Diagnostics
An intensive diagnostic phase is the basis of any intervention: all the investigations carried out were put in relation to each other, to arrive at the formulation of the best conservation and restoration systems.
The investigations on the structure served to identify discontinuities in the rock, possibly responsible for infiltrations and consequent damage; connected to these was the study of environmental parameters, with microclimatic monitoring, aimed at assessing thermo-hygrometric variations inside the church.
Investigations on the products of neo-formation found, were useful to define their nature in relation to the environmental context.
Analyses on the colours were carried out in order to provide the most comprehensive set of information on the original execution techniques.
During the restoration works of the wall paintings, the Church of Santa Lucia alle Malve remained open to the public, with a site visit programme dedicated to tourists.
Structurale investigations
Georadar and thermovision
The examination was conducted outside, on the rock plateau over the church, and inside, on the ceiling to assess the presence of discontinuities in the rock, possible routes of infiltration of rainwater into the interior of the church. This investigation was flanked by a thermographic survey, to visualise the thermal distribution of the surfaces, and the identification of any areas with higher water content.
The circulation of infiltrated water along the thickness of the rock is one of the causes of the formation of salt efflorescence on the interior walls, as well as biological patinas.
Study of environmental parameters
Photographic and HDM video footage was taken from a drone in order to obtain a photo-mosaic of the rock plateau: with the aim of identifying the relations of continuity between the interior and exterior, the plan of the church was superimposed on this image.
During the months of September 2019 to February 2020 and until December, at the same time as the conservation work was carried out, the temperature and relative humidity trends were monitored and the dew point temperature was calculated.
During the monitoring period, it was observed that the values of the thermo-hygrometric parameters vary mainly in relation to external weather conditions and, consequently, to the opening and closing of the church entrances.
The graphs show, in fact, that while the temperature varies slowly in relation to seasonal weather conditions, the relative humidity, while remaining constantly high, is subject to variations, sometimes considerable, favouring evaporative phenomena responsible for the formation of veiling (salts) on the painted surfaces. This situation is common to all hypogeal or semi-hypogeal environments, for which scheduled maintenance must be carried out periodically. The study was completed with lighting and air quality control.
Alteration products
Biological characterisation
Biological attacks were evidenced by patinas of consistent thickness, in the order of millimetres, with various colourings. Through micro-bliological investigations, five different types of biological patina were identified.
Salts
FT-IR micro-spectroscopy imaging analyses were carried out on different areas to identify the component materials of the whitish patina present at the scene of the Deposizione.
The diagnostic analyses revealed that the patina consisted of silicates and calcium carbonate. The presence of nitrates was also detected in the patina. Based on the results obtained, it can be assumed that the silicates contained in the wall structure were transported to the surface through water infiltrations. This long-term effect may lead to the formation of white encrustations of silicon dioxide (opal) or silicate mixed with other substances, in particular calcium carbonate.
Colours
The instrumental investigations carried out, add interesting data, useful for reconstructing the ancient painting techniques employed. Of particular interest was the discovery of traces of two precious pigments: azurite and minium. Azurite is found in traces in various areas; in particular, it was used to reproduce the precious stones that enrich San Michele’s robe, and is also found on the surface surrounding the halo of San Vito. Images taken with a hand-held microscope at 200 x show the crystals typical of azurite; the finding is confirmed by the diagnosis on micro-samples.
Through infrared optical investigation in false colour and ultraviolet light, minium was detected in the lips of San Vito‘s face, as well as in his cape. Minium also appears in the robe of San Michele Arcangelo, used to make other gems that adorn it. In only one sample was the ultramarine pigment was detected.
