The Ozone Fading of Traditional Chinese Plant Dyes

Yun Ye, Lynn G. Salmon, and Glen R. Cass
Journal of the American Institute for Conservation 39 (2000) 245--257

ABSTRACT

Silk samples dyed with 12 traditional Chinese plant dyes were examined to measure their rate of fading upon exposure to atmospheric ozone. Samples of the same colorants extracted directly from the dried plant materials and applied to watercolor paper also were tested for their sensitivity to ozone-induced fading. The samples were exposed in a chamber to an atmosphere containing 0.40 ppm ozone at 25C and 50% RH, in the absense of light, for 22 weeks. Colorant on paper samples produced from the dyes jiang huang (turmeric), zi cao (gromwell), and zi ding cao (violet) proved to be particularly reative toward ozone and faded by ΔE > 10 over the course of the experiment. Ju zi pi (tangerine peel extract) on paper changed color by ΔE > 5, whith an increase in reflectance below a wavelength of 530nm and a decrease above 530nm. All but one of the reamining colorant samples on paper changed by ΔE > 2 as a result of ozone exposure. Color changes observed among the dyed silk samples generally were smaller than for the colorant-on-paper systems, dued to their darker initial depth of shade and hence higher colorant concentration per sample, to their greater saturation of colorant throughout the cloth, and to the effects of mordanting. Colorant-on-silk samples showing color changes of ΔE > 2 over the course of the experiment include zi cao (gromwell), su mu (sappan wood), huang zhi zi (gardenia), jiang huang (turmeric), and zi ding cao (violet).

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