Shichusen refers to privately produced counterfeit money, as differentiated from the official money coined by the government.
Despite the fact that Kocho-Junisen (12 coins casted in Japan) was the official money during the Nara and Heian periods, shichusen was widely used. During and after the Kamakura period, shichusen of Sung currency was also actively minted, and it reached its peak during the mid to late Muromachi period (it should be noted, however, that imported Sung currency itself was considered equivalent to shichusen, since it was not money issued by the Japanese imperial court, and therefore could not be considered official money). It is known that the imperial court and the Kamakura bakufu (Japanese feudal government headed by a shogun) issued a ban against the use of Sung currency ['Sosen kinshirei']).
The circulation of the extremely poor quality shichusen also led to erizeni (selecting refined coins). In the Edo period, however, as the bakufu enforced its policy on currency by starting to circulate Kanei Tsuho coins, shichusen gradually disappeared.
In order to produce shichusen, a mold is made by using tanesen (the original coin) as the matrix. The quality of shichusen produced greatly depends on the quality of this tanesen. After repeated use of molds, they become damaged, and the impressions on the coins become illegible due to the gradual wear of the impression of the original coin. Molten iron mixed with imported coins was used as the raw material.
In Kamakura, Sakai City, and Hakata, research has been conducted on the lands where the remains of factories of shichusen were found.