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.

Cleaning Copper with Ketchup and Salt

Equal Parts Ketchup and Salt Make Smudged Copper Shiny.

There are many formulas for polishing copper, with concoctions including lemon juice and ketchup as well as commercially available polishes. In your opinion and experience, what is the best way to clean copper?

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!

Steps for Cleaning Copper

Apply. Rub. Buff. Clean.

I was recently gifted a pair of vintage Moscow Mule mugs with the original Cock and Bull restaurant imprint from the 1940s. I’m so excited to use them, but I notice they are no longer lined with anything. For example, all Brooklyn Copper Cookware is lined with tin. How important are the linings in copper cookware and is it dangerous if I drink out of my mugs in their current state?  

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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16 Comments

  1. Posted March 10, 2013 at 11:35 AM | Permalink

    Very informative, thanks

  2. John Mosca
    Posted March 10, 2013 at 12:52 PM | Permalink

    Does Brooklyn Copper do re-lining? Where are they located? Thank you

  3. Rochelle Bernold
    Posted March 10, 2013 at 9:58 PM | Permalink

    Thanks so much for such an informative piece . I'm off to buy a case of kosher salt and ketchup !

  4. Cass
    Posted March 10, 2013 at 11:55 PM | Permalink

    Hi John,

    Good question. Mac's email is on the Brooklyn Copper website (linked from his name in this article). I'm sure he'd welcome the inquiry! Super nice guy.

    Cheers,

    Cass

  5. Adrian
    Posted March 31, 2013 at 12:47 AM | Permalink

    I'm confused. There are two uses for copper, one is decorative, and one is for cookware. I'm concerned about the cookware.

    There is existing science that proves that bacteria are minimised if you use unlined copper cookware. This means that the copper needs to be exposed. On the other hand, there is some substance to the claim that constantly using unlined copper cookware can lead to copper poisoning or toxicity.

    So, if your copper cookware is lined, then you lose the benefit of the copper, and if it is lined (and you want it that way), then the last thing one wants to do is to clean it with an acid and an abrasive.

    All that aside, this article is contradictory. Why would it be enviable for a chef to have a set of copper cookware that has built up a patina (which is only possible if it is unlined), when the article recommends that one relines your cookware if some ketchup will cause it to turn green?

  6. Jennifer S. Li
    Posted March 31, 2013 at 3:20 AM | Permalink

    Hi Adrian,

    Thanks for your question. To clarify, the enviable patina mentioned is referring to the outside of the cookware vessel. The homemade polish that Mac recommends is also for the outside of copper pieces.

    In terms of choosing lined or unlined copper cookwares, you could certainly cook non-acidic foods (or, as I mentioned above, foods and/or beverages containing sugar) with unlined copper cookware and still reap the anti-bacterial benefits without any toxicity. It is very unlikely to be poisoned from copperware–the amount of exposure required is more than any of us would be exposed to in a lifetime. The tin lining also serves the purpose of ensuring that you can cook any food, acidic or non-acidic, without fear of a bad aftertaste or reaction with the copper.

    I hope this answers your concerns. Please feel free to write in if you have further inquiries!

    ~jennifer

  7. Posted January 24, 2014 at 11:59 PM | Permalink

    Why use ketchup, a made-up product, and waste the ingredients not necessary to the task at hand? Tell us, rather, what the vital ingredient/s in the ketchup might be that have the magical property for cleaning copper. They are surely not the garlic and onion powder. The vinegar, tomato paste and salt??? So, would not vinegar, tomato paste and salt in the correct proportion not work as well? Cleaning copper and brass is the bane of my life. But your article is interesting, especially with regard to the black spot stains, and how to deal with these.

  8. Jennifer S. Li
    Posted January 27, 2014 at 6:45 AM | Permalink

    Hi Carol – You can certainly use tomato paste if you like. Ketchup is often cited as a cleaning ingredient simply because most people conveniently already have a big squeeze bottle of the stuff in their fridge. The most important components are the balance of salt and acid in the vinegar and tomatoes–this is what removes the oxidation. See the below link, which offers some help on how to use tomato sauce to clean copper pans. In any case, you whatever you might have handy in your pantry, whether it be ketchup, tomato paste or sauce! http://www.casasugar.com/How-Clean-Copper-Pot-834

  9. Robby
    Posted September 10, 2014 at 10:35 AM | Permalink

    Are they referring to the patina on the outside of the pans?

