Raman and time of flight secondary ion mass spectrometry investigation answers specific conservation questions on Bosch painting Saint Wilgefortis Triptych

摘要

Raman spectroscopy and time of flight secondary ion mass spectrometry (ToF-SIMS) were used to answer conservation questions left open after the preliminary analysis performed by the restoration team on the Bosch painting Saint Wilgefortis Triptych, within the project "Bosch in Venice." In this work, we present the results obtained by combining these two techniques on five cross sections, concerning a detailed study of pigments and bindings degradation processes, the identification of organic components (binders/lakes), and the characterization of restoration products. Raman measurements show the presence of degradation products, such as calomel on the red pigment cinnabar, calcium-oxalate, in particular weddellite, localized in a not original external layer, and finally lead soaps in several layers of the investigated samples. Although the detection of lead soaps suggests the use of oils as binders, Raman spectroscopy has given no conclusive information about such binders, neither on the possible presence of red lakes, suggested by independent UV observations. Complementary ToF-SIMS investigations have instead revealed the presence of lead palmitate and stearate in the painting layers along with miristic, palmitic, oleic, and stearic acids, thus confirming the use of an oil medium, likely linseed oil. Additionally, ToF-SIMS shows the presence of polydimethylsiloxane, likely from a previous restoration treatment in the 1990s, in the external layer of the investigated cross sections. Due to experimental difficulties during the analysis of the red lake, we can only hypothesize the presence of alizarin.