, moreover, the knowledge of the palette permitted to highlight the reason of observed decay of some paints: for instance, lead white was used in some panels, explaining their blackening.