I bought a couple of nice RevereWare copper-bottomed pans at Goodwill. But their bottoms were covered with thick black crud, I guess it was part tarnish & part cooked-on whatever. I figured I could easily clean it off with copper cleaner. In the past I've used Copper Glo http://yhst-55367440605114.stores.yahoo.net/coglopo.html but I couldn't find it sold anywhere any more. I got some Brasso http://www.homesolutionsnews.us/brassopolish/ but it was smelly (ammonia) and didn't cut the crud. Then I read online that I should use something acidic like vinegar, lemon juice, tomato paste, or even catsup, and salt. That has done a lot to remove a lot of the crud, and the newly-revealed copper is shining brightly. But there are still big patches of black crud. What could I do to eliminate all the crud? Just keep scrubbing off a little more each time I use the pans? Live with it? Or is there something you use that really works well?