Quantification of the degradation of paintings due to the deposition of atmospheric aerosols

Abstract

Soiling of cultural heritage due to air pollution is a major challenge for the conservation community and it has motivated scientists to understand the mechanisms that govern the processes of degradation and the effectiveness of potential preventative measures. The relationship between perceptible optical degradation of paintings and cumulative exposure to particulate matter has so far not been well established. This study develops a method for the quantification of optical changes resulting from particulate mass deposition on the surface of realistic paintings simulating prolonged exposure in ambient conditions. For that purpose, a painting was exposed to diesel exhaust emissions simulating exposure equivalent to approximately 5 months in polluted atmospheric conditions. The color changes, assessed by a colorimetric technique, indicated detectable color changes under close observation by the end of the exposure. Similar results were obtained following the exposure of a blank canvas acting as a reference to omit potential color sensitivity to the measured optical changes. The experiments showed that exposing the canvases to levels of moderate ambient pollution results in perceptible color difference in less than a year, through a darkening and yellowing effect indicating the vulnerability of unprotected artwork.