Portable Sequentially Shifted Excitation Raman spectroscopy as an innovative tool for in situ chemical interrogation of painted surfaces

We present the first validation and application of portable Sequentially Shifted Excitation (SSE) Ramanspectroscopy for the survey of painted layers in art. The method enables the acquisition of shifted Ramanspectra and the recovery of the spectral data through the application of a suitable reconstructionalgorithm. The technique has a great potentiality in art where commonly a strong fluorescence obscuresthe Raman signal of the target, especially when conventional portable Raman spectrometers are used forin situ analyses. Firstly, the analytical capability of portable SSE Raman spectroscopy is critically discussedusing reference materials and laboratory specimens, comparing its results with other conventional highperformance laboratory instruments (benchtop FT-Raman and dispersive Raman spectrometers with anexternal fiber optic probe); secondly, it is applied directly in situ to study the complex polychromy ofItalian prestigious terracotta sculptures of the 16th century. Portable SSE Raman spectroscopy representsa new investigation modality in art, expanding the portfolio of non-invasive, chemically specific analyticaltools.