EXTENSIVE PREVENTIVE DIAGNOSTICS FOR BIOCLEANING AND BIOCONSOLIDATION OF TWO RUPESTRIAN CHURCHES

Historical-artistic heritage suffers biotic and abiotic degradation more than in the past due to the increasing environmental pollution. The process of deterioration is progressive and irreversible, and the timing and mode of impact is different depending on the characteristics of the monument (location, orientation, mineralogical and structural properties), microclimate (temperature, humidity, solar radiation, wind regime, precipitations), air pollution (particulate, concentrations of SO2, NOx, CO2), presence of specific flora and fauna on the surfaces. The conservation and recovery of such structures require the understanding of physical-chemical and biological processes causing the deterioration of materials, and the knowledge of restoration strategies [1]. The characterization of structure and microstructure of historical materials is mandatory in preventing, and eventually recovering, degradation effects. Ideally, the analysis of an artwork should be complete, efficient, rapid and, if possible, non destructive when dealing with precious or unique objects. Thus, measurement should be carried out in-situ or by removing very small amounts of material. XRD, XPS, GPR, MGE and FT-IR are some techniques widely applied to study materials used in historical or artistic artefacts. Complying with this purpose, two Rupestrian Church (Santa Lucia alle Malve and San Pietro Barisano) located in Matera town in the area named "SASSI", rich of natural vegetation and biodiversity, were studied in order to carry out the a possible restoration, by using plant secondary metabolites, and bio-consolidation, by using calcinogenic bacteria. Chromatic alteration of the stone surfaces, presence of patinas, sagging, efflorescence and detachment of some portions of plaster and a lush biological colonization were observed, favored by water infiltrations and by particular internal microclimatic conditions. Sampling and characterization of the stone supports were performed. The detached rock fragments were subjected to petrographic and surface analysis by using Xray diffraction technique, SEM - EDS system and X-ray photoelectron spectroscopy(XPS). All analytics showed an advanced state of decay with the formation of degradation products such as sulfates and calcium nitrate. Moreover, the thermo-analysis has confirmed the presence of water on the top and in the wall of the churches structure caused by outside fractures. Glycoalkaloids (secondary metabolites extracted from Solanaceae plants) [2,3] were used for the bio-cleaning. Autochthonous colonizer bacteria found on the building surfaces were used for the stones’ bio-consolidation in situ.