sentences:  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.The term "copper-bottomed" continues to be used to describe a venture, plan or investment that is safe and is certain to be successful.The related "copper-fastened" (and verb form "copperfasten") is used similarly, though with the nuance of "secured, unambiguous", rather than "trustworthy, reliable".