Complementary analytical methods for analysis of Ag-plated cultural heritage objects

Abstract

In a preliminary study of American silver-plated cultural heritage objects with the Dallas Museum of Art (DMA), variable plating thickness was observed, which complicates non-destructive characterization of the base metal. Therefore, the objective of this study is to compare the effectiveness of three non-destructive complementary analytical methods to characterize both the plating and the base metal of a typical Ag-plated object and to contrast these results with conventional destructive metallographic methods. An externally purchased 20th century sacrificial Ag-plated “Century” fork was chosen for this study and is similar to one found in the DMA's collection. First conventional destructive metallographic methods, where cross-sections were taken and then characterized using optical microscopy (OM) and scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS), were employed in order to evaluate the effectiveness of the non-destructive methods. The first non-destructive method, synchrotron radiation X-ray diffraction (SR-XRD), reveals the plating thickness, texture related to processing methods, and the phases present in both the base metal and the plating. The second method, dual beam focused ion beam (FIB)/(SEM) equipped with an (EDS) system, provides elemental composition of both the plating and the base metal, as well as imaging of the plating thickness and grain structure, giving some insight into processing methods. The last non-destructive method, handheld X-ray fluorescence (XRF) spectroscopy, provides qualitative elemental compositions of both the plating and the base metal. Each non-destructive analytical method yields complementary results about the composition, plating thickness, texture, and phases present in the plating and base metal of the Ag-plated “Century” fork and aids in the verification of the results from the other methods. Through these methods, we show that successful characterization of Ag-plated cultural heritage objects is possible non-destructively, thus maintaining the object's structural, historical and artistic integrity.