Statistical processing of IR data for the definition of an integrated protocol in the analysis of geomaterials

The characterization of geomaterials in archaeological and architectural contexts plays a crucial role in understanding their origin, composition, degradation processes, and conservation strategies. Infrared (IR) spectroscopy is a widely employed technique for the analysis of geomaterials, providing preliminary information about the composing mineralogical phases [1]. However, the heterogeneous nature of the geomaterials used in the field of cultural heritage sometimes negatively affects the interpretation of spectroscopic data, resulting in numerous and broad peaks (often overlapped) and shoulders, which are very difficult to be resolved. In addition, portable IR instrumentation should be preferred in the analysis of cultural heritage as it shows numerous advantages due to its non-destructiveness and non-invasiveness and the possibility to acquire data on site. However, there are significant drawbacks in the spectral interpretation as the reflectance spectra differ from those obtained by attenuated total reflection (ATR) or in transmission mode due to the distortions present [2,3]. Consequently, the interpretation of vibrational profiles is difficult, and the absence of a large database have determined its limited application in the field. A chemometric approach is here proposed in the elaboration of IR spectra of various geomaterials analyzed. Indeed, the chemometric approach, by highlighting even minimal spectral variations (caused by a different mineralogical-petrographic and chemical composition), can provide useful information on the nature of the raw materials, provenance, and variations over time, allowing the monitoring of degradation. The present work aims at evaluating the statistical processing of IR spectra of archaeological ceramics, mortars and marbles (from different archaeological contexts), acquired in transmission mode, macro-ATR and external reflectance to assess their potential use in defining the origin of raw materials, production techniques and conservation state. In addition, the comparison among spectra acquired in different modes will allow to create a comprehensive database of reference reflectance spectra for different geomaterials with known composition. The final step will be the possibility to establish standardized protocols which will ensure consistency and reproducibility across different studies, facilitating data comparison and collaboration between researchers. Finally, the possibility to adapt the developed approach in other fields, such as geology and material science, could broaden the impact of the research and contribute to advancements in various discipline.