A Study on the Human Ability To Detect Soot Deposition onto Works of Art

Abstract

Works of art can become soiled due to the deposition of airborne black soot particles within museums and art galleries. The soot particle deposition rates are already known for many environments, but knowing the levels of carbon particle coverage at which humans can detect image darkening is also important. Therefore, in this work, human subjects have been tested to determine their ability to detect soiling by black carbon particles deposited onto specially prepared samples having colored backgrounds. The results show that certain observers are able to detect that a sample is becoming soiled once surface coverage by black carbon particles has reached 2.4% if the soiled samples and clean samples are placed directly adjacent to each other, producing a sharp dividing line (an "edge-to-edge" comparison). Observers can detect the presence of soiling with greater than 90% accuracy during an edge-to-edge comparison on most backgrounds when soiling levels reach approximately 3.6% surface coverage by black particles. If the comparison between soiled and clean samples must be made with samples that are separated from each other by a neutral gray area, soiling is only detected with 100% accuracy once coverage by black particles has reached 12.0% surface coverage. These results show that a greater accumulation of black carbon than was previously thought is required to produce a visibly soiled surface.

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