Abstract
Plasters and mortars of the Church of the Annunciation (Tortorici, Sicily) were characterized, for the first time, both at the elemental and molecular levels, by means of portable X-ray fluorescence (XRF) and Raman spectroscopy, to achieve information on the “state of health” of the whole structure. The understanding of their degradation mechanisms and the identification of consequent degradation patterns can define the environmental factors responsible for interpreting the potential pathological forms that can impact the general building vulnerability. In this sense, the results obtained in this article provide relevant information to identify and address both the characterization of building materials and the fundamental causes of their deterioration. At the same time, if coupled with the attempt to supply a chronological order of the major restoration interventions carried out on the investigated site, they provide new insights to calibrate the models for building vulnerability studies.
Highlights
The importance of multi-technique characterization of materials [1] is linked to the possibility to evaluate, on one side, any change in their physical state starting from the production of the specimen from the raw geological/mineralogical materials, and, on the other side, their diffusion through trade, use, and deployment in the archaeological record.In the variety of techniques employed in different research areas of archaeometry [2,3,4,5], X-ray fluorescence (XRF) spectroscopy has an extensive use, being a well-established analytical method both in the laboratory and industry for the evaluation of the elemental composition
As far as the preparation ground is concerned, identified as point PG, the Raman spectrum collected on it (Figure 2) revealed an intense peak at ~1080 cm−1, along with other contributions at ~162, ~282, ~712, and ~1435 cm−1, all associated to the presence of calcite, the most stable polymorph of calcium carbonate (CaCO3) [17,18,19]
The use of white lead as the main component to prepare the gray pigmented plaster [21] can be hypothesized, mixed with Fe3O4 and other iron oxides as black pigments. This can justify the high concentrations of Pb and Fe detected by XRF in the corresponding area
Summary
The importance of multi-technique characterization of materials [1] is linked to the possibility to evaluate, on one side, any change in their physical state starting from the production of the specimen from the raw geological/mineralogical materials, and, on the other side, their diffusion through trade, use, and deployment in the archaeological record.In the variety of techniques employed in different research areas of archaeometry [2,3,4,5], X-ray fluorescence (XRF) spectroscopy has an extensive use, being a well-established analytical method both in the laboratory and industry for the evaluation of the elemental composition. Many alternative techniques require dissolution procedures that are both time-consuming and costly in terms of the acids or other reagents required [6]. Raman spectroscopy is another analytical technique widely used in archaeometry [7,8], offering the advantage that, being a molecular spectroscopic technique, it can deal with inorganic and organic materials [3], including ancient objects and modern artists’ specimens [7].
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