Heat treating metal or glass involves a process called annealing. Annealing is a process of heating and cooling metal or glass to alter its physical and chemical properties. This process can be used to increase the strength and hardness of the material, as well as to improve its ductility and toughness. It can also be used to reduce stress in the material, making it less prone to cracking or breaking. Heat treating metal or glass with annealing can also be used to improve its machinability and formability.