Insight into Baccio da Montelupo's wooden crucifix. A multi-analytical approach

The Jesus Christ wooden crucifix hosted in the Church of San Casciano Val di Pesa, near Florence, is an exquisite example of the Italian Renaissance polychrome sculpture (Fig. 1a). It was created at the beginning of the XVI century and it is attributed to the Florentine sculptor Baccio da Montelupo. In the early months of 2016, a thorough restoration started for conservative and aesthetic purposes, aimed at uncovering the original pictorial surfaces hidden by old retouches and aged varnishes, and intervening against the attack of xylophages insects. A diagnostic project was set up to characterize the materials used, the artistic technique, the state of conservation and the internal structure of the statue through non-invasive methods. The surface was documented with UV photographic imaging, while pigments and varnishes/binders were investigated with portable instrumentation by using X-ray fluorescence (XRF) and Fourier-Transform Infrared (FT-IR) spectroscopy, respectively. The presence of repairs and metallic structures, as well as the assembly of the wood panels, were also investigated with Computerized Tomography (CT, Fig. 1b). The cleaning steps were monitored repeating photographic UV documentation and FT-IR analyses (Fig. 1c-d). The UV photographic essay showed the abundant presence of a strongly fluorescent varnish, that makes completely invisible the underlying materials such as the blood on part of the forehead and on the chest and the decoration of the perizoma. However, elemental analysis performed by XRF highlighted the presence of high counts of lead (Pb), related to the use of biacca, excluded the use of cinnabar on the blood drops and showed how the decorations on the perizoma were made of gold. CT images revealed, inside one leg, hyperdense and probably metallic structures, whose function is still not clear. From FT-IR analysis it was possible also to hypothesize the presence of siccative oils as binders, a natural resin as varnish and a waxbased protective coat.