Abstract
The manifestations of ancient metals’ embrittlement, cracking and fracture, are challenging problems for restorers and conservators, yet the scientific understanding of these problems is limited. In particular, the study and interpretation of fracture surfaces, fractography, is a minor or non-existent consideration for most archaeometallurgical investigations. This paper presents a survey of fractographic analyses, in combination with the more widely used disciplines of microstructural studies, metallography, and chemical analyses for some Old-World copper alloy (bronzes) and high-silver alloy artifacts that have undergone long-term corrosion and embrittlement damage. We show that fractography, as an adjunct to metallography, can improve the interpretation of these types of damage and assist in selecting the best methods for restoration and conservation of the objects made from these alloys.
Highlights
This paper surveys damage, cracking, caused by long-term corrosioninduced embrittlement of ancient copper and silver alloys, as well as long-term, microstructurally induced embrittlement of silver alloys
Metallographic observations on the unetched cross-section of the rod showed no evidence of intergranular corrosion attack, some pitting was visible under the internal corrosion layer
General corrosion ceases but stress corrosion cracking (SCC) is possible for a wide range of environmental water pH, provided that (i) the metal is susceptible to SCC, and (ii) tensile stresses are present in the metal
Summary
This paper surveys damage, cracking, caused by long-term corrosioninduced embrittlement of ancient copper and silver alloys, as well as long-term, microstructurally induced embrittlement of silver alloys. There are (i) excellent books and symposium proceedings with metallographic and chemical analyses for ancient and historic metals, but no fractography [1,2,3,4,5]; and (ii) authoritative publications on research frameworks and guidelines for best practice that do not mention fractography [6,7] This situation is partly because metallography has proven to be a powerful diagnostic technique for ancient objects (artifacts and coins); partly because of a general unfamiliarity with fractography; and because it is difficult to obtain suitable samples that can be broken open to reveal cracking and fracture details.
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