One source for pre-atomic steel is WWII ship wrecks (or before), the foundry process post atomic has "problems" with atmospheric cobalt entering the mix. I mention this so anyone reading this can have some idea of what is being discussed. I don't know of any reason why gold or silver would be effected (or for that matter, would not be effected). It is an interesting idea, though. My guess is that cobalt chemically acts like iron, silver and gold do not.