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Why Ketchup Makes Copper Pots and Old Pennies Shine Again

The condiment aisle hides a real tarnish remover, and simple acid chemistry explains why it works so well.

By Simple Yet Genius Team · · Updated August 4, 2026
Half of a tarnished copper pot gleams again where ketchup has just been wiped away.
Half of a tarnished copper pot gleams again where ketchup has just been wiped away.

The claim has the shape of a prank: smear ketchup on your dull copper pot, wait a few minutes, and wipe away years of tarnish. Then you try it, and the shine follows the sponge. We checked the chemistry behind the trick and found two upgrades that work even faster.

Where this trick comes from

Restaurant kitchens and antique dealers have quietly used the condiment trick for generations, and science teachers keep it alive with the classic dull penny demonstration. It resurfaces online every year because the before and after is dramatic and everyone already owns the cleaner.

What is actually happening

Tarnish is copper oxide, the dull layer that forms wherever copper meets air. Ketchup happens to contain exactly what dissolves it: vinegar. The acetic acid in that vinegar converts copper oxide into copper acetate, a compound that simply wipes away, while the salt in the recipe speeds the reaction along. Classroom chemistry guides explain the salt’s role neatly: it supplies chloride ions that bond with the copper, which frees the acid to keep breaking up more of the oxide layer. Metal restoration guides note that adding salt can strip oxide several times faster than vinegar alone.

Ketchup’s quiet advantage is texture. Straight vinegar runs off a curved pot in seconds, but ketchup clings, holding the acid against the metal for as long as the job takes. The tomato is just the delivery system. The vinegar is the cleaner.

We checked, here is the verdict

Works. This is straightforward acid chemistry, and it performs exactly as advertised on tarnished copper pots and grimy pennies. Want it faster? Mix your own: a paste of vinegar, salt, and a little flour, or half a lemon dipped in salt and used as a scrubber. Both hit harder than the condiment because you control the acid and the salt. Either way the cost rounds to zero, which is hard for any dedicated metal polish on the cleaning aisle to argue with.

Three places to keep the ketchup away: lacquered copper, the shiny display pieces sealed with a clear coating, since acid can blotch the finish; antiques, where collectors prize the dark patina and cleaning can lower the value; and collectible coins, which coin experts say should never be cleaned at all. Everyday pots, pans, and pocket change are fair game.

Try it tonight

  1. Coat the tarnished copper in a thin, even layer of ketchup.
  2. Wait five to ten minutes, or up to half an hour for heavy tarnish.
  3. Rub gently with a soft cloth or sponge and watch the brightness follow your hand.
  4. Rinse thoroughly with warm water so no acid lingers on the metal.
  5. Dry immediately and buff with a soft towel, since water spots invite tarnish right back.

Before and after

Before: a pot bottom so brown it reads as bronze.

After: rosy copper bright enough to check your teeth in.

What people who tried it say

Home cooks in comment threads report the trick working on the first try, usually with some surprise, and parents love the penny version as a kitchen science lesson. The honest notes: decades of built up tarnish can take a second coat or the stronger salt and vinegar paste, and a few users find a dedicated copper polish quicker for big jobs. Nobody disputes that it works.

If you liked this

More pantry chemistry with visible payoffs:

The burger condiment moonlights as metal polish, and the chemistry says it always did.

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