Byzantine wall paintings from San Marco d’Alunzio, Sicily: non-invasive diagnostics and microanalytical investigation of pigments and plasters

A diagnostic investigation was carried out on twelfth century Byzantine wall paintings preserved in the Museum of Byzantine and Norman Culture and Figurative Arts of San Marco d’Alunzio (Messina, Italy) on the occasion of recent restoration works. First, the wall paintings were analyzed using portable X-Ray Fluorescence (p-XRF) and Fiber Optics Reflectance Spectroscopy (FORS) to obtain a non-invasive preliminary identification of the original palette. Then, five fragments were sampled for a micro-stratigraphy study using Digital Optical Microscope (DOM), Polarizing Optical Microscope (POM), and Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray Spectrometry (EDS) to characterize the mortars and the blue and black pigments non unequivocally identified through non-invasive techniques. The palette included mainly earthen pigments like red and yellow ochres, green earth, and more valuable lapis lazuli blue applied on a bone black layer; while the analysis of mortars found on the different apses showed the same manufacturing technique and constitutive materials: lime-based binder with the addition of quartz, and rare calcareous lithic fragments as aggregate. The obtained results shed light on the pictorial technique used for the wall paintings and allowed us to compare the Sicilian pictorial cycle with the coeval Byzantine wall paintings preserved in Sardinia and Southern Italy.