Medieval bronze objects and coins of the Northern Song Dynasty from the viewpoint of lead isotope analysis

Abstract

There is a theory that in the Middle Ages of Japan, there was not enough technology to mine bronze raw materials in Japan, so coins of the Northern Song Dynasty, which had been imported in large quantities from China, were used as raw materials and recast to make bronze objects. On the other hand, there are some doubts that it was not necessary to recast the currency that had been used and replaced them with other objects. In order to verify that, we selected particularly high-quality large coins from the Northern Song Dynasty which were not in circulation in Japan at that time, performed lead isotope ratio analysis, and compared the results with the data of the previously reported bronze cylinders containing sutras. The reason for choosing large coins was that it was difficult to determine the authenticity of the so many imitation coins made in posterity which remains in Japan. As a result of the analysis, while the previously reported bronze cylinders were within a relatively cohesive numerical range, the coins showed large variations. From this, it was found that coins of the Northern Song Dynasty was unlikely the raw materials of bronze cylinders.