Some Examples of Experimental Diagnostics and Conservation Assessments for Planning the Maintenance and Promotion of Rock Art in the Hypogeal Churches of the Apulia Murgia (Southern Italy)

This paper describes the initial research results from the ongoing S.H.I.E.L.D. (Saving Heritage through Imaging and Environmental Long-term Diagnostics) project (2025-2027), implemented by the private business group Tecnosoft S.r.l., e.RATIO S.r.l., and Geoatlas S.r.l., the latter with the scientific support of the Polytechnic of Bari, Department of Architecture, Construction, and Design, through a study agreement. In the Apulian-Lucanian Murgia region (southern Italy), there are a large number of sacred sites associated with rock settlements. These sites contain numerous frescoes dating from the 6th to the 15th century, representing an artistic and cultural heritage of medieval European art that must be preserved. Since these sites are often located in natural settings, such as the vertical walls of ravines or the underground beneath farms and/or churches, and are dug inside the calcarenite banks, they are subject to biological attack by mold, bacteria, algae, and small vegetation. The physical properties of calcarenite, such as porosity and hygroscopicity, combined with concomitant environmental, temporal, biological, chemical, physical, and anthropogenic factors, lead to irreversible multiple degradation. The intensity and speed of deterioration of the frescoes is strictly dependent on external factors such as environmental conditions. The S.H.I.E.L.D. project aims to establish predictive diagnostic protocols for risk conditions through the application of targeted indirect investigations (multispectral images and environmental information) that can guide conservation programming and project. These investigations provide precise information on the health of the investigated elements and enables predictive identification of the specific causes of active degradation, minimizing direct investigations involving the removal and destruction of original material. The detection principle we are testing exploits the physical property of objects to emit or reflect radiation at different wavelengths, in addition to visible light, with intensity depending on their chemical and physical characteristics. Based on this, using a specific and innovative algorithmic model, we aim to identify a correlation between the output of multispectral frames taken on frescoed walls and the presence of one or more causes of degradation. Specifically, the project aims to develop a new predictive technological system that, based on appropriate sampling, can help identify the main causes of degradation, such as water infiltration into the walls and the presence of chlorophyll-rich microalgae. Based on the same principle of reflectance, we will attempt to associate the formation of calcareous concretions or large salt crystals, or the presence of bacteria via their metabolites and catabolites, in the texture of the frescoes and the underlying substrate. At its current stage, the project has selected two characteristic sites for which it has developed a sampling of analyses to determine the diagnostic approach to be tested on a significant number of rock sites located in the Puglia and Basilicata regions. This will validate the methodology on different types of supports, environmental conditions, and exposures. The study presented here begins with specialized instrumental surveys of the two sites, which have very different environmental conditions, followed by visual interpretation of the conservation data and preliminary scientific diagnostics.