Microscopic Observations and Ion Beam Analyses of Pigment Distribution in Painting Glazes

Abstract Painting glazes, which are coloured translucent layers used in oil paintings, show evidence of pigment migration upon examination of cross sections with optical microscope and scanning electron microscope (SEM). The present work deals with the use of two complementary accelerator-based analytical techniques, Particle Induced X-ray Emission (PIXE) and Rutherford Back-scattering Spectrometry (RBS), to tentatively reveal such a phenomenon in a non destructive way on experimental glazes. These glazes were prepared by successive addition of layers of emerald green pigment dispersed in a linseed oil medium and having the same pigment content. They were then analysed by PIXE and RBS to provide respectively the bulk elemental composition and the depth distribution on the same spot. It is shown that the pigment concentration at the surface increases with the number of layers up to a saturation value, thus revealing the pigment migration toward the surface.