1 Mon 'Kan'eitsūhō' Iron alloy, blank reverse

Kan'ei Tsūhō coinage was first authorized in 1636 under the Tokugawa shogunate and became the backbone of small-denomination exchange across Japan for over two centuries. The iron-planchet variant emerged in 1739 as copper supplies tightened under shogunal resource management — a deliberate substitution driven by domestic metal policy rather than shortage alone. Iron pieces were struck at multiple han mints operating under shogunal license, producing significant variation in flan quality and surface texture across the production run.

The blank reverse distinguishes this from later issues that carried mint marks or backing authority identifiers. That absence of attribution makes precise mint assignment nearly impossible without die study.