Forgot to mention this awhile back, I needed a book for something on the classical world and came across this one:
Copper and Bronze in Art: Corrosion, Colorants, Conservation (Getty Trust Publications: Getty Conservation Institute) by David Scott
Although it does not address coins specifically, it gives one a better understanding of the copper and how it deteriorates over time.
Not too big on cleaning coins, for obvious reasons, but this book explains what type of corrosion is on an artifact by coloration, gives the formulas of certain types of corrosion on copper and lots of good info.
To get a feel for the book, I think you can get a preview of this book on Google books, but its kinda pricey if you decide to buy it.