Multianalytical investigation of pigments in the Madonna della Croce wall painting (Triggiano, Italy)

The Madonna della Croce portrait is painted on a lunette, previously detached from a wall of unknown origin and now preserved on the right of the main altar in the Madonna della Croce church, in Triggiano (Bari, Italy). The wall painting, which depicts the Virgin and Child with St. Sebastiano and St. Rocco with their symbols of martyrium, was realised by a local artist who worked between 1550 and 1570 in the town. The numerous legends about the wall painting, mixed with historical events, talk about miraculous healing stories which has strengthened the strong relationship of the Triggiano inhabitants with this religious symbol, such as they built a dedicated church and chose this Virgin as patron Saint of the town. The presented research mainly focusses on the investigation of pictorial layers of this painting by a non-invasive multianalytical approach. Firstly, shape, size and optical features of pigments have been observed using a portable digital microscope equipped by a polarizing filter. By means of a portable spectrophotocolorimeter, colour of painting areas has been measured and expressed in the CIEL*a*b* system and for each of them reflectance spectra of visible light (400-700 nm) have been recorded. The identification of pigment composition has been carried out by FORS (fiber optic reflectance spectroscopy) and XRF (X-ray fluorescence spectroscopy). Produced spectra have been compared with databases available in literature. Results have provided information about features and compositions of pigments, highlighting the use of red ochre, yellow ochre and carbon black for red and yellow paintings and for black profiles; in addition, mixing of red ochre and green earth and mixing of carbon black, lime and yellow ochre have been revealed respectively in correspondence to green background and blue Virgin mantle, as attested in other Apulian wall paintings (Fioretti et al. 2020; Fioretti et al. 2020).