Integrated IR multi-methods protocol for Cultural Heritage geomaterials: evaluation of statistical data processing

The study of geomaterials in archaeological and architectural contexts is fundamental for understanding their origin, composition, degradation processes, and conservation. Recent advancements focus on the development and application of innovative scientific methods to study and preserve these materials, while minimizing damage to artifacts. This work combines two approaches: the application of infrared (IR) spectroscopy for geomaterial characterization [1] and the development of a novel protocol under the PNRR project “CHANGES.” IR spectroscopy provides critical insights into mineralogical phases in geomaterials but is often limited by the complexity of the samples, which produce broad and overlapping spectral peaks. Portable IR instruments offer non-invasive, on-site data acquisition, yet their reflectance spectra differ significantly from those obtained via attenuated total reflection (ATR) or transmission modes due to distortions [2,3]. To overcome these challenges, a chemometric approach has been proposed, capable of detecting subtle spectral variations and providing information on raw material provenance, production techniques, and degradation monitoring. Inside Spoke 5 of PNRR project “CHANGES” is developing a new protocol to analyze and interpret geomaterial data. To validate the protocol, various natural and artificial geomaterial samples were exposed to natural and artificial ageing. These samples were analyzed monthly using three Fourier transform infrared spectroscopy (FTIR) methods: ATR (FTIR-ATR), μTransmission (μ-FTIR), and external reflection (ER-FTIR). While the first two methods are micro-invasive, ER-FTIR is entirely non-invasive, making it particularly valuable for Cultural Heritage studies. A multivariate statistical analysis was applied to the IR spectral data to assess the protocol's efficacy in determining raw material characteristics and the progress for degradation processes. The comparative analysis of spectra obtained also aimed to create a comprehensive reference database. This database would enhance data reproducibility and facilitate cross-study comparisons. These advancements enhance the characterization and monitoring of geomaterials while offering broader applications in geology and material science, marking a significant step in the preservation and understanding of Cultural Heritage. This work is financially supported by the project "Cultural Heritage Active Innovation for Sustainable Society (CHANGES)" - Avviso Pubblico n. 341 del 15/03/2022 - Piano Nazionale di Ripresa e Resilienza - NextGenerationEU - PE0000020 - CUP: B53C22003780006 [1] V. Brunello, C. Corti, A. Sansonetti, C. Tedeschi, L. Rampazzi, Non-invasive FTIR study of mortar model samples: comparison among innovative and traditional techniques, The European Physical Journal Plus 134 (2019) 270. [2] L. Nodari, and P. Ricciardi, “Non-invasive identification of paint binders in illuminated manuscripts by ER-FTIR spectroscopy: a systematic study of the influence of different pigments on the binders’ characteristic spectral features”, Heritage Science, pp. 1-13, 2019. [3] C. Miliani, F. Rosi, A. Daveri, and B.G. Brunetti, “Reflection infrared spectroscopy for the non- invasive in situ study of artists’ pigments”. Applied Physics A, pp. 295-307, 2012.