  10. Robby
    Posted September 10, 2014 at 10:39 AM | Permalink

    Sorry I should have kept reading before I responded. I was under the impression that the wonderful thing about cooking with copper is that it heats quickly and more evenly. Many pots and pans these days have copper in the bottom between the layers of stainless steel.
    I looked at copper cookware at Williams Sonoma once and I am afraid it is way out of my price range so I have no personal knowledge of aforementioned benefits or qualities.

  11. Pat
    Posted December 12, 2014 at 6:00 PM | Permalink

    if unlined copper is not recommended for mugs, how about the copper pipes we use for tap water every day? I'm confused.

  12. alexredgrave
    Posted December 17, 2014 at 4:30 PM | Permalink

    Hi Pat!

    Acid is the culprit that corrodes copper. Since there is no acid in drinking water, you can use an unlined copper cup if you are only using it for that purpose (many actually tout the benefits of drinking water from an unlined copper cup, as your body will absorb essential minerals). We also passed along your inquiry to Mac Kohler and he sent along this more detailed explanation:

    “Copper oxidation begins well below neutral 3.5 pH, and copper (as well as brass) fixtures used to be checked for evidence of contamination like “canaries in the coal mine.” Any corrosion (“verdigris”) in a spigot opening would indicate low pH, meaning there was something acidic in the water supply. Of course, verdigris is toxic and its sulfites and oxides are water soluble, i.e., would leach into the water stream as well.

    In classic meme-propagation fashion, copper therefore started to get a rap as the toxin in the equation – such that suddenly after centuries of doing so, it’s now suggested that drinking water from copper pipes is dangerous. Copper pipes were used well before public water supplies began to be buffered (or “conditioned”) with a variety of simple trace minerals to “soften” and balance the water as close to neutral pH as possible – and even then copper toxicity was not a problem. In fact, copper's natural anti-microbial properties helped decontaminate pathogens in public water supplies, which used to be a very grave issue.

    Evidence of copper leachate in a water stream is indication of an antecedent problem, namely pH-imbalanced or acid-contaminated water corroding the copper pipes. Clean, pH-balanced water does not corrode copper.

    Two other things are worth noting in this regard. First, before the 1970s, lead was frequently a component of solder used to join plumbing pipes and fixtures in all metals. Lead oxidizes readily in air and water, and in the early decades of indoor plumbing, lead was often found in tap water, especially in multi-story urban housing. Lead solder is no longer legal for plumbing use, but some of the concern for all metal piping, including copper, mistakenly stems from this legacy.

    Finally, low pH also accelerates corrosion of black metal (high-iron) pipes, evident by an initial purge of red-brown (rust) water upon opening a dormant tap. Galvanized (zinc) fixtures are similarly susceptible. Poly-vinyl chloride (PVC) pipes are also degradable by low pH – that leachate is, however, invisible. Given the variety of pipes plumbing in a water district, keeping water supply pH neutral or even slightly base is very important.”

  13. Posted February 18, 2015 at 10:57 PM | Permalink

    Hi there, You’ve done an incredible job. I will definitely digg it and personally recommend to my friends.

    I am sure they will be benefited from this web site.

  14. Posted May 13, 2015 at 6:58 AM | Permalink

    Cleaner for Copper or Brass: Make a paste of vinegar (or lemon juice), salt and corn meal. The corn meal helps make it easier to spread on an item and the vinegar /lemon juice and salt do the work.

    https://www.carpetcleanerscleaning.co.uk/pinner-c

  15. Leyla
    Posted July 12, 2015 at 1:59 PM | Permalink

    Thanks for all the informative comments & suggestions, i am attempting to clean my copper elevator doors But how do i keep it from deoxidizing, and how do i seal it or protect it.
    Thanks,
    LA

  16. Posted July 19, 2015 at 8:00 AM | Permalink

    I'm off to buy a case of kosher salt and ketchup…!!!

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