A small, Classical, inlaid plaque (date unspecified) proven by atomic absorption spectroscopy to be of a bronze with unusually high proportion of silver and gold. It is covered with a matte black surface layer, consisting mostly of cuprite, which resembles that appearing on the Japanese shakudo, and which appears to have been artificially induced. The possibility that this was done by a process described by the Alexandrian alchemist Zosimus is discussed, and the hypothesis that the plaque is an example of Pliny's Corinthian bronze is put forward.