Combined use of vibrational spectroscopy and mass spectrometry techniques for the study of manuscripts and painted surfaces

Artistic manufacts are subject to numerous degradation processes arising from natural aging, visitor impact, biological contamination, and environmental conditions in both indoor and outdoor settings. Analytical chemistry contributes by identifying materials and techniques, diagnosing degradation mechanisms, and developing new conservation methods. The aim of the research was to develop and apply analytical protocols combining vibrational spectroscopic techniques with mass spectrometric methods. The project was carried out at the Department of Chemical Sciences (University of Naples Federico II), the Royal Palace of Caserta, and the Archaeometry Laboratory of Ghent University, in a close collaboration between academic research and museum institutions. The thesis is structured around three main objectives: 1. Diagnosis of written documents, with a focus on the rarely studied carbon–iron gall mixed inks (C-IGI). 2. Study of painted surfaces to identify preparative techniques and later restoration materials. 3. Biomonitoring of emerging contaminants exploring their potential role in the degradation of monumental surfaces. The research employed a multi-analytical and integrated approach, combining several complementary techniques: i) vibrational spectroscopies (Raman micro-spectroscopy and FT-IR spectroscopy); ii) Optical and electronic microscopy (OM and SEM-EDS); iii) X-Ray Fluorescence; iv) chromatography assisted mass spectrometry (HPLC-MS and GC-MS). All analytical procedures were designed to be non-invasive or minimally destructive, in full compliance with conservation requirements. Below are reported the results obtained during the three-years activity. 1. Historical manuscripts and ink degradation The study of Luigi Vanvitelli’s 18th-century letters (Palatine Library, Royal Palace of Caserta) revealed amorphous carbon, metallic sulfates (Fe, Cu, Zn), and iron(III)–gallate complexes, confirming the use of a mixed carbon–iron gall ink. Laboratory mock-ups showed that carbon markedly accelerates iron–gallate degradation: Raman micro-spectroscopy detected the loss of Fe–gallate signals after only a few days of thermal aging, while HPLC-MS identified early oxidation products such as ellagic acid. Carbon promotes ink deterioration by adsorbing gallic acid and destabilizing the iron–gallate complex. These results clarify degradation mechanisms in mixed C–IGI inks and provide new guidance for preserving historical manuscripts. 2. Painted surfaces The analysis of Roman wall fragments revealed the use of a fresco-secco technique, with a secco pictorial layer applied over a fresco mortar preparation, confirmed by the presence of protein-based organic binders. The study of a Roman fresco demonstrated that the preparatory technique can be determined through non- and micro-destructive methods, while macro-destructive analyses provided further stratigraphic confirmation. Spectroscopic and spectrometric analyses of funerary ceramics from a Hellenistic tomb containers identified pigments such as hematite, indigo, and amorphous carbon, as well as silica-based glittering materials and organic binders including vegetable oils and milk. These results suggest that the ceramics held cosmetics and ointments used for the adornment of the deceased. An integrated analytical approach characterized inorganic and organic materials of the polychrome Bourbon floors at the Royal Palace of Caserta, revealing up to four decorative layers and the coexistence of original and modern restoration materials. Two main decoration methods were identified: (i) minium applied directly on terracotta and (ii) stratified preparatory and pictorial layers. The 18th–19th-century layers consist of calcium and barium sulfates with TiO₂ preparations and oil-bound mineral pigments, while 20th-century layers contain barium sulfates with calcium carbonate, pigments, and synthetic resins. This analytical evidence are consistent with the lack of documents in historical archives of the Royal Palace of Caserta, which mention the use of “vernice a olio” e “vernice a spirito”. 3. Biomonitoring of microplastics in heritage environments A biomonitoring protocol for microplastic analysis using mosses and lichens as capturers, previously developed, was applied at six sites within the Royal Green Park of Caserta. Microplastics were extracted from lichens with this protocol, and their chemical identification is ongoing. Preliminary results show clear microplastic presence within black crusts mainly composed of carbonates and sulfate; polymer characterization is in progress. This comparative study confirms the protocol’s applicability to cultural heritage contexts, exploring the possible role of specific microplastic types in black crust formation. Overall, the analytical approach, combining vibrational and chromatographic techniques, demonstrates an effective model of science–heritage collaboration extendable to other European conservation contexts.