A multi-analytical study of early twentieth-century industrially produced cobalt blue paints from Edvard Munch’s studio

Based on the necessity of understanding the dynamics behind the darkening and degradation phenomena of cobalt blue oil paints observed in Edvard Munch's paintings, ten industrially produced cobalt blue oil paint tubes from the artist's studio were investigated. The synergic use of mu -Raman, ATR-FTIR, GC-MS and SEM-EDS techniques led to an overall characterization of the paints. The goal of this research was to further investigate the composition of these industrially produced cobalt blue oil paints and examine their implications in the observed deterioration and darkening phenomena in the blue painted areas in Munch's artworks. Pigments, binding media admixtures and additives present in the manufactured formulations were assessed. The analysed paints were characterized by complex mixtures, featuring the presence of non-drying or semi-drying oils, metal soaps and preservatives. Additionally, extenders, among others clay minerals and white pigments, and adulteration with other blue pigments were identified. The extensive detection of metal soaps in the analysed paint tubes, together with the specific deterioration patterns observed in Munch's paintings investigated, led to some preliminary considerations on the role of these components based on the reported literature.