Raman mapping and time-resolved photoluminescence imaging for the analysis of a cross-section from a modern gypsum sculpture

This work proposes a non-destructive multi-analytical approach, based on Raman and photoluminescence mapping to characterize the constituent materials and the stratigraphy of a multi-layer sample from a 19th century sculpture by Pompeo Marchesi. The study exploits a macro-Raman device, capable of mapping heterogeneities on a scale from sub mm2 to cm2 without the need for refocusing. The combination of the macro-Raman probe with a more conventional micro-probe improves the quality of Raman spectra and allows the material identification with a high level of confidence. Time-resolved photoluminescence microscopy allows the mapping of photoluminescent centres in the micro-sample, ascribed to crystal defects in inorganic materials. The proposed combination of optical analytical techniques provides an in-depth characterization of the constituent materials of the sample, yielding insights on its conservation history. The protocol could be potentially extended to the analysis of cross-sections of paintings.