Monitoring the environmental degradation of paint dosimeters used to assess risk for fine art paintings on display by XPS

Abstract

Degradation mechanisms due to the effect of environmental pollutants on ingredients used in cultural objects such as fine art paint media have been investigated by surface analysis and other methods. Painters have used proteinaceous materials such as egg tempera and resinous additives, for example triterpenoid mastic, for many centuries. These paint components degrade by different mechanisms under the influence of atmospheric pollutants such as nitrogen dioxide. In this study, thin layers of egg tempera and mastic resin layers on quartz crystal microbalances (QCM) have been exposed to nitrogen dioxide at up to 100 ppm for 6 h. Surface characterization before and after exposure has been undertaken by monochromatized Al Kα XPS. Before exposure, egg tempera possesses a surface rich in proteins and phosphatidyl dicholine which forms part of its lipid structure. Unexposed mastic resin coating is chemically less complex than the egg coating. Exposure of egg tempera to nitrogen dioxide causes a reduction in the surface concentration of phosphatidyl dicholine and an increase in fatty acid components at the surface. Exposure of mastic resin to nitrogen dioxide increases carbonyl/hydroxyl surface concentrations. Shifts in the QCM resonance frequencies are correlated with the hydrocarbon content of the coating for a fixed exposure to nitrogen dioxide. Copyright © 2004 John Wiley & Sons, Ltd.