Copper coins are oxidized in the window.

Normal phenomenon. When copper coins are placed in the window, it is easy for water vapor to enter in rainy weather, which causes the coins to be wet and warm, and the ancient coins are corroded and oxidized. Copper coin, an ancient copper token, was originally a round square hole copper coin in Qin State, with the inscription "Half Liang" and a weight of twelve baht (one or two is twenty-four baht), so it is called "Half Liang" copper coin, which is as heavy as its text.