Identification of lime-based mural painting techniques in catacombs using well-established criteria of stratigraphic investigation

Well-established criteria of cross-section stratigraphic investigation developed by Piovesan et al. (2012) and the petrographic methodology of classification of surface crystallisations by Tapete et al. (2013a) are integrated and tested on selected set of mural painting samples collected from the Roman catacombs of St. Tecla, Domitilla and Priscilla, Rome, Italy (second half 4th-late 5th centuries A.D.). The main purpose of this research is to assess the suitability of these combined methods to identify the painting technique, thereby overcoming the risk of misinterpretation of the stratigraphic evidences due to effects induced by the microclimate conditions of the hypogean environment at the time of production of the paintings. H₂O-CO₂ exchanges between air and painted surface, and related dissolution-precipitation reactions triggered by surface condensation of CO₂-rich water, tend to alter the former structure of the painting and therefore add textural and stratigraphic features that combined optical and scanning electron microscopy observations can successfully detect.