A Portable Micro-SORS Prototype for Cultural Heritage: New Capabilities and Advantages

The combination of Spatially Offset Raman Spectroscopy (SORS) with microscopy has led to the development of micro-SORS, a technique enabling non-invasive analysis of subsurface layers at the microscale, specifically optimized for Heritage Science applications. Here, we present the capabilities and advantages of a recently developed advanced portable micro-SORS prototype, designed to overcome the main limitations of current commercial and custom-built systems. The prototype offers high sensitivity, wide spectral window (100–3050 cm−1) and a simultaneous acquisition of multiple offset spectra via a custom fibre bundle, which also reduces mechanical vibrations. Moreover, an integrated digital microscope allows for an accurate point selection during in-situ analysis of artworks. The system was tested during two analytical campaigns within the MOLAB platform at the Italian node of E-RIHS-ERIC (European Research Infrastructure for Heritage Science): the study of Andrea Solario’s paintings at the Museo Poldi Pezzoli (Milan) and the Book of the Dead of Kha at the Museo Egizio (Turin). The results demonstrate four key capabilities: (i) non-invasive identification of pigments with diagnostic Raman bands in the low-frequency region (e.g., lead-tin yellow type I, anatase); (ii) detection of ground layers, revealing insights into painting techniques; (iii) reconstruction of stratigraphies, including the identification of pigment layering in the papyrus; and (iv) characterization of surface heterogeneity, such as elemental sulphur crystallization linked to arsenic sulphides degradation. These findings confirm the prototype potential as a powerful tool for heritage science, enabling high-quality, depth-resolved Raman analysis directly on artworks. Limitations observed during one year of field use are also reported, highlighting opportunities for future developments.