Direct study of natural stone materials of historical architecture in the context of the deposit for rubble of cultural interest in seismic emergency

The study of natural stone materials in the field of cultural heritage is of strategic importance for the preservation of historic architecture. The interest of the scientific community concerns the entire process, from quarrying, processing, construction, aging, degradation and conservation needs. Usually, the direct study of the material is possible in the preliminary stages and during the restoration. In some exceptional cases, it is possible to have a lot of material and for a long time, as happens for example following a seismic event. With the MiBACT Directive 12/09/16, “Procedures for the removal and recovery of the rubble of protected and historic buildings”, temporary deposits were established for the first time, to set aside the rubble deriving from the collapses. As they are currently organized, the deposits for the rubble are places of orderly storage of materials of cultural interest, assigned to their custody, in the time that elapses between their removal and their possible relocation on site. The materials arriving in the rubble deposit are not particularly perishable and do not need thorough checks on their state of conservation. However, the diagnostic study in the rubble deposits represents a procedural improvement for its intrinsic knowledge value and for the subsequent activities of restoration, on site relocation of the materials or their musealization. As already happened for the reconstruction of the Cathedral of Venzone, following the earthquake that struck Friuli in 1976, the preparatory study of the individual stone elements, including archaeometric data such as morphology, metric data, petrographic data and the characterization of degradation, proved to be fundamental for the post-emergency conservative phases. This contribution illustrates some operational proposals for the scientific study of natural stone materials from collapses of historic buildings, to be carried out inside the deposits and shows the results of a coherent experimentation conducted at the deposit for the rubble in Rieti on some remains from the church of Sant’Agostino in Amatrice. Specifically, the study was conducted on the pieces of the portal and the rose window and led to the acquisition of significant data regarding the construction and conservation history of the two elements. The diagnostic investigations conducted on site were: the characterization of the materials by digital optical microscopy, the study of the traces of processing of the materials by photographic shooting in grazing light, the study of the residual traces of painting by colorimetric tests, the observation of materials in UV light. From the cross-reading of the diagnostic data it was possible to discern the original materials of the portal from restoration ones, also estimating the different resistance of both materials and the resistance of the anchoring system of the restoration elements. Those characteristics determined distinct responses to seismic stress. About the rose window, dated from historical documentation to 1933, the analysis of the stone elements has identified 17 elements belonging to an older rose window, thus documenting a case of reuse of ancient decorative stone materials, previously unknown.