A SPECTROPHOTOMETRIC AND FLUOROMETRIC STUDY OF SOME ANTHRAQUINOID ANDINDIGOID COLORANTS USED IN ARTISTIC PAINTINGS

The present study was undertaken to investigate the potential of spect rophotometric and fluorimetric techniques for identifying the material s used in artistic paintings. Two classes of organic colorants were ex amined, anthraquinoid and indigoid dyes, in their naturally occurring and synthetic forms. Absorption and fluorescence spectra were recorded in both solution and solid layer using linseed oil as a binder. Fluor escence quantum yields were determined. A non-destructive, instrumenta l set-up to record fluorescence spectra on painted surfaces was succes sfully tested. The solvent effects on the spectra of the dyes are inte rpreted in terms of intra-and inter-molecular hydrogen-bonding interac tions. Molecular aggregation of indigo was investigated in dichloroeth ane solution and assigned to a dimer. The spectra recorded from the pa inted surfaces are broader than in solution. However, the emission spe ctra are still suitable to identify the colorants. (C) 1998 Elsevier S cience B.V. All rights reserved.