Pigment analysis of portrait miniatures using Raman microscopy

Abstract

Raman microscopy was used for the in situ identification of pigments and covers of a glazed portrait miniature of Elizabeth I, namely the Armada Jewel, otherwise called the Heneage Jewel. It was confirmed that the gemstones on the frame are diamonds and rubies from their characteristic Raman and fluorescence spectra, respectively. The domed cover on the front of the locket was identified as α-quartz crystal from its Raman spectrum, whereas the flat cover on the reverse side is an amorphous glass. The Raman spectra of the pigments were collected in situ by focusing the incident laser light through the amorphous glass cover. Nine different pigments were unambiguously identified: white lead, vermilion, red lead, azurite, lazurite, orpiment, pararealgar, yellow ochre and malachite. The Raman spectrum of a further, unidentified green pigment exhibits a band of medium intensity at 969 cm −1 and weaker bands at 596, 546, 476 and 388 cm −1. It was shown that this pigment is not chrysocolla, atacamite or pseudo-malachite by comparison of their Raman spectra. Finally, the brown pigment used as a dark tone contains amorphous carbon. Copyright © 1999 John Wiley & Sons, Ltd.