annealing , process in which glass, metals, and other materials are treated to render them less brittle and more workable. Annealing consists of heating the material and then cooling it very slowly and uniformly; the time and temperatures required in the process are set according to the properties desired. Annealing increases ductility and lessens the possibility of a failure by relieving internal strains. The process, also called hot working, was known to the ancients.