A multi-analytical approach to the characterization of natural organic dyestuffs and inorganic substrates present in the 19th-century artistic oil paints manufactured by a French art materials supplier Richard Ainès

Abstract

This paper presents a comprehensive analysis of artistic paints produced in the 19^th century by a French art materials supplier Richard Ainès. Improved mild extraction with hydrofluoric acid enabled the observation of intact organic dyes. Reversed-phase liquid chromatography with diode-array and mass spectrometry detection was utilised for the identification of 35 dyes present in yellow and red paint samples, and in selected plant extracts. The developed analytical method allowed more efficient separation of several isomeric flavonoid and anthraquinone dye components of the paint samples. Persian berries and weld were identified as the dye sources in the yellow paint samples. The red oil paint had been coloured with the madder lake-type plant. Studies of dye extracts of the historical samples show the presence of uncommon dye components (quercetin-O-rhamnoside-glucuronide and rhamnasin-O-rhamnoside-glucoside) that could enhance this identification. The paint samples were additionally analyzed by X-ray fluorescence (XRF) and scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX). Aluminum, Sn, Zn, Ca, Cu, S, Si, and K were detected confirming the presence of aluminium hydrate and tin salts as carriers, as well as chalk, and other components used during the production of these paints. The SEM with the BSE detector images revealed the homogenous texture of finely ground lake pigments.