Fading of artists' pigments due to atmospheric ozone

Recently, it has been shown that several artists' pigments will fade in the absence of light if exposed to atmospheric ozone at the levels found in Los Angeles photochemical smog. In the present study, a large number of artists' organic watercolors have been examined to further assess the scope of this fading hazard to works of art. Twenty-seven organic watercolors were exposed to 0.31 ± 0.12 ppm 0_3 at 46 ± 6% relative humidity for 90 days. It was found that all of the watercolors containing alizarin derived pigments (1, 2-dihydroxyanthraquinone lakes) are susceptible to fading in the presence of ozone. A number of pigment blends containing at least one ozone fugitive chemical component were found to change their apparent color after exposure to ozone. Several organic red pigments that are much more ozone resistant than the alizarin lakes, including quinacridone reds and BON arylamide reds were identified. This information may aid artists in selecting more durable substitutes for the ozone fugitive alizarin lakes.