Cast-iron cookware
Because other cookware cleaning techniques like scouring or washing in a dishwasher can remove or damage the seasoning on a bare cast-iron pan, these pans should not be cleaned like most other cookware. Some chefs advocate never cleaning cast-iron pans at all; simply wiping them out after use, or washing them with hot water and a stiff brush. Others advocate washing with mild soap and water, and then re-applying a thin layer of fat or oil. A third approach is to scrub with coarse salt and a paper towel or clean rag.
Copper sheathing
In the late 18th to early 19th century, Sir Humphry Davy performed many experiments to determine how to lessen the corrosion that the seawater caused on unprotected copper sheathing.
To this end he had various thicknesses of copper submerged on the shore and then measured how much the sea water had degraded each one. Sheets of different metals remained in the seawater for four months and then were examined. Two harbour ships were also used in this test, one with an additional zinc band, the other with an iron one. Davy observed, that while the zinc and iron themselves became covered in carbonate that allowed weeds, plant life and insects to attach themselves to the metal, the copper sheets that were connected to cast iron or zinc parts were free of any attached life forms or discoloration.
Unprotected copper would quickly go from a reddish color to a greenish color of corrosion.
When the other metals were mixed with copper in ratios from 1:40 to 1:150, there was no visible sign of corrosion and minimal weight loss. When the ratio was changed to 1:200 and 1:400, there was significant corrosion and weight loss.
Davy therefore advocated cast iron for protecting copper, since it was the cheapest to manufacture, and in his observations malleable iron and zinc seemed to wear down faster.