I have a beautiful copper kitchen sink. when asked if I wanted it polished, I said NO, I like to watch it oxidize, change colors, etc. Well, last night I was making a tomato sandwich, and cut the top off the tomato. It fell into the sink, flat side down. I left it there til this morning. When I picked it up, the copper was shiny! Shaped like the tomato slice! I feel this warrants further research, and possible experimentation with other tomato products; I have a can of tomato juice sitting around. I will not experiment on the kitchen sink, however.

It makes sense. Tomatos are acidic, like lemons. I use salt and lemon juice to shine up my copper bowls.