Archaeometallurgy Community:
Dr. Russell Wanhill has shared the following three articles that are of interest to the community.
(1) Wanhill, R.J.H. Case Histories of Ancient Silver Embrittlement.
J Fail. Anal. and Preven. 11, 178–185 (2011).
https://doi.org/10.1007/s11668-010-9429-5
Free to read at: https://rdcu.be/b8PGU
Abstract
This article discusses six cases of ancient silver embrittlement. The diagnostic techniques and results are surveyed, followed by the most likely explanations of embrittlement. There are two basic types of embrittlement: corrosion-induced, and microstructurally induced, which can act synergistically. Corrosion-induced embrittlement takes several forms, including what appears to be intergranular and transgranular stress corrosion cracking. The main intrinsic factor facilitating corrosion-induced embrittlement is retained cold-work in the silver. Microstructural embrittlement is characterized by intergranular fracture, most probably due to low-temperature segregation of lead to the grain boundaries. Knowledge of the details of embrittlement can be essential for optimizing the restoration and conservation of damaged artifacts.
(2) Wanhill, R.J.H. Significance of Discontinuous Precipitation of Copper in Ancient Silver.
Microstruct. Anal. 1, 261–268 (2012).
https://doi.org/10.1007/s13632-012-0041-9
Free to read at: https://rdcu.be/b8PGg
Abstract
Discontinuous precipitation of copper has been held responsible for much of the embrittlement of ancient silver objects. The detailed characteristics of this precipitation have been suggested as possible indicators of an object's age and authenticity. These proposals are considered in the light of metallographic and analytical studies of several embrittled artifacts. These studies indicate that discontinuous precipitation is much less significant for embrittlement than residual stresses due to retained cold-work and externally applied stresses due to burial, and that the precipitation characteristics cannot be used for authentication.
(3) Russell Wanhill (2013) Stress corrosion cracking in ancient silver,
Studies in Conservation, 58:1, 41-49, DOI: 10.1179/2047058412Y.0000000037
PDF available at: https://www.researchgate.net/publication/272310632_Stress_corrosion_cracking_in_ancient_silver
Abstract
Six cases of ancient silver embrittlement by corrosion are discussed with respect to evidence for stress corrosion cracking. Both intergranular and transgranular cracking can occur, depending on whether there is retained cold-work in the silver. The severity of cracking is influenced by a combination of factors, including the amount of cold-work in the silver and the burial environment. The burial environment is important for two reasons. Firstly, the soil weight can induce high stresses, particularly in hollow, thin-walled, and incompletely filled-in artefacts. Secondly, grave burials can result in more aggressive soil environments owing to high salinity from body decomposition.
We look forward to your comments from these informative articles.
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David Vargas
Content Developer | Editor
ASM International
Materials Park OH
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