We apply Paint on Iron articles to prevent it from corrosion.
Corrosion is a type of Oxidation reaction in everyday life due to which open surfaces of the metals like Iron are slowly eaten away by the reaction of air, water and chemical present in the atmosphere.
Iron articles are Shiny when new, but get coated with reddish brown powder when left for sometime. The process of corrosion of iron items is also called rusting.
Paint does not allow oxygen( from air) and water( moisture) to come in contact with the surface of iron. That is the reason why we apply Paint on Iron articles.