Chemical study of the medieval Japanese Mochu-sen (Bronze Coins)

In this paper we have examined the material source of mochu-sen coins, which were minted privately in imitation of Chinese coins during the medieval period in Japan, based on the results of weight and dimension measurement and lead isotope analysis of coins in the Currency Museum of the Bank of Japan. We have also looked at the historical significance of the analytical results and have attempted to make predictions of their implications. The development of mochu-sen coins can be divided into the following three stages from the standpoint of material supply: Stage 1: Coins were made mainly with Chinese lead for example the Shima-sen coins, around the 14th century. Stage 2: Coins were made from both Chinese and Japanese lead for example the Iutsushi-sen coins, made around the 15th century. Stage 3: Coins were basically made with Japanese lead, for example the Kajiki-sen and Kanode Gen’yu coins, in the 16th and-early 17 centuries, though some foreign lead was also used.