Raman microscopy study of synthetic cobalt blue spinels used in the field of art

This study aims to provide a better understanding of the Raman spectra of cobalt-based pigments in works of art. Systematic analyses of 21 industrial blue cobalt-based pigments were carried out by using elemental energy dispersive spectroscopy and phase analyses by X-ray diffraction (XRD) and Raman microspectroscopy, which led to the identification of 17 spinel Co-based pigments. All the minerals contained in each pigment were characterised by all three techniques and subsequently attributed to diluents, extenders, mineralisers or unreacted reagents or to the main mineral phase, whether it was pure or contained doping or lattice modifier elements. In the particular case where doping elements were in low concentration in the host mineral lattice, their distinction by XRD from non-doped spinel was impossible. On the contrary, Raman microspectroscopy turned out to be a perfect tool for detecting the presence of the doping agents in the spine! lattice. The determination of the elemental and mineralogical composition of the industrial blue cobalt-based pigments commercially available for artists and studied in this survey represents a significant increase in the amount of analytical data available for this type of pigment as well as a valuable addition in the characterisation by Raman microspectroscopy of these compounds in situ, on works of art. Copyright (C) 2010 John Wiley & Sons, Ltd.