We aplly paint on iron articles in order to prevent it from rusting or corrosion. Painting on iron gate will prevent corrosion by sheilding the metal surface from oxygen and moisture. The other nethods of preventing corrosion are oiling,greasing, Galvanizing,Chromeoplating (or) making alloys. CORROSION: WHEN A METAL IS ATTACKED BY SUBSTANCES AROUND IT SUCH MOISTURE , OXYGEN , ACIDS etc. IT IS SAID TO BE CORRODE ( Rusting ) AND THIS PROCESSVIS CALLED CORROSION.