Question

Metals are said to be shiny. Why do metals generally appear to be dull? How can their brightness be restored?

Answer 1

Metals, when exposed to air for a long time, become dull due to the formation of a thin layer of oxides, carbonates or sulphides on their surfaces. This is because they react with various gases present in the atmosphere. This is why metals corrode. But their brightness can be restored by rubbing them with a sand paper. Then the outer corroded layer of the metals is removed and they become shiny again.