What is the process of softening hardened glass or metal by heating called?

The process of softening hardened glass or metal by heating is known as annealing. This technique involves heating the material to a specific temperature and then allowing it to cool slowly. The purpose of annealing is to relieve internal stresses that may have built up during previous manufacturing processes, such as cutting, shaping, or hardening. By doing so, annealing improves the material's ductility and reduces brittleness, making it less prone to cracking or breaking.

In the context of metalworking and glassmaking, this process is crucial for ensuring the longevity and durability of the final product. In glass making, for example, the annealing process helps to eliminate tension within the glass, ensuring a stronger and more stable structure. This is particularly important for products that must withstand stress during use.

The other processes mentioned—melting, sintering, and quenching—serve different purposes. Melting refers to the complete transition of a solid to a liquid state, which is not the goal when trying to soften materials while retaining their shape. Sintering involves heating a powdered material below its melting point to fuse particles together, which is different from the softening process. Quenching is a rapid cooling technique used to harden materials, particularly metals, and typically follows