Kan'ei Tsuho Tetsusen — The Unorthodox Currency Born from Copper Shortage

In 1739, the Edo Shogunate faced a serious issue. The copper coins that had been used as currency since the early Edo period were in short supply due to the depletion of domestic copper mines and the outflow of copper overseas. In particular, in the 4th year of Genbun, the copper shortage became prominent, and the shogunate was forced to make a bold decision to address this. Holding power as the Senior Councilor, Tanuma Okitsugu considered introducing new material to maintain stable currency circulation. Under Tanuma's directive, the shogunate finally decided to proceed with minting round coins with a hole using iron. This decision was one of the innovative attempts in Japanese currency history, as seen in Detailed Explanation of Wado Kaichin. The newly minted Kan'ei Tsuho Tetsusen came in two types, 1-mon coins and 4-mon coins, and circulated at the same face value as copper coins. However, the feel of iron differed from the familiar touch of copper, causing a sense of discomfort among the common people. Nonetheless, the shogunate bet on this new currency system, advancing minting in various domains. Particularly in Mito Domain, Sendai Domain, and Morioka Domain, active production of iron coins took place.

The minting of Kan'ei Tsuho Tetsusen involved many technical challenges. Iron, as a material, was more difficult to process compared to copper, requiring high-temperature handling. This compelled domains to acquire new technological skills. In Mito Domain, experts in minting techniques were invited, and unique furnaces and tools were developed. Similarly, in Morioka Domain, local workers were trained to adapt to new techniques, aiming for efficiency in minting. In Sendai Domain, minting using local iron ore was conducted, promoting technological innovation. In various domains, developing mines to secure the necessary iron for minting was promoted, and the iron supplied from there was transported to minting sites. At these minting sites, temperature management of furnaces was a major challenge, and workers had to exercise utmost caution when working with high-temperature furnaces. Measures to prevent rust on iron were also devised, and the completed coins underwent anti-rust treatment, although this was not a complete solution, and corrosion during circulation remained an unavoidable issue. Despite these efforts, the production of iron coins required more labor and time than anticipated, imposing a greater economic burden compared to traditional copper coins.

When Kan'ei Tsuho Tetsusen was introduced to the market, it was not warmly received among the common people, contrary to expectations. The texture of iron differed from copper, being heavier and feeling different to the touch. This discomfort was particularly strong among merchants and citizens, who still preferred using copper coins. Economically, although iron coins were supposed to circulate at the same face value as copper coins, gaining market trust proved difficult, and differences in actual prices and exchange rates arose in certain areas. For example, while a 1-mon value was maintained in Edo, in rural areas, 4-mon coins were sometimes regarded as having a value of only about 2 mons. This loss of trust led to the rejection of iron coins in many transactions, causing disruptions in currency circulation and adversely affecting economic activities. Types and Identification of Round Coins with a Hole details how these coins were identified and treated in circulation. The shogunate explored additional policies to resolve this issue, but short-term solutions were not found, and iron coins gradually disappeared from the market.

Kan'ei Tsuho Tetsusen existed as part of the Japanese economy from the late 18th century to the mid-19th century, but its circulation gradually decreased. The shogunate sought a new currency system and endeavored to construct a more stable currency regime. Entering the 19th century, as copper supply gradually recovered, the minting of copper coins was again promoted. Consequently, the demand for iron coins declined, and their circulation decreased. Furthermore, by the late Edo period, influenced by the West, new currencies as seen in Value and Identification of Modern Coins were introduced, ending the role of iron coins. Around 1860, iron coins were scarcely seen in the market, and their existence was buried in history. However, Kan'ei Tsuho Tetsusen remains an important document reflecting the economic and political background of the time and is valuable for modern historical research. It provides many lessons for posterity on issues of currency trust and the relationship between material and value. When viewed from the perspective of later generations, the impact left by Kan'ei Tsuho Tetsusen quietly endures in the history of subsequent currencies and collection.