Non-invasive detection of lead carboxylates in oil paintings by in situ infrared spectroscopy how far can we go?

This paper demonstrates the efficacy of portable mid-infrared spectroscopy as adiagnostic tool for revealing the presence of lead carboxylates on artworks, in situ,without sampling. Samples of cerussite and hydrocerussite -the main components oflead white- were separately mixed with linseed oil, and artificially aged in two phases.Their compositional changes have been monitored over time by infrared spectroscopyin two investigation modes: absorption (benchtop instrument) and reflection (portableinstrument), and by XRD spectroscopy.Each component of lead white showed different behavior depending on agingconditions, giving important information about the degradation products which arefound in real cases.The accordance of results obtained in both modalities demonstrates that portable FTMIR is a reliable technique for individuating and identifying lead carboxylates directlyon paintings.Examples of the efficacy of this application are provided, by studying paintings from the17th and 18th centuries.