Case Studies:Case study 38
 Early brass in the ancient Near East
Christopher P. Thornton & Christine B. Ehlers
The early brass production in the Near East lacks reliable data in support of the position that the production of pre-1st millennium BC high-zinc copper alloys was part of an informed, deliberate process employed by metalsmiths. The results of analyses conducted on samples from excavated materials provide evidence for earlier and more widespread intentional brass-making than has been available heretofore. The data indicate that high-zinc copper-base alloys were used to fashion artefacts found in mid-2nd millennium BC contexts at the sites of Tepe Yahya and Nuzi.
A brass bracelet fragment was covered by an even yellow-green patina, with one end having been more heavily corroded. X-radiography of this object showed that the modern corrosion surface does not mimic the original shape of the metal, which was of uniform thickness throughout (about 4 mm). A transverse section of the bracelet revealed a large stress fracture in the centre of the object that runs longitudinally through the length of the object. The metal itself, which contains roughly 19.4 weight percent zinc and 0.86 weight percent lead, has a bright golden hue and contains a number of inclusions determined by (electron microprobe analysis) to be zinc sulphide and lead inclusions. Etching with alcoholic ferric chloride and potassium dichromate revealed fairly equiaxed grains containing annealing twins, with smaller grains toward the outer edge and larger grains along the fracture and centre of the object. This, along with the absence of strain lines, indicates the final step in production was an annealing episode. The fact that this object was not work-hardened as a final manufacturing step suggests it was decorative rather than utilitarian, and likely a bracelet.
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Keywords: Near East, Tepe Yahya, Bronze Age, X-radiography, electron microprobe analysis