Unravelling the mysteries of the fifteenth century ‘Saint Vincent Panels’ by combined in situ and micro-Raman spectroscopy

Abstract

‘The Saint Vincent panels’ are produced by the painter Nuno Gonçalves, and it is a fifteenth century polyptych consisting of six panels. The uniqueness of the work, together with the documentation scarcity about Nuno Gonçalves, highlights the importance of the research of characterizing the colour palette. Raman spectroscopy, both in situ and laboratory instrumentation, was used for this. The mobile Raman spectroscopy campaign is part of the multidisciplinary research project ‘Study, Conservation and Restoration of Saint Vincent Panels’. A mobile EZRaman-I dual Raman analyser (785 and 532 nm) was used during the opening hours of the museum to investigate the panels and their pigments. The polyptych was heavily varnished and as such, the 785 nm laser was preferred for the characterization. It proved to be efficient in characterizing most of the pigments: vermilion, lead tin yellow type I, lazurite, carbon black, gypsum, lead white and calcite were identified. Intervention areas were characterized by the presence of titanium dioxide. Only for a few colours (blue, pink/purple and green), identification with the 785 nm laser was ambiguous and additional characterization with the 532 nm laser was hampered by the strong fluorescing varnish. As a result, micro-samples of these regions were collected for further analysis with benchtop micro-Raman instrumentation. Next to the confirmation of the in situ results, azurite and copper resinate were identified. As such, the combination of both approaches was successful in unravelling the colour palette of the Saint Vincent panels.