Decay characterization of glassy pigments: an XPS investigation of smalt paint layers

The identification and characterization of a particular pigment in an art object or in a paint layer is an important step in the history of art and technology. Moreover, the understanding of deterioration mechanisms is an essential prerequisite for diagnostics and restoration. In this work we used X-ray photoelectron spectroscopy (XPS) to study pure smalt (cobalt-based blue pigment) and smalt in a tempera media (leather-glue). XPS was used to characterize the pure pigment efficiently and to distinguish it in real paint layers. We also studied smalt in leather-glue samples aged in a climatic chamber to investigate the effects of weathering and pollutant concentration on the deterioration process of this paint system. PACS 81.05.Kf; 81.70.Jb; 82.80.Pv