copper stain

例句：

1. 1. The old painting had a copper stain on the wall.
   这面旧画墙上有铜色的污点。
2. 2.The pot was stained with copper from the acid it had been sitting in.
   这个锅被酸性物质染色，是铜的。
3. 3.The stain on his shirt was caused by the acid in the chemical cleaner.
   他衬衫上的污点是由清洁剂中的酸造成的。