Development of advanced SORS protocols and data analysis routines for cultural heritage applications

This doctoral research stems from the need, within the fields of diagnostics and analytical sciences, for non-invasive techniques capable of investigating the depth of materials, especially in the context of cultural heritage applications. Such methods are essential, as much of the information regarding the materials selected by the artist, the artist’s technique, and the conservation history of artworks lies beneath their surface. By integrating material analysis with the historical and artistic dimensions of artefacts, a more comprehensive understanding of the cultural and technological contexts in which they were created can be achieved. Furthermore, an in-depth knowledge of material degradation processes supports the development of more effective preservation strategies, ensuring the long-term protection of heritage objects against the effects of time and environmental factors. In this scenario, the study meetsthis need through the development of methodologically and technologically advanced protocols related to the Spatially Offset Raman Spectroscopy (SORS) and its microscopic variant (micro-SORS), which have already proven to provide specific and non-invasive molecular analysis of the inner layers of materials. In the organization of the thesis, I have selected a structure based on the conceptual progression of the scientific themes explored during my studies rather than following the chronological sequence in which the activities were carried out over the three years. Therefore, the structure mirrors the evolution of the research, from the initial theoretical studies to the experimental validation, and subsequent elaboration and interpretation of the results. The chronological sequence is briefly presented below. In the first year, the course of my doctoral research began following two different research studies: the first was related to the optimization of an in-house portable micro-SORS prototype developed for in-situ cultural heritage applications; the second focused on the non-invasive study of the evolution of pigment degradation below the surface through micro-SORS mapping coupled with map reconstruction routines specifically designed through an in-house developed script. These two research lines were conceived to be instrumental to the single goal of enabling non-invasive in-situ analysis to map the surface and subsurface of the materials. Together, they laid the methodological foundation for the works presented in Chapter 4 and 5.1. The second year was devoted to defining the theoretical and practical boundaries between SORS and micro-SORS, in order to establish criteria and protocols that could help selecting the method to employ in various cultural heritage scenarios. Moreover, as on field measurements are very common in many analytical sciences, a research related to the rejection of both static and dynamic ambient light contributions during Raman and SORS in-situ measurements was carried out throughout the second year. An abroad research period at the Central Laser Facility of the Rutherford Appleton Laboratory (RAL, Harwell Campus, Didcot, UK) was set specifically to shed light on these matters. These works, shown in Chapter 2 and 3, jointly expand our understanding of the theoretical background and the techniques to employ for on-field diagnostic campaigns. During the third year, I carried out another research period abroad at the University of Cincinnati (Ohio, USA) related to the implementation of machine learning (ML) in data analysis routines for heritage science applications. Through the map reconstruction routine designed in the first year for the non-invasive study of subsurface pigment degradation, a comparison between experimental outcomes and ML results was thoroughly investigated to provide a reference-free and automated method to estimate the extent of degradation in artworks. This work is presented in Chapter 5.2. Additionally, during my PhD I attended multiple analytical campaigns within the E-RHIS (European Research Infrastructure for Heritage Science) infrastructure to improve my on-field experience and keep an application-oriented mindset towards research. A selection of these case studies is shown in Chapter 6, where the potential of the portable micro-SORS prototype described in Chapter 4 is highlighted. I also had the chance to present our works at multiple conferences with both posters and invited talks, such as SciX 2023 to 2025, Gordon Conference 2024, SIF 2025 and IRDG 2023 internal meeting. Over the course of the three years, I received three awards, namely IRDG Chalmers & Dent 2024 Award, Royal Society of Chemistry 2024 Student Travel Award, and 2025 FACSS Student Award. I also had the opportunity to present two online seminars for the Royal Society of Chemistry (January 23rd 2025), Coblentz Society and the Society of Applied Spectroscopy (July 23nd 2025). The conferences and webinars allowed me to present my work, gather suggestions and foster new ideas through networking and collaborations, and they definitely played a major role in sharpening the methodological approach over which the thesis is built on.