No, You Haven't Done Something Wrong: Copper Cookware And Tarnish
Have you recently bought good-quality nonstick cookware that has a copper exterior, only to see the copper turn into a mottled, blackish mess despite your best efforts to wash it well? That doesn't mean it was actually bad-quality cookware, or that you cleaned it incorrectly. All copper that isn't protected by a special coating is going to develop a tarnish, but there are things you can do to help reduce that tarnish so pans remain as bright as possible. Here are some tips to help you keep those pots and pans shiny.
First, About That Coating
It's common for cookware companies to coat copper cookware with a type of lacquer or other protective coating. This coating makes copper look wonderful, but it's not something you can cook with. The heat from cooking will harm the coating and copper, not remove the coating. The manufacturer of the cookware should include instructions for removing that coating, which usually involves some variation of using a commercial remover or boiling in a solution of baking soda and water.
Clean the Pans Frequently
Even if you see only a little tarnish, it's time to clean those pans. Removing tarnish is simple -- all you need to do is mix a food-based acid with salt and rub it onto the copper. For example, you can dip a cut half of a lemon into salt and rub it around the tarnished area, or you can pour lemon juice onto a cloth, dip the cloth in salt, and rub. You can do the same with vinegar and salt instead of lemon juice.
The faster you remove tiny spots of tarnish, the easier it will be to keep the copper cookware looking good. If you aren't going to use the cookware for a while, inspect it weekly and clean off tarnish as it appears. Tarnish is the result of oxygen in the air reacting with the copper on the pan, so even if you never use the pan, if it's exposed to air, it will eventually tarnish. Heat can make the tarnishing worse.
Soap and Rinse After Cleaning
No matter what you use to clean the pan, you have to wash the pan with soap and water immediately after that. If you use a commercial copper cleaner, you have to wash the pan afterward to get rid of residue that isn't safe for cooking. If you use one of the acid-based cleaners, you absolutely must wash it off despite the fact that the ingredients are foods themselves. When oxygen and copper meet, they combine to form copper oxide, the tarnish that you see. But the Exploratorium warns that when salt is added to the mix, another compound begins to form on the copper: malachite.
If you'd like to learn more about protecting copper cookware, contact cookware companies like iPinium USA to see what they recommend for their products specifically. Because copper cookware can contain so many different materials -- the inside of the pan could be stainless steel or have a nonstick coating, for example -- it's best to find out what a company recommends for its own line of cookware.