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31-52-245 Micrographs

 

 

Inv. 31-52-245
Bar fragment
A cut from the square end: magnification, 100x
Etchant: for micrograph on left, Klemm’s III; for micrograph on right, Ammonium hydroxide + hydrogen peroxide
(Sn, <0.012%; As, 0.99%; Ni, 0.10%)

Along one edge in particular, beneath a thin layer of corrosion, there appears to be small islands of re-deposited copper that are mixed up with non-metallic corrosion products. The microstructure of the sound metal consists of equiaxed polyhedral grains that, in their twinning and distortion, are indicative of an annealing treatment after a moderate amount of cold-working along the artifact’s length (left micrograph). Small globular inclusions are well dispersed throughout the interior of the metal, with no particular orientation (right micrograph).

Microhardness VHN: 111 ± 7 (n=5)
Very uniform; what data scatter there is (VHN ranging 122 to 102) seems to be a genuine record of variations in grain size within the bar’s body. What microstructural evidence there might have been of deliberate working of the bar’s squared-off sides most likely is now lost to corrosion.