4 Mon 'Bunkyūeihō' Bosen, copper alloy, regular script, KŌSEN HAITEIHA

The Bunkyū Eiraku Tsūhō four-mon piece was authorized in 1863 as Japan's monetary system buckled under the twin pressures of forced trade treaties and a massive outflow of gold triggered by the artificially low gold-to-silver ratio the Tokugawa government had maintained domestically. Copper coinage production was expanded at several furnaces simultaneously, and the resulting die variation across issues is considerable. The "Kōsen Haiteiha" designation refers to the specific wave pattern on the reverse — a classification detail that only acquired systematic importance as collectors began differentiating among the numerous die families in the late Meiji period.