Zinc oxide is a white pigment, commonly known as zinc white. Its advantage is that it remains white when encountering H2S gas, because ZnS is also white. During heating, ZnO gradually changes from white and light yellow to lemon yellow. After cooling, the Yellow fades. Using this characteristic, it is mixed into paint or thermometer to make color changing paint or color changing thermometer. Because ZnO has the ability of convergence, it is often used as ointment in medicine, and ZnO can also be used as catalyst.