Annealing

the process of softening and toughening metals so that they are less brittle and more readily rolled into sheets or drawn into wires. Annealing is the opposite of tempering. Copper may be annealed by being plunged into cold water when at a white heat. Zinc heats and grows tough and flexible by the very process of being drawn into wire. Most metals are made flexible and tough by heating them until they are soft, and then allowing them to cool slowly, the more slowly the better. A blacksmith desiring to anneal a piece of iron heats it to a white heat, and then thrusts it into a heap of ashes, which conduct heat poorly, to cool off slowly. On the contrary a sudden plunge into a tub of water hardens or tempers a heated plowshare. Skill is required by the blacksmith to sharpen a plowshare and yet avoid the extremes of brittleness and softness. Wrought iron is, of course, annealed iron.