Take a metal piece and use the gas gun and blow with appropriate pressure so that one can observe the color change. You can see a white layer on the metal. Apply flux on the metal piece and rub it gently so that the small holes are covered. Let it dry for sometime. Start heating the metal gently with high flame for about five minutes. You can see water evaporating out of the flux on the metal. It protects metal from fire scale and will not allow oxygen to stay there. Now turn off the gas gun and rinse the metal.