If the coins were just discolored because of dirt, the detergent would wash the dirt away and make them shiny.Because you need to remove a layer of copper oxide, you need to make a strong acid.

• 如果钱币因肮脏而变色，洗洁剂即可将它们洗净并变得闪亮，要去除那层铜氧化物则需强酸帮忙。