Copper, with its distinctive gleaming amber surface and patriotic history, has many uses and benefits. As owners of copper wares and very familiar with its sensitive surface, we turned to an expert on the matter of cleaning and caring for copper: Mac Kohler, founder of Brooklyn Copper Cookware, the sole manufacturer of copper cookware in the United States. According to Kohler, “Natural patinas take years to build up and some chefs have wares that are envy-inducing.” But if you want to get your copper shining again, here are his top tips.
People misunderstand the patina on copper as damage or corrosion, but in fact it’s simply the settling of molecules into a more stable order. The Statue of Liberty was initially sprayed with a vinegar solution in order for it to obtain its verdigris (the green pigment), which actually protects the copper. Once verdigris sets in, the copper will never corrode. The polishing process actually stirs up the molecules into a state of chaos, and the sheen is derived from the prisms of the molecules.
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—no polyester or synthetics, as they will scratch the surface. Buff it out with another natural soft cloth. If you have dark spots on your copper, they’re likely a carbon stain from cooking something starchy, like pasta. (The water has been taken out of the carbohydrates, creating just carbon, which is black.) Carbon and copper bond easily and these spots require a stronger commercial solution. If they don’t come off, they need to be mechanically buffed, essentially breaking off the carbon on the copper surface. I’ve even heard of people using a shoe buffer or an orbital sander with a buffing attachment!
Copper corrodes when exposed to acid, therefore copper cookware is always lined. You would have to ingest an exorbitant amount of copper for it to be dangerous, but it is better to play it safe and get your mugs relined. However, there is an exception when sugar is involved. The sugar from the ginger beer and simple syrup in a Moscow Mule will impede the copper from leaching into the drink. A good way to test the lining on your mugs or any other cookware is to apply a bit of tomato paste to the section of lining that you are concerned about. If it turns green in the morning, you know that the lining has been breached and your cookware will need to be relined.
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