EXPOSURE OF ARTISTS' COLORANTS TO PEROXYACETYL NITRATEEDWIN L. WILLIAMS, ERIC GROSJEAN, & DANIEL GROSJEAN
ABSTRACT—Thirty artists' colorants brushed on watercolor paper have been exposed for 3 months to 48 � 15 ppb of the photochemical air pollutant peroxyacetyl nitrate (PAN) in purified air. These exposures were carried out in the dark at ambient temperature (20 � 2�C) and humidity (RH = 45 � 10%). Color changes (L∗a∗b∗ and ΔE) were measured every week using a reflectance color analyzer. Color parameters (x, y, X, Y, Z, L∗, a∗, and b∗) were also calculated from the 380–700 nm spectra—recorded with a reflectance spectro-photometer—of unexposed colorants and of colorants exposed to PAN for 3 months. Regression analysis of the two data sets for colorants and for standard ceramic color tiles indicated that color changes measured by these two methods were in excellent agreement (near-unity slopes, correlation coefficients > 0.99). Exposure to PAN, which may be present in museum air in many areas of the world that are burdened with photochemical air pollution, resulted in little or no color change for all but two (curcumin and basic fuschin) of the colorants tested, including inorganic colorants, alizarin lakes, quinacridones, triphenyl methanes, arylamides, and natural colorants. A brief comparison is made of artists' colorant fading resulting from exposure to several air pollutants including PAN, ozone, nitrogen dioxide, nitric acid, and formaldehyde.
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