Characterization of Lapis Lazuli Pigments Using a Multitechnique Analytical Approach: Implications for Identification and Geological Provenancing

Many of the Raman spectra obtained from areas painted with ultramarine pigments in illuminated manuscript leaves from the 14th century Italian manuscript the Laudario of Sant'Agnese, in the collection of the J. Paul Getty Museum, also contain strong bands not typically associated with this pigment. The source of these features was investigated using a multitechnique analytical approach. Techniques employed include Raman microspectroscopy, scanning electron microscopy with energy-dispersive spectroscopy, electron probe microanalysis, and laser ablation inductively coupled plasma mass spectrometry. The results indicate the presence of diopside (CaMgSi2O6), a mineral commonly associated with lapis lazuli in nature, and suggest that transition metal dopants in the diopside may be responsible for the Raman features, likely the result of fluorescence with vibronic coupling. The implication of this result with respect to using Raman spectroscopy as a fast, non-invasive, and nondestructive method for determining the geological provenance of natural lapis lazuli pigments used in art is discussed.