An archaeometric study of wall paintings in St. Angelo in Criptis cave (Santeramo in Colle, southern Italy, BA): a tool for restoration and enhancement of the site

The St. Angelo in Criptis cave (Santeramo in Colle, Bari) is a suggestive and still active natural karst cavity located in the National Park of Alta Murgia (Apulia, south of Italy). It belongs to a wider and more complex medieval structure, locally known as Iazzo St. Angelo, which consists of three adjacent buildings covering the entrance of the cave and, partially, the cave itself. The complex was initially used as church and after as manor farm. The cavity in the underground space was firstly probably devoted to the pre-classical “cult of water”, later converted to Christianity and entitled, in the early Middle age, to St. Michael the Archangel. Some fine, stratified frescos enrich the cave. They mainly consist in three wall paintings, portraying (i) the Descent of the Holy Spirit and the Christ Pantocrator (two pictorial phases), (ii) the Virgin and Child flanked by St. John and the St. Michael (two pictorial phases), and (iii) the St. Michael Archangel slaying the dragon. Actually all the paintings are in very precarious conditions and needs urgent restoration. Attempt of dating concerns exclusively the Christ fresco, constituded by two pictorial phases, and for which the palaeographic font analysis collocated the oldest painting in the late 12th and early 13th Century and the most recent one, between the 13th and 14th Century. This study, financied by the "Fondazione Cassa di Risparmio di Puglia" with the project "La grotta di Sant'Angelo in Criptis a Santeramo in Colle (BA): studio dello stato di conservazione e valutazione della stabilità", focused on the archaeometrical investigations of paintings with the aim to characterise raw materials, palette of colours and painting technique of pictorial layers and to provide a meaningful contribute to the historical and chronological knowledge of the cave. Paint layers and theirs supports were investigated by optical microscopy, scanning electron microscopy equipped with Energy Dispersive System, Raman spectroscopy and X-ray diffraction techniques. Samples from the Virgin and from the Christ paintings confirmed the existence of the observed two different pictorial cycles, whereas only a paint layer characterised the St. Michael Archangel painting. Archaeometrical analyses allowed to recognize four different types of supports and to highlight strong analogies between the more recent cycles of both the Christ and of the Virgin paintings. All the colours present in the paintings resulted by the mixing of simple pigments like ochres (red and yellow) and carbon, which were mixed in different way to obtain pale or dark colours and/or to produce secondary hues. Interesting is the finding of the cinnabar pigment in the blue of the Pantocrator mantle belonging to the first cycle of the Christ painting. This is a very uncommon finding among pigments used in rock paintings, and could be considered indicative of a period in which the site was an important cultual centre