Copper
Authority: Cookware Manufacturer Care Guides & Copper Metallurgy References
Copper cookware needs two-track care: the tin- or stainless-lined interior gets washed gently, since tin is soft and scratches easily, while the exterior copper is polished with an acidic paste like lemon-and-salt or vinegar-and-salt to dissolve tarnish. Bare copper is avoided as a cooking surface because copper leaching into food is a known health hazard.
Wash the Lined Interior Gently
Wash the tin- or stainless-lined cooking surface with warm water and mild soap only. Avoid steel wool or abrasive scouring pads, especially on tin linings -- tin is a soft metal and wears through with aggressive scrubbing.
Polish the Copper Exterior
Make a paste from lemon juice or vinegar and salt, or use a commercial copper polish, and rub it over the exterior in circular motions. The mild acid dissolves the copper oxide and tarnish layer while the salt acts as a gentle abrasive; rinse and dry thoroughly afterward.
Remove Green Patina (Verdigris)
If the exterior develops a blue-green patina from prolonged exposure to moisture and air, treat it the same way as ordinary tarnish, with an acidic polish, since this corrosion product shouldn't be allowed to build up near food-contact edges.
Never Overheat an Empty Tin-Lined Pan
Tin melts at roughly 450°F (232°C), well within range of a hot empty pan left on a burner. Always add food, oil, or liquid before applying high heat to a tin-lined copper pan.
Re-Tin When the Lining Wears Through
Once the tin lining thins enough to show bare copper or the pan stops releasing food cleanly, professional re-tinning restores the lining. This is routine maintenance for tin-lined copper cookware, not a sign the pan needs to be replaced.
Why Copper Cooking Surfaces Are Lined
Copper is prized in cookware for how quickly and evenly it conducts heat, which is why copper-bottomed pans are common even outside all-copper cookware. But bare copper is not considered safe as a direct food-contact surface: copper reacts with acidic ingredients and leaches into food, and chronic copper exposure is linked to liver and kidney damage. A documented historical example is Indian childhood cirrhosis, a fatal liver disease in infants that researchers linked to boiling milk in copper vessels.
Because of this, copper cookware intended for cooking -- rather than for display -- is traditionally lined with a thin layer of tin, and more recently often with stainless steel, on the interior cooking surface. The lining keeps food from contacting bare copper directly while the copper body still provides its fast, even heat conduction from the outside in.
The Chemistry of Copper Tarnish and Patina
Exposed copper reacts with air almost immediately, forming a thin brown-black layer of copper oxide; left alone, this layer is somewhat protective, slowing further reaction with the metal underneath. Over months or years of continued exposure to moisture and air, that oxide can develop further into verdigris, a blue-green basic copper carbonate patina visible on aged copper roofing and statuary, including the Statue of Liberty. Copper also tarnishes on contact with certain sulfur compounds, forming copper sulfide, similar to the tarnish mechanism in silver.
An acidic polish removes these oxidation products the same way it removes brass tarnish: the acid, whether from lemon juice, vinegar, or a commercial polish, dissolves the oxide and carbonate layers, while salt or another mild abrasive helps lift the loosened residue from the surface.