還有,你在評級方面有些弄不清。
你可看看網上toning的意思,正是你所提的氧化
What exactly is coin toning?
Toning is a term that describes the discoloration or light patina that forms on the surface of coins due to oxygen and chemicals in the air acting on the metal. This oxidation can result in a variety and level of toning and also depends on the properties of the metal – silver, gold, copper, nickel, etc.