Microstructures of cast silver-copper alloy archaeological artefacts

Northover, S. M.; Northover, J. P. and Imlach, G. G. (2012). Microstructures of cast silver-copper alloy archaeological artefacts. In: EMC2012 (The 15th European Microscopy Congress), 16-21 Sep 2012, Manchester, UK.

URL: http://www.emc2012.org.uk//documents/Abstracts/Abs...


Cast silver-copper alloys objects form a significant part of the archaeological record from the first millenium BC onwards. Although age hardening of annealed and quenched material has been well studied there has been little study of cast microstructures. This work used a combination of scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and optical microscopy (OM) to explore the range of microstructures in archaeological cast silver and compare them with those in modern cast silver. Modern cast silver showed extensive fine scale precipitation of copper within the grains which was unconnected to the copper-rich phase of the primary eutectic. Ancient cast objects displayed a wide range of microstructures, some very similar to the modern cast silver but some quite different. EBSD allowed interpretation of the microstructure close to some grain boundaries whose detail was obscured by the cast structure in OM and SEM images. Orientation images showed fine-scale interpenetration of the adjoining grains suggesting cellular growth, suggesting that over archaeological time boundary modification may take place in cast as well as wrought and annealed structures.

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