This is an amazing tip: Flour, salt and vinegar. I just finished cleaning a copper fire pot 40" in diameter that had been sitting in our back yard untouched for nearly 10 years in two hours without rubbing. And I know it can be done faster with what I've learned.
I tried the paste with rubbing, thinking it could take me days; then I noticed that areas where the paste had sat untouched left the copper brighter than where I rubbed. At that point, I simply painted the paste on, watched Jay Leno's monologue, and cleaned off the paste to find the gloppy black and green replaced by copper color. It needs just a final shine, either with Brasso or more of your recipe.
Thanks! Can't wait to show it to my wife, who decided it needed cleaning.