5 CONCLUSION

THE OZONE-INDUCED fading rate of a number of traditional natural organic colorants applied on paper has been examined. Samples were exposed in an environmental chamber to an atmospheric ozone dose equivalent to approximately six to eight years of residence in a conventional air-conditioned building in Los Angeles. Previous studies of the ozone sensitivity of modern synthetic artists' pigments showed that a large number of these materials were relatively stable towards an ozone dose of the magnitude employed here. By contrast, almost all of the traditional natural colorants tested in this work showed some degree of fading after exposure to ozone. This procedure was successful in identifying many natural colorant/paper systems which should be considered ozone-fugitive, and a few (curcumin, dragon's blood, madder lake, and indigo) which are very ozonesensitive. While these results are strictly applicable only to other similar colorant systems (such as watercolors or pastel drawings), at present this study should nevertheless be useful as a guide in the judgment of those natural colorants which, in other applications, warrant particular observation or precautions.

ACKNOWLEDGEMENTS

THIS RESEARCH WAS PERFORMED under a contract with the Getty Conservation Institute, and this article is based on a paper presented at the 14th Annual Meeting of the American Institute for Conservation in Chicago, Illinois, 21-25 May 1986. Natural colorants were made available with the cooperation of Eugene Farrell and Richard Newman of the Harvard University Art Museums, and Gary Wade Alden, of the Balboa Art Conservation Center. The Munsell conversion calculations were performed using a computer program supplied by Max Saltzman and Dr. Fred Billmeyer. Discussions with Mr. Saltzman were helpful in the spectroscopic analyses of the pigments. The authors also wish to acknowledge the assistance of Dr. Helmut Schweppe, whose advice and reference materials aided the thin layer chromatographic identification of the natural colorants.