Why copper needs careful care
Copper is a fairly soft metal, which means copper pots scratch easily. Plus, the chemical reaction between oxygen and copper (oxidation) can cause the shiny, reddish-brown sheen of your cookware to turn black. When copper oxide comes into contact with moisture (even just the moisture in the air), it will eventually form a green-tinted copper carbonate (also called patina or verdigris, it’s what gives the Statue of Liberty its iconic color). The cool part about this patina is that it actually acts as a preservative, protecting—rather than corroding—the copper underneath. It’s this very property that has allowed archaeologists to find copper cookware in great shape even after it’s been buried for thousands of years. If your pots have turned green, it’s possible to remove the oxidized layer to reveal perfectly shiny, food-safe copper, but it’s a lot easier to regularly clean and shine the metal to prevent that from happening. In other words: use your copper and don’t let it collect dust (or oxidize) on a shelf.
How to clean copper pots
The secret to clean copper is ketchup. Seriously. That’s what Sara Dahmen, a professional coppersmith and author of the forthcoming book Copper, Iron, and Clay: A Smith’s Journey, uses to clean her copper cookware. It comes down to science: the oxalic acid in tomatoes makes ketchup an excellent, readily available medium for getting your copper nice and polished, Dahmen says. Any fruits or veggies with high oxalic acid content could work; Dahmen has heard of people using potatoes, but has found they don’t leave as nice of a finish. Here are some of Dahmen’s top tips and supplies for cleaning your copper pots:
Use a soft cotton cloth. Don’t clean copper with a steel wool pad unless you really don’t care about scratches, she warns.Try to get to know your copper. How old is it? Where was it made? What is it lined with? This will all affect how you clean it. Pots are often lined with tin or stainless steel, though older ones may have nickel or no lining at all. And while vintage looks neat, it can come with its own set of issues: “If it’s pure copper, it shines up with minimal elbow grease,” Dahmen says. But the really old stuff may not be pure—refining techniques weren’t as advanced as they are today. That means the metal will react differently to the acids, she explains. “So it’s a little bit of playing because it’s impossible to know the molecular makeup of that old copper.” When simply wiping her copper with ketchup and a soft cloth doesn’t do the trick, Dahmen ups the ante by making a paste out of ketchup, flour, and a little lemon juice. She lets this sit on the pot for a little while (don’t let it dry—it will be hard to remove and won’t result in as smooth a polish) before wiping it away to reveal a dazzling shine.
Rhubarb is another excellent copper cleaner, thanks to its oxalic acid content, Dahmen says. To use this leafy green, she trims it and cooks it down until it’s mushy (about 10 minutes), then spreads it over her copper and lets it sit for about 15 minutes. After that, she wipes it away with a cloth and rinses the copper thoroughly. Just don’t eat the leaves—they’re toxic.Search for “how to clean copper” on the internet, and many results will suggest vinegar. It’s acidic and works well, but Dahmen says it comes with risks. If you don’t wash off all the vinegar or it mixes with some old food on the pot, it can form a superficial verdigris, which is poisonous. Dahmen learned this the hard way after using a copper bowl for a salad with vinaigrette: she didn’t wash it thoroughly, and a little while later discovered it was turning green. Lemon, she says, is less risky.Salt is another popular suggestion for those looking for something abrasive to scrub off stubborn stains, but Dahmen warns that copper will scratch “insanely fast” with regular table salt. “You have to use a really, really, really fine grain of salt and understand you are probably still going to see fine scrapes,” she says. For that reason, she only uses salt when faced with black, baked-on grease, and even then just uses it to spot clean. Baking powder is a gentler alternative.
I gave it a shot
Here is where I admit I’ve always been apprehensive of copper and my ability to care for it. Many years ago, when I was putting together a wedding registry and thinking about my dream cookware, I wanted copper and my father convinced me it wasn’t worth the hassle. Dahmen’s passionate arguments for why we should care as much about what we are cooking on as we do about the quality of the ingredients we use has made me rethink all that. So, I approached a copper pot with an arsenal of pantry products, rolled up my sleeves, and tried out her tips. The pot I used was not brand new, but it was modern and from a reputable cookware store. It did not have any food caked on, but was dull with some spots. My findings? Ketchup does a good, basic job and got the pot shining in just a few minutes. I can totally see how this is an easy everyday solution. Letting a mixture of ketchup and flour sit for 15 minutes got it even shinier. But sprinkling on baking powder and some lemon juice and letting it sit for 10 minutes before wiping away got it the shiniest of all. The pot was, without a doubt, significantly shinier then when I started, but a few dull spots remained, and the perfectionist in me was getting frustrated. I sent a picture to Dahmen, who said, “If you want uber perfect then you do need to look at rhubarb or head into the chemical cleaners.”
What to do if none of that works
As I discovered, there are times when no combination of pantry items will get your copper shining like new. “There might not be things you can remove unless you mechanically remove them,” Dahmen says. In those rare cases—when there’s just hardened, blackened, caked-on stuff—Dahmen will reach for a rotary tool with an abrasive buffer before swapping the attachment for one with softer nylon bristles. Just make sure you know how to safely operate the tool and wear, at minimum, safety glasses, ear protection, and a face mask. Alternately, you can just leave it be (since it’s purely cosmetic) or send it to a professional. And if you’ve scratched your copper, don’t despair. You can buff out light scratches by rubbing hard with some store-bought copper polish, but deeper ones must be removed with a buffing wheel, Dahmen says. Finally, feel free to experiment. Copper pots should be used and enjoyed without fear. “There’s just what you prefer and what your copper seems to react to,” she says. “Short of scratching it really bad with abrasive, there’s no wrong way to do it.”
