Many chefs consider copper cookware the best because it conducts heat evenly and it will change temperature rapidly as a cook turns a burner up or down. But with these benefits come some drawbacks. One of the biggest is that you cannot cook directly on the copper because it is toxic. Many pieces of copper cookware are covered in a thin layer of tin that wears out over time. Retinning copper pots and pans is possible, but it is also dangerous because it requires working with acids and melted metal.
Clean the inside of the pot to remove grease and carbon deposits. Wearing heavy rubber gloves, place the pot in a solution of 10 per cent sulphuric acid and distilled water. It needs about 20 minutes in the bath to remove all of the oxides. Rinse and dry.
Apply a layer of flux to the inside of the pot, which will bind the new tin to the copper.
Heat the pot to 231 degrees Celsius, which is tin's melting point. At this point the flux will be smoking but should not burn.
Wearing heavy leather gloves, put the tin in the pot. As it begins to melt, swirl it around so the tin covers the pot. Alternately, the tin can be premelted in a tinner's pot and poured into the hot copper pot.
Wipe the pot with a heavy cotton cloth that is soaked in flux until the tin is smooth and shiny. This is often the hardest part of the process and probably won't be perfect on a first attempt.
To preserve the tin, never use a metal utensil while cooking and never heat the pot empty.
You will be working with melted metal and acid; take all necessary steps to protect yourself and those who may be around you.