A means of fluxing cast iron prior to brazing to promote “tinning,” or precoating. The free graphite in cast iron impedes wetting by the braze material. Surface free graphite can be removed by an oxidizing agent such as potassium chlorate. This is spread on the surface to be brazed just ahead of the braze pool on that part of the base metal which has been heated to a red heat. As soon as the oxidizing agent ceases to foam from the heating, the part is ready to be tinned in the usual manner.