I moved to the coast about 3 years ago and one of my pieces has developed some green spots which is probably bronze disease.
I havent done anything about it yet but this link below tells you the cause and details the various ways it is cured and prevented. The chemical equations show how it behaves like a biological disease and is self sustaining, so long as there is water and oxygen, as is the case with living things. Very interesting
http://en.wikipedia.org/wiki/Bronze_disease