Anneal

To heat and then cool metal or glass is to toughen or temper it ? to remove internal stresses and make it easier to work when cool. In other words, this heating and slow cooling can strengthen, harden, and reduce brittleness. Mild steel and brass are allowed to cool slowly, while other metals, such as copper, may be quenched in water. Aluminum and glass are annealed by different processes.Also see malleable.