Chemical compositions of ancient coins

Chemical composition of ancient coins may be useful to know the provenance of raw ore materials, technique of minting, route of circulation, and governmental policy or economical conditions of the epoch when they were minted. Thirteen elements (major: Cu, Pb, Sn, Zn, minor: Fe, As, Sb, trace: Co, Mn, Ni, Au, Ag, Se) in Chinese and Japanese ancient coins were determined by inductively coupled plasma-optical emission spectroscopy and instrumental neutron activation analysis. The results show that, in both Chinese and Japanese coins, a transition from Cu-Pb-Sn system to Cu-Zn system occurred in the 15 -- 16 th century in China and in the 18 th century in Japan. Compositional ranges in Cu-Pb-Sn coins extend to 50 -- 80% Cu, 15 -- 35% Pb and 6 -- 15% Sn, respectively, and there seems to be no systematic compositional change with a function of their ages. As to the Cu-Zn coins, the Cu to Zn ratio of Chinese coins is distinctly different from that of Japanese ones, being about unity for Chinese coins and 4 for Japanese ones. In general, Japanese coins are much more abundant in As and Sb than Chinese ones. It is an important problem whether they are impurities of major elements or some components intentionally added in the course of minting. (author)