Evaluation of three protective coatings for indoor silver objects

Chandra L. Reedy, Richard A. Corbett, Deborah L. Long, Robert F. Tatnall, and Bradley D. Krantz


Three coatings commonly used for protection of silver artifacts housed indoors (Agateen, Paraloid B-72, and Paraloid B-48N) were tested to rank their performance. Protocols were developed to be relevant to conservation practice, while also incorporating industry testing techniques. A variety of test specimens were used to check for effects of complex geometry and sterling versus fine silver, and to measure changes occurring on the silver beneath the coatings as well as changes of the coatings themselves. Accelerated aging included exposure to fluctuating temperature and relative humidity, and to a variety of common pollutants (hydrogen sulfide, sulfur dioxide, ozone, formaldehyde, and acetic acid). Both visual ranking and quantitative tests were used; data were analyzed for statistical significance by one-way and two-way analysis of variance. Our results show that Agateen protects silver from hydrogen sulfide, even after great environmental stress (i.e., accelerated aging), whereas the two acrylic coatings offer no protection. All three coatings begin to crack and peel slightly after accelerated aging. For the bent specimens with more complex geometry, brushing provides better protection, as otherwise the coatings tend to peel away from edges. For protection against hydrogen sulfide, spraying was sometimes more effective, perhaps because it may result in a slightly thicker and more even coating. Our findings correspond with our field observations and the reported experiences of many conservators. Conservators are sometimes reluctant to use Agateen due to problems with other cellulose nitrate lacquers and to the severe degradation any cellulose nitrate can endure if exposed to very high temperatures or to direct sunlight. However, given the preferred application and appearance qualities of Agateen, our results support its continued use for coating of silver for indoor environments.

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1999 | St. Louis | Volume 6