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Published May 1992 | public
Journal Article

Fading of Organic Artists' Colorants by Atmospheric Nitric Acid: Reaction Products and Mechanisms

Abstract

The reaction products formed upon exposure of selected artists' colorants to gas-phase nitric acid have been identified using chemical ionization mass spectrometry. The two organic colorants that were most nitric acid-fugitive were triphenylmethane derivatives: the chloride cationic dye basic fuchsin yielded the corresponding nitrate salt, and the carbinol pararosaniline yielded the corresponding organic nitrate ester. Both also yielded small amounts of benzophenones. Other colorants studied yielded only small amounts of oxidation (but not nitration) products, i.e., phenols and/or ring-opening products: benzoic acid and hydroxyquinacridone from acridones, isatin and isatoic anhydride from indigo, trihydroxyanthraquinone from alizarin, and phthalic acid from Alizarin Crimson. The corresponding reaction mechanisms are outlined. The results are discussed in terms of possible damage to colorants in museum collections resulting from exposure to atmospheric nitric acid.

Additional Information

© 1992 American Chemical Society. Received for review September 19, 1991. Revised manuscript received January 27, 1992. Accepted January 28, 1992. This work has been supported by a contract from The Getty Conservation Institute, Marina del Rey, CA. We thank Dr. Paul M. Whitmore for carrying out the high-concentration screening tests, and Dr. Dilip K. Sensharma for mass spectrometry analyses carried out at the Department of Chemistry, University of California, Los Angeles. At DGA, Mr. Eric Grosjean and Mr. Edwin L. Williams, II, carried out the liquid-phase tests with triphenylmethane colorants and Ms. Denise Yanez prepared the draft and final versions of the manuscript.

Additional details

Created:
August 20, 2023
Modified:
October 19, 2023