File:Kan'ei Tsūhō (寛永通寳) Copper-alloy coin - Dr. Luke Roberts 01.png

All old Kan'ei coins made for circulation are made of copper alloy. New Kan'ei coins are mostly made of copper alloy as well. However, in the early 1700's copper mines began running out in Japan and copper became more scarce. It gradually became more expensive to manufacture copper coins than they were worth. One of the responses to this problem included making coins of iron which was cheaper. The government first authorized the manufacture of iron coins in 1739. Copper alloy coins continued to be manufactured but frequently of less weight and lower quality than those of the late 17th century. Eventually copper alloy coins were mainly minted in higher denominations of 4 mon (from 1768) or 100 mon (from 1835). The best that can be said for the iron coins is that they have a primitive beauty. Iron is difficult to cast with the fine features of coins and script. The surfaces of the coins are rough. The characters are often unclear in appearance and the inner and outer coin edges are often unfiled and jagged. Furthermore, the iron coins rust easily. From 1866, just about the time of the collapse of the feudal order and during a time of civil war and high inflation, iron coins of 4 mon denomination were manufactured. A copper alloy coin Hirano Shinden, tiger's tail kan (1739) 23mm wide x .9 mm thick A copper alloy coin Naniwa, fine character (1728) 25mm wide x 1.2mm thick An iron coin Kamedo, small size (1765) 24mm wide x 1mm thick note the old style legs even thugh this is a new Kan'ei coin. This is the single exception to the "legs" rule. An iron coin Ishinomaki, small character, haisen (1768)