EXPOSURE OF ARTISTS' COLORANTS TO SULFUR DIOXIDEEDWIN L. WILLIAMS, ERIC GROSJEAN, & DANIEL GROSJEAN
ABSTRACT—Thirty-four artists' colorants brushed on watercolor or cellulose paper have been exposed for 12 weeks to 93 � 5 parts per billion (ppb) of the air pollutant sulfur dioxide (SO2) in purified air. These exposures were carried out in the dark at ambient temperature and humidity. 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 spectrophotometer, of unexposed colorants and of colorants exposed to SO2. Color changes measured by these two methods were in excellent agreement for both unexposed and SO2-exposed colorants (near-unity slopes, correlation coefficients >0.9).Exposure to sulfur dioxide resulted in little or no color change except for one category of colorants, the triphenylmethanes basic fuchsin, brilliant green, and pararosaniline base. A second exposure to higher levels of SO2 (920 � 30 ppb) for 2 weeks resulted in little additional color change, if any. A comparison is made of artists' colorant fading resulting from exposure to several air pollutants, including sulfur dioxide, ozone, nitrogen dioxide, nitric acid, formaldehyde, and peroxyacetyl nitrate. Implications for colorant-containing objects in museum collections are briefly discussed.
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