First produced in 1860, iron 4 mon were shiny when they were first cast.
However, most examples today have become rusty with age. Also, the Japanese citizens
did not like to exchange their copper coins for them, as they did not value iron as highly
as they did copper. These coins often have mintmarks on the back, making them easy to identify.
As with the copper 4 mon, they generally have 11 waves on the back
(some 21 wave examples exist, but these are scarce).