Combined study of the morphology and composition of historical cobalt green pigment: toward a deeper understanding of the pigment synthesis

The synthesis of cobalt green pigments ((Zn1-x–Cox)O) from the 19th century remains unstudied. However, it resulted in pigments with various Co/Zn ratios, that ultimately influenced their optical properties. A multi-technique investigation coupling XRF-CT and scanning 3DXRD is proposed to provide high resolution data on the morphology and composition of historical pigment samples to better understand their synthesis history and its effect on the final optical properties of the pigment particle. More specifically, the enrichment of cobalt inside of the pigment particles can reach very low dimensions or densities, yet have major effect on its visual appearance. Only the high resolution of XRF-CT and s3DXRD make possible to detail the powder heterogeneous composition at the sub-millimetric scale.