ADVANCED MATERIALS & PROCESSES | NOVEMBER/DECEMBER 2024 21 that contain SCC damage[19]. These items have different provenances and vary in size and shape. The cauldron has a diameter of 60 cm, the vase stands 9.6 cm tall, the paten has a diameter of 20 cm, and the kaptorga is 4.6 cm in width. Three samples from the cauldron as well as samples from the paten and kaptorga exhibit intergranular SCC; one sample from the cauldron shows transgranular SCC; and three samples However, the authors’ experience with similar edge damage in sheet metal artifacts suggests that this instance was more likely due to ductile tearing during excavation and on-site handling. In other cases, and with the aid of several colleagues, the authors found definite evidence for SCC in ancient silver and bronze alloys, as well as a probable case of SCC in low-carat (13K) gold. The evidence is summarized in this article. Diagnostic methods included visual inspection, metallography, and fractography[17]. In addition, inferences were taken from established examples, both ancient and modern. Visual inspection of cracking patterns, crack arrest, and cracks associated with probable stress concentrations can be diagnostic for SCC. One example is the silver alloy Enkomi cup[18]. The study of this artifact also relied on inference from known SCC failures in ancient silver. A definitive diagnosis would have required sampling, which was not permitted due to the rarity of the cup. Metallography can also provide good evidence for SCC. It tends to be less diagnostic than fractography, but both enable strong evidence gathering. Further, transgranular cracking is more indicative of SCC than intergranular cracking, which occurs in modern alloys due to several causes. Transgranular cracking is fundamentally more interesting because it varies markedly in appearance and topography[12]. It is worth noting that SCC can occur in both homogeneous and duplex phase alloys. SCC IN ANCIENT SILVER Figure 2 shows four ancient high- silver Ag-Cu alloy sheet metal objects Fig. 1 — Sheet silver head of a Parthian lady. Blue circled region was proposed as possible evidence for SCC[15]. Circa 100 BC to 100 AD[16]. Fig. 2 — Ancient high-silver artifacts containing SCC: The cauldron and vase are approximately 2000 years old; the paten and kaptorga are from the 7th and 10th centuries AD, respectively. Fig. 3 — Fractographic examples of (left) intergranular (kaptorga) and (right) transgranular (vase) silver SCC[17,19]. Fig. 4 — Ancient tin-bronze vessel fragments containing SCC: (Left) Baba Jilan 8th century BC and (right) Sangtarashan 8th-7th century BC.
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