Moreover, there is a belief that it was difficult to secure a large amount of raw copper for minting coins at the time as the discovery of only one copper mine became a national event; furthermore, there is an opinion that the amount of coins circulated was not much.
また、銅鉱一つ発見されただけで元号を改めるほどの国家的事件と捉えられていた当時において大量の銅原料を確保する事は困難であり、流通量もそれほど多くなかったとの見方もある。