Ketchup! from the following website (and also a recommendation by a maid
service):

http://www.realsimple.com/home-organ...572/index.html

Use ketchup to: Remove tarnish from copper and brass cookware. Squeeze
ketchup onto a cloth and rub it on pots and pans. They should go back to
their coppery color in minutes. Rinse with warm water and dry with a towel.

I don't like ketchup, but like a lot of people I do have a bottle of it. I
had no idea I could use it to clean my copper-clad Revere Ware. Surprise!

Jill