江戸時代後期に制作された小判ならびに銀判の制作技法の検討

抄録

The production processes of old Japanese coins, Genbun-koban, Akita-ginban and Morioka-ginban, were studied. These coins were manufactured by a forging method in the Edo-era. Genbun-koban, manufactured at a gold mint of the Tokugawa shogunate called Kinza, in 1736, is made of Au-Ag alloy and its surface is not flat. The residual stress of this coin is compressive, and the residual stress in the stamped area is higher than that in the flat area. The Iroage method was used to color the coin; it is a thermal treatment, resulting in lows the residual stress is smaller at flat area. Akita-ginban, manufactured in the Akita domain in 1863 is made of pure Ag and its surface is also not flat. There is no residual stress in this coin. This result shows that the thermal treatment of this coin was carried out after processing. Morioka-ginban, manufactured in the Morioka domain in 1868, is made of pure Ag, and its surface is flat. The residual stress of this coin is compressive, and the residual stress in the stamped area is higher than that in the flat area. This result shows that the thermal treatment was not carried out after processing. These coins manufactured in the Edo-era thus had different thermal treatments.