Ordinary white cast iron can be rendered sufficiently malleable to admit of changes if heated with iron oxide. By this means the carbon in the cast iron is slowly oxidized by the oxygen in the surrounding oxide. The iron should be as free as possible from phosphorus and should contain some manganese. This process produces a layer of pure iron possessing the property of wrought iron. Malleable iron is practically wrought iron which can be hammered into any desired shape when cold, but which is very brittle when hot. Cast iron can be made harder by a chilling process.