Combining diffractometric and spectroscopic analysis of artificial stones from Palazzo Brasini (Taranto, southern Italy) to characterize materials and constructive systems

The aim of this work is to give a compositional characterisation of the artificial stones used in the building up of the Taranto (Apulia region, southern Italy) seaplane station, also better known as Palazzo Brasini (named after the architect who designed it), which represents an example of eclecticism from early 20th century monumental style. Diagnostic analyses applied to architecture, and specifically to “artificial stone” - carried out by combining diffractometric technique with spectroscopic ones, i.e. micro-Raman spectroscopy and micro-X-Ray fluorescence – provided information related to the compositional characterization of the material and its mechanical characteristics. They resulted to be compulsory to decode the specific production processes adopted by artisans other than to provide useful information on the interaction between the artefact and the conservation environment and the identification of degradation processes, thus allowing to plan any further restoring protocol. Besides, diagnostic analyses were necessary to highlight the technological know-how and the circulation of knowledge of artificial stone productions by identifying the lithocement components. The main artificial stone production features regard the use of saffron as a colouring agent in the production of the artificial stones of Palazzo Brasini due to its toxicological safety and stability to light. The use of this pigment is in line with the autarkic style that characterises the architecture of the 20th century, because it prefers the use of local or at least easily found raw materials. Grossularia, iron oxides, and carbon black were also used as pigment in the adopted artificial stones from Palazzo Brasini and their presence, together with that of saffron, can be likely considered a sort of “trademark” of manufacturing. Chloride ions have been found in the northern facade of the Palazzo Brasini as consequence of it being set in an environment where chloride rich aerosol is remarkable. It was found in samples from the external wall finishing layer from both the lower moulding and the upper moulding. The presence of chlorine in the layer of smooth plaster, suggests a slight penetration of the ion up to the smooth plaster. Besides, the penetration of sulphur into plaster layers (“arriccio” and smooth) – likely associated to the mineralogical phase gypsum as suggested by Raman spectroscopy – is responsible for the transformation reaction of calcite into anhydrite and may be related to the natural acidity of rainwater/aerosols and physical weathering from temperature change and erosion. The observation of white efflorescence, in between the sublayer A and B of the external wall finishing layer from lower moulding and upper moulding it is likely a consequence of the aggressive environment is which Palazzo Brasini is set. The proximity to the steel plant ILVA, responsible of high SO2 concentration levels in the aerosol, can be the triggering factor of the sulphate attack on the upper and lower moulding.