I have a copper mixing bowl that my mom brought me from France several years ago. I took it out of the box and found some greasy tarnish marks. Several articles I found on the Internet recommended using a paste of vinegar and kosher salt to clean the tarnish. This mixture did get rid of most of the tarnish but now the bowl is lined with multi-colored streaks. Since then, I've read a Chowhound thread warning about how using too much acid in a copper bowl can cause harmful amounts of copper to leach out. Have I now ruined my bowl? Is there a cure for the streaks?