Behind the Bocour Label: Identification of Pigments and Binders in Historic Bocour Oil and Acrylic Paints

Abstract

A selection of Bocour materials, including Hand Ground Oils, Bocour Artist Oil Colors, Bellini Artists’ Oil Colors, Magna Plastic Artist Paint, Magna Varnish, and Aqua-tec Acrylic Polymer Emulsion paints, dating from the 1940s–1980s was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, and x-ray fluorescence spectroscopy to identify the pigments, fillers/extenders, and media. In several instances, the labeling on the paints was found to be inaccurate, with the color names not corresponding to the pigments present. The labeling often did not indicate the presence of added fillers/extenders, including barium sulfate, which was commonly found in many paints, especially the cadmium red and yellow series. Many of the cadmium paints were found to contain both cadmium sulfoselenide pigments and synthetic organic pigments, suggesting the addition of less expensive colorants. Microfade testing of the cadmium-based red, orange, and yellow paints showed that, despite the presence of added organic colorants, most are as stable as Blue Wool Standard 3 (BWS); however, two samples faded between BWS 2 and 3, suggesting that some paints may be more vulnerable to light exposure than would be commonly anticipated.