Sent to you by Chris Hunter via Google Reader:
Copper cookware is an attractive kitchen accessory, but only if you take good care of it. Surprisingly, you can keep it as shiny as the day you bought it with a mixture of salt and ketchup.
Mac Kohler, founder of Brooklyn Copper Cookware, shared this zany tip.
My go-to recipe for polishing copper is equal parts kosher salt and ketchup. Squeeze out a big glob of ketchup and add salt in equal measure. Spread the solution on the copperware and work it with a soft cotton or hemp cloth-not polyester or synthetics, as that will scratch the surface.
Kohler explains the science behind this trick, and shares a few other tips for maintaining copper in the interview through the source link. If salt and ketchup don't do the job for you, flour and vinegar might, so give them both a try.