Insights into the stratigraphy and palette of a painting by Pietro Lorenzetti through non-invasive methods

Paintings are complex multi-layered structures characterised by high compositional and structural heterogeneity. Therefore, a combined analytical approach is often required to overcome ambiguities in the interpretation of data acquired by an individual technique. In this paper, we applied three non-invasive imaging techniques for the study of a 14th-century altarpiece by Pietro Lorenzetti belonging to the Uffizi Galleries. In detail, we used reflectance imaging spectroscopy to identify and map the pigments, and reveal features not visible to the naked eye; to quantify the colorimetric differences induced by the cleaning; to visualise and measure the micrometric thickness of the paint layers. Then, we applied optical coherence tomography to visualise and measure the micrometric thickness of the material layers. Finally, we carried out fluorescence lifetime imaging to discriminate the pictorial integration from the original painting using a method never before applied to a work of art. The data was discussed within a multidisciplinary team of experts.