Monitoring hypogeum systems affected by crystallisation processes among conservation needs, microclimate factors and accessibility to heritage

The scientific research project HYPOGEA started in 2012 by the Pontifical Commission for Sacred Archaeology (PCAS), Vatican, and ICVBC-CNR, Florence, aims to understand the processes of calcium carbonate crystallizations that commonly cover the painted and rock naked surfaces in Roman catacombs, and assess the influence exerted by the environmental conditions and their trend changes. Microclimate monitoring of the Cubicle of the Twelve Apostles in the catacombs of Saints Mark, Marcellian and Damasus by means of a sensor network is coupled with periodic surface pattern change detection. The latter is carried out by combining non-invasive techniques (e.g., colorimetric measurements and digital micro-photogrammetry) and laboratory investigations (e.g., thin and cross-section, FT-IR, XRD and ESEM analyses) on samples taken from both ancient surfaces and newly applied frescoes. The first outcomes are providing interesting insights into the operational issues involved in the monitoring of such unusual environments, including for instance the choice of the parameters to take into account, as well as the materials to use for in-situ experimentations (e.g., pigments and methods and time of application). Monitoring is assumed here as a mean towards a long-term preservation plan, with the perspective of a feasible balance between the aspects of conservation and those of promotion of this hypogeum painted heritage.