Il porgetto di conservazione della cappella di Tas-Salvatur (Kalkara, Malta) : analisi diagnostiche

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The origins of the Tas-Salvatur chapel go back to the 15th century, but historical events brought about demolitions (at the beginning of the Great Siege of 1565 by order of the Grand Master Jean Parisot de la Vallette, and during the uprising against the French in 1798), re-edifications (in 1670 by prior Fra Giovanni Bichi) and interventions over the ages. Inaccessible during past years to parishioners and completely abandoned, the whole chapel is at present the subject of a conservation project carried out by the Malta Center for Restoration within the Cottonera Rehabilitation Project. In the first phase of restoration works, several scientific analyses were performed in order to define the nature of constituent materials and to evaluate the causes and the effects of deterioration processes. Original polychrome layers and repainting were found on the statue of the Madonna with Child situated in the external niche, on the altar, on the overhanging frame and on the sepulchral monument located in the interior of the chapel. Optical microscopy (under visible and UV light), SEM-EDX and FT-IR analysis were carried out identify the painting materials, the remnants of external plastering layers on the facade and the internal ones. Most of the repainting layers are made of lead white (2 PbCO3 PbCO3 Pb(OH)2) and lithopone [BaSO4 + ZnS (ZnO)]. The frame was originally gilded with a guazzo technique and covered later on with several layers of paint. The sepulchral monument in memory of Fra Giovanni Bichi was originally covered with a reddish layer of ochre on stone, while the central framed medallion and the relief portrait of the deceased were gilded (a missione). Below, on the lion's head that forms the lower part of the coat of arms, a brilliant vermilion red (HgS) was revealed under the gray repainting layers. Distribution of salts in the external masonry was evaluated and quantitative data were obtained by means of IC analysis. Tests for the extraction of salts were performed on the lower part of the altar. Sulphatation processes were found where subflorescences of gypsum are the main cause of the loss of stone material (flaking).