Understanding silver hollow wares of the eighteenth and nineteenth centuries: Is there a role for X-ray fluorescence?

Abstract

Open architecture energy dispersive X-ray fluorescence (XRF) has been used extensively for the study of historic silver alloys since 1970. Silver alloy analyses are carried out to address questions about an object's provenance, technology of manufacture, authenticity, and condition. However, the data generated from this surface analysis technique rarely represent the bulk alloy composition. Quantitative analysis of historic silver alloys using XRF non-destructively is challenging due to: the objects’ curved and irregular surfaces (absence of ideal and reproducible geometries); element segregation in copper–silver alloys; limited availability of alloy standards for instrument calibration; post-manufacturing acid treatments that dissolve surface copper from the alloy (pickling); the presence of firescale (copper oxides) or other corrosion/tarnish layers; and surface inhomogeneities introduced by polishing. This study represents an attempt to quantify these sources of error, and, where possible, to provide analytical protocols that can minimize or even eliminate them. Examples are provided using English and American silver hollow wares from the New York Historical Society.

Keywords:

• Quantitative XRF
• Silver
• Silver XRF
• Silver ore
• Silver refining
• Silver–copper alloy
• Silver microstructures
• Pickling
• Polishing
• Corrosion

Acknowledgements

The authors would like to thank Winterthur metals curator Ann Wagner, Dr Bruce Keiser from Bruker AXS, Prof. Aaron Shugar at SUNY College at Buffalo, and Margi Hofer of the New York Historical Society for their valued assistance with this research.