The Fading of Artists' Colorants by Exposure to Atmospheric Nitric Acid

Lynn G. Salmon and Glen R. Cass
Studies in Conservation, 38 (1993) 73--91


Experiments show that atmospheric nitric acid vapor is capable of inducing fading and color shifts in a variety of important artists' colorants. Seventy-nine samples were exposed to 12 ppb and 40 ppb nitric acid in air at 22 degrees C and 50% RH in two back-to-back experiments of 12 weeks duration each. Half (27/52) of the colorants applied to paper tested showed sensitivity to nitric acid and most (22/27) of the Japanese dyed silk cloths showed some reactivity toward HNO3 at the higher concentration. At a concentration of 12 ppb for 12 weeks, the nitric acid dose (concentration times duration of exposure) employed in this study is equivalent to the dose observed inside an unprotected museum in downtown Los Angeles over a 7 year period.

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Article about my work in Caltech On Campus, October, 1990

Another article in Science News of the Week, July 14, 1990: Pigments take thier NOx

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