Although ideal for delicate sauces and foods, whose temperature must be carefully controlled, copper cookware also comes with a great deal of responsibility and maintenance. As the cookware's tin coating wears off over time, the underlying copper can destroy the vitamins and folic acid in the food, and could even lead to the ingestion of toxic levels of copper itself.
Immerse the cookware in a distilled water solution of 10 percent sulfuric acid. Let sit until the copper turns a shade of pink. Then, remove the cookware with copper or plastic tongs.
Scrub the surface with the clean felt pad and pumice. Rinse with distilled water and a clean brush.
Flux the cookware with rosin or tallow. Pre-melt pure tin in a tinner's pot, and pre-heat your cookware to the melting point of tin (450 F). The flux will smoke, but don't worry: it should not burn.
Pour some of the molten tin into the cookware. With a clear cotton rag that has been saturated with flux, quickly wipe the tin around the surface of the copper.
Dump out excess tin, and wipe the surface again with the fluxed rag. The copper and tin will slowly cool, until the tin fully sets. Repeat as needed until the entire surface has been tinned. Patches that don't set can be easily removed with steel wool.