Identification of pigments and media from a paint cross-section by direct mass spectrometry and high-resolution imaging mass spectrometric and microspectroscopic techniques.

Comparative studies of direct mass spectrometry and various imaging mass spectrometric and microspectroscopic techniques are being developed for mapping of the chemical composition of pigments and media in paint cross-sections. A study of a multi-layered embedded paint cross-section obtained from a painting by P Caulfield (Interior with a Picture) demonstrates the analytical approach. Imaging SIMS showed the p(EA/MMA) medium distribution in the cross-section. Spot selective laser desorption MS identified the synthetic organic pigments PR170 and PY3. Imaging SEM-EDX provided high-resolution distribution maps of O, S, Cl, Si, Ca, Cd, Zn, Mn, Ti, Ba and Fe which allowed the assignment of inorganic pigments. Maps of iron and cadmium obtained by SIMS matched well with the EDX maps. Reflection microspectroscopy of the coloured layers in the cross-section confirmed several of the pigment identifications.