Comprehensive ir multi-method approach for mortars of cultural heritage interest

The characterization of mortars in archaeological and architectural contexts is mainly focused on defining the composition, the provenance of raw materials, the degradation products and the causes that led to their degradation. In the last decades, the scientific community has turned to find methodologies and innovative scientific techniques for the analysis and monitoring of these materials, to minimize as possible the sampling and the damage of the works of art. Among the widely methods in the Cultural Heritage Science, IR spectroscopy provides information regarding the mineralogical composition of geomaterials (Brunello et al., 2019), although its effectiveness can be limited by the complexity and the heterogeneity of samples, resulting in broad and overlapped bands. Even if portable IR instruments enable non-invasive on-site data collection, making it especially valuable for Cultural Heritage studies, the obtained reflectance spectra differ significantly from those obtained using attenuated total reflection (ATR) or transmission modes (which requires micro samples) due to spectral distortions (Miliani et al., 2012; Nodari & Ricciardi, 2019). To evaluate the applicability of ER-FTIR in the study of complex heterogeneous materials as the mortars, ATR, μTransmission (μ-FTIR), and external reflection (ER- FTIR) have been combined with a chemiometric approach and the results have been compared. The ER-FTIR combined with Principal Component Analysis (PCA) elaboration has been evaluated analysing these artificial geomaterial samples, and check if the results helped in defining the raw material provenance, the production techniques. In addition, some samples have been natural and artificial aged and monthly monitored to evaluate the protocol’s effectiveness in monitoring degradation progress. The comparative analysis of the spectra collected aimed to create a comprehensive reference database, enhancing data reproducibility and enabling easier cross-study comparisons. These developments not only improve the characterization and monitoring of geomaterials but also broaden their applications in fields like geology and materials science, marking a crucial advancement in the preservation and understanding of Cultural Heritage. As example of the real application of this multi-method approach, a real case study based on mortars from the Holy Sepulchre in Jerusalem. 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 Brunello V. et al. (2019) - Non-invasive FTIR study of mortar model samples: Comparison among innovative and traditional techniques. The European Physical Journal Plus, 134(6), 270, https://doi.org/10.1140/epjp/ i2019-12667-1. Nodari L. & Ricciardi P. (2019) - 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, 7, 1-13. Miliani C. et al. (2012) - Reflection infrared spectroscopy for the non-invasive in situ study of artists’ pigments. Applied Physics A, 106, 295-307, https://doi.org/10.1007/s00339-011-6708-2