also , even if there had been enough demand , the volume of copper production had been absolutely small , which made it impossible , from the beginning , to supply sufficient copper coins and substitute material money then-current in japan (copper was so precious then in japan that its era was renamed ' wado (literally , japanese copper ), ' upon discovery of copper ore mines , and , as described afterward , the quality of copper coins had rapidly deteriorated as time went on .) また、仮に需要があったとしてもそもそも銅の生産量が絶対的に少なかった当時の日本では実物貨幣に代わるだけの銅銭の製造は始めから困難であった（銅鉱の発見を機に元号を「和銅」と改めてしまう程当時銅は貴重であり、また後述のように時代が下るにつれて急速に品質が悪化している）。
