The reason why copper graphite dies are oxidized is that copper is oxidized. Because copper is an active metal element, it is easy to lose electrons and produce oxidation. Or the copper insert is not thoroughly cleaned before silver plating, and there will be black marks on the surface, which is cuprous salt generated after oxidation loses an electron. In addition, due to untimely and incomplete drying after cleaning or poor process, the residual water trace and cleaning solution react electrochemically with copper and oxygen in the air to generate black cuprous, and in severe cases, it is green salt. Or because the silver plating thickness is not enough or the coating falls off, it is oxidized in high temperature environment. Or the insert is stored for a long time and pre-baked for a long time. In addition, atmospheric humidity, surface pollution and impurity gas in the environment will all cause copper oxidation.