Three decades later: A status report on the silver lacquering program at Winterthur

Bruno Pouliot, Jennifer Mass, Catherine Matsen, William Donnelly, Kaitlin Andrews, and Margaret Bearden

Abstract

Just over 30 years ago, Winterthur began its first museum-wide campaign of cellulose nitrate lacquer application to its collection of historical silver objects displayed predominately in open Period Room settings, i.e. not in display cases. This coating was chosen after testing demonstrated that it could protect the silver from tarnishing for a period of approximately 28 years under regular museum conditions. The lacquering program continues at Winterthur today for about 3,000 silver objects on permanent display in Period Rooms and in the Study Collection. The authors will discuss a project currently underway, which began with a survey of 1,500 lacquered pieces performed to determine the effectiveness of the coating over the years. The results of this survey indicated that the coating had begun to fail on about 42% of the silver pieces. The results were also instrumental in the development of an intensive second campaign of cellulose nitrate lacquering begun in August 2011. As part of this initiative, funded in part by an IMLS grant, 750 silver objects will be re-lacquered, focusing on pieces where the lacquer is oldest or has failed for different reasons. This paper will present the results of many observations made during the project to better understand the behavior of cellulose nitrate coatings on silver objects, its progressive change over time, the instances why it may or may not fail, and the methods used for the removal of old coatings and re-application of new ones. This will include the preliminary results of a study of failed/ discolored coatings via FTIR, tarnish/ corrosion products via Raman, FTIR, XRD, and XPS, and how the presence of lacquer may affect XRF analysis of silver as compared to incipient tarnish. Coating with cellulose nitrate, a material with inherent chemical instability, may at first seem counterintuitive in conservation; to that effect, other preventive methods exist and are successfully in use at Winterthur to retard silver tarnishing.Yet the results of this study demonstrate how effective cellulose nitrate coatings have been within the open environment of Winterthur’s Period Rooms so long as the coating is properly applied, the objects appropriately handled, and with plans and resources in place for the coating’s eventual and “unavoidable” reapplication.

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