During the examination of the paint layers of works by Ferdinand Hodler, Cuno Amiet, and their contemporaries, significant signs of reactivity and mobility of reaction products were observed. The appearance of the paintings is compromised by pigment colour change and efflorescence of crystalline and amorphous products. These phenomena are in particular associated with a number of environmentally sensitive 19th century industrial pigments.
Within this project our attention was focused on synthetic ultramarine blue and cadmium yellow pigments developed industrially in the 19th century, when not so carefully controlled processes produced unstable pigments.
The observed pigment degradation processes associated with these pigments were characterised using advanced analytical research techniques on samples collected from paintings. Binding media identification, the characterisation of the distribution of pigments and reaction products, and the preparation of model paintings using historically correct materials and techniques were carried out at SIK-ISEA. Experiments were carried out at MicroXAS (imaging microXRF and XRD) and PHOENIX (microXANES) beamlines at PSI targeting specific questions relating to reaction zones and new phases. Three dimensional insight into the extent of paint reactivity were obtained in experiments at the TOMCAT beamline at PSI.