Archaeometric study of wall rock paintings from the Sant’Angelo in Criptis cave, Santeramo in Colle, Bari: insights on the rupestrian decorative art in Apulia (Southern Italy)

The paper deals with the archaeometric investigation of wall paintings in the Sant’Angelo in Criptis karst cave in Santeramo in Colle (Southern Italy) dedicated to St. Michel the Archangel. The investigated wall paintings portray the Virgin with Child, the Christ Pantocrator and Descent of the Holy Spirit, both consisting of two overlapped pictorial cycles, and St. Michael the Archangel slaying the dragon, containing a single painting. Archaeometric research focuses on the characterisation of 56 samples of mortars and pictorial layers in terms of raw materials, pigment mixtures and painting techniques and aims to provide a meaningful contribute to the historical and chronological knowledge of the site. The analytical approach involved microstratigraphic observation under reflected-light optical microscope and compositional characterisation through micro-Raman spectroscopy and scanning electron microscope-energy dispersive X-ray spectroscopy. Results indicated a colour palette involving shades of red, yellow and black, obtained using common pigments such as red and yellow ochres and carbon black frequently mixed to each other, or with lime, to produce secondary hues and most precious pigment, as cinnabar. Mortar analysis provided information on technological aspects and helped to validate chronological hypotheses. The most relevant aspect emerging from results was the custom and the ability of the workers to mix few pigments to obtain several shades and chromatic nuances and the competence in the overlapping of different coloured layers to produce specific chromatic effects. Such considerations suggested the modus operandi of the artists who worked in the Apulia region in the Middle Ages and helped to define technical procedures and material features of the Apulian rupestrian paintings.