Solid-State NMR and Resonance Raman Studies of Ultramarine Pigments

We report on a study of ultramarine pigments via Colorimetry, resonance Raman, and 27Al, 29Si solid-state NMR spectroscopy. NMR parameters are shown to correlate well with the intensities of Raman signals corresponding to the chromophores S3−. and S2−.. Further, a correlation is established between the colorimetric parameters L* (lightness) and C* (chromaticity) and the paramagnetic shift in NMR spectra for both 27Al and 29Si. The parameter h (hue) appeared not to vary over the range of paramagnetic host concentrations studied. Preliminary results on faded pigments in both acidic and basic media show that the concentration of diamagnetic guest molecules in the sodalite lattice rises, and some of the paramagnetic species are replaced.