I am a professional painter and have painted a 12 x18 C&P. I would use a wire brush or sand paper to take off the oxidation. Wiping the metal down with lacquer thinner will take off any oil that might cause the paint not to adhere. Then I would prime with an oil-based primer specifically made for iron and finish with a high gloss oil enamel. I would use a very soft brush made of china bristle and ox hair. If I can help, feel free to call my cell: 314.315.3779