The umbrella handle is made of iron and has a long and narrow cylindrical shape. The manufacturing process of umbrella can not be completely closed, and rainwater can easily penetrate along the gap (usually the corrosion hole at the top of umbrella handle or the joint of umbrella handle). Once rainwater permeates, it is difficult to evaporate, and it is easy to oxidize with iron and air in a semi-closed space to form iron oxide and form "rust".