[Ansteorra] a question for metalsmiths

[Michelle Dodd]

How to clean a mixed metal piece?
I have a leather pouch with a decorated metal plate on the flap. I believe it is silver and bronze. It is several years old. The metal developed dark green spots, when I wiped them off it left light spots on the metal. Apparently whatever protective coating that had been on it has worn off. 

Can anyone please tell me how to clean and protect it?

 

Thank you,

Lady Gabriele