To avoid the formation of scale in reheating metals, i. e,, the waste of the surface by oxidation, the furnace flame should be a reducing and not an oxidizing flame. No risks of oxidation can be taken with high-carbon and alloy steels (usually crucible steels) as any change in the carbon or alloying metal would reduce the quality of the steel. To avoid oxidation, each billet is coated with fire clay, sand and borax, or other harmless, refractory mixture, and placed in the furnace. After removing from the furnace, this mixture is broken off before the billet goes to the rolls or the hammer.