Zurbarán attribution hypothesis supported by pigment analysis and multiband images observation of four paintings by his workshop

Francisco de Zurbarán was one of the greatest painters of the Spanish Golden Age, with artworks scattered all over the world. Unfortunately, there are hardly any exhaustive studies on the pigments that he used. In this work, four canvas paintings attributed to the Zurbarán Workshop were studied. Each of them presents the figure of a different saint in a particular isolation scene: Saint Bruno, Saint Francis of Assisi, Saint Dominic of Guzman, and Saint Peter Martyr. Nevertheless, the painting of Saint Peter Martyr shows superior quality in both technique and colours, so it is not clear whether this canvas was also made by the Workshop or by Zurbarán himself, as some art historians claim. Coinciding with conservation and restoration works, the paintings were initially analysed with non-invasive techniques such as ultraviolet photography (UV), infrared reflectography (IRR) and X-ray fluorescence (XRF) to determine the characterization of the pigments. Those studies were complemented by stratigraphic analysis of some extracted samples with optical microscopy (OM) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX). Among a number of results obtained, we found significant differences between the pigment palette used in Saint Peter Martyr and the other paintings, supporting the hypothesis that this painting was done by Zurbarán himself instead of his workshop. These results could also help to distinguish other authentic paintings by the master’s hand from very similar paintings by his workshop or by other artists.