TL;DR
Tarnish on copper is copper oxide, and mild acid plus salt dissolves it in about a minute. A paste of lemon juice or white vinegar with table salt, worked with a soft cloth and rinsed off immediately, restores the shine on bare copper. Before you start, check whether your piece is lacquered -- polishing lacquered copper ruins the coating.
What tarnish actually is
Copper reacts with oxygen, moisture, and the sulfur compounds in air and food. That reaction produces a thin layer of copper oxide, which reads to the eye as brown, then dark brown, then eventually a green patina.
Nothing is wrong with the metal underneath. The oxide layer is only microns thick, which is why a shine that took years to disappear can come back in minutes.
Acid dissolves that oxide. Salt provides just enough gentle abrasion to break the layer up so the acid can reach it. That is the entire chemistry behind every homemade copper polish recipe.
Check for lacquer before you touch it
Many decorative copper pieces, and some cookware sold for display, carry a clear lacquer coating applied at the factory to stop tarnish. Polish attacks that coating and leaves a blotchy, peeling mess that looks worse than the tarnish did.
Test it by dabbing a small amount of your acid paste on a hidden spot, such as the underside near the handle rivet. Wait thirty seconds and wipe. If the copper brightens, it is bare. If nothing happens at all, it is lacquered.
Lacquered copper gets washed with warm soapy water, rinsed, and dried. That is the whole routine. If the lacquer has already peeled in patches, the only real fix is to strip the coating entirely with a lacquer remover and then treat the piece as bare copper going forward.
What is the fastest way to clean tarnished copper?
Cut a lemon in half, dip the cut face in table salt, and rub the copper in small circles. Alternatively, mix white vinegar, salt, and enough flour to make a paste, spread it on, wait five minutes, and rub off. Rinse thoroughly with warm water and dry immediately with a soft towel.
Working through a heavily tarnished pot
Wash the piece first with warm soapy water to remove grease. Acid cannot reach oxide through a layer of cooking oil.
Apply the paste over the entire outside surface at once so you do not end up with a patchwork of bright and dull areas. Let it sit three to five minutes on stubborn spots.
Rub with a soft cloth or a nonabrasive sponge, following the shape of the pan. Reapply where the tarnish is thickest, usually around the rim and near the handle joints where hands leave salt and oil.
Rinse completely. Leftover acid keeps working and can etch the surface unevenly, and leftover salt accelerates new corrosion. Then dry with a towel right away. Air drying puts water spots on copper faster than on almost any other metal.
Source: metal finishing and conservation care guidance
Protect the lining, because the lining is the fragile part
Cooking copper is almost never bare on the inside. It is lined, usually with tin or stainless steel, because unlined copper reacts with acidic food.
Tin lining. Soft, dull silver-gray, and easy to scratch. Never scour it, never use abrasive powder on it, and never heat an empty tin-lined pan hard, since tin melts at a relatively low temperature and can pool or blister. Wash with a soft sponge and soapy water only. A worn tin lining that shows copper through it should be retinned by a specialist.
Stainless lining. Much tougher. It handles normal washing and a nylon scrubber, and stuck food responds to a soak or the baking soda approach used on burnt sheet pans. Clean stainless with the grain and keep chloride bleach away from it, because chloride pits stainless.
Keep the acid paste on the outside. There is no reason to put it inside the pan, and on tin it does no good.
Keeping copper bright without polishing constantly
Dry the piece the moment it leaves the sink. Water is what starts the next round of tarnish.
Store copper in a dry cabinet rather than hanging over a range, where cooking steam and airborne grease will dull it within weeks. If pieces are decorative and rarely used, a thin coat of a wax made for metal slows tarnishing considerably.
Accept some patina on the parts that touch fire. The area around the bottom of a pan will darken with use no matter what you do, and chasing it with polish every week wears the metal thin over the years.
Never put copper in a dishwasher. Detergent chemistry and prolonged heat discolor copper and can damage a tin lining, the same way it damages cast iron care and dulls nonstick cookware limits.
A safety note on mixing
Stick to one acid at a time, and never combine any acid -- vinegar, lemon juice, a descaler -- with chlorine bleach. That mixture releases chlorine gas. Do not mix hydrogen peroxide and vinegar in a single container either, since the result is corrosive peracetic acid.
Commercial copper polish is fine, but read the label and use it in a ventilated kitchen. Wash the pan with soap and water afterward before cooking in it, and fold that into a full kitchen deep clean so it is not a separate errand.
FAQ
Does ketchup really clean copper?
Yes, and for a reason that has nothing to do with tomatoes specifically. Ketchup contains vinegar and salt, the same two ingredients in a homemade copper paste, held in a thick base that clings to a curved surface. Spread it on, wait a few minutes, rub, rinse well, and dry.
Can I use baking soda on copper?
Baking soda is a mild abrasive and it will remove tarnish with enough rubbing, but it scratches the polished surface over time and leaves a duller finish than an acid paste. Use an acid and salt method instead, and reserve baking soda for stuck food inside a stainless-lined pan.
How do I clean the inside of a copper pan?
It depends on the lining. Tin gets warm soapy water and a soft sponge only, with no abrasives and no scouring. Stainless handles a nylon scrubber and a baking soda paste for stuck food. Never use a copper polish on either lining.
Is it safe to cook in copper that has green patina?
Green patina on the exterior is cosmetic. Green or pitted spots on the cooking surface of an unlined or worn-lined pan should not be used for food, and the pan should be retinned or retired. If you are unsure what your pan is lined with, check with the manufacturer.
Will vinegar damage copper?
Brief contact brightens copper, which is the point. Prolonged contact etches it and leaves an uneven dull finish, so rinse the acid off within a few minutes rather than letting a paste dry on the surface. Always rinse thoroughly and dry immediately.
How often should copper cookware be polished?
Only when you want it to look bright, since polishing is cosmetic rather than functional. Decorative pieces get done a few times a year. Everyday pans can be left to darken, because the copper underneath performs exactly the same whether it is shiny or brown.
The whole-house equivalent of this routine is covered by house cleaning services.
Copper is one of those jobs that is genuinely satisfying by hand, and the rest of the kitchen usually is not. If you want the room around it kept up on a schedule, every home is different, so the real number depends on size, condition, and what you want covered. Get a quote and we will walk you through it.