If copper are not stored properly, they may turn green easily, which is we usually called verdigris. Do you know how to remove the verdigris on copper. Here is a tip for you.
Ready some salt and vinegar. First scatter some salt on the area. Then pure some vinegar on top of salt. It may takes you about half an hour to remove them out.
This method is quite useful for removing household copper vessels. Just try it if in need.