The New Student's Reference Work/Annealing
Anneal'ing, the process of tempering certain metals and glass to increase their tenacity and render them less brittle by cooling them slowly after they have been submitted to a high temperature of heat. Badly annealed glass, it is well known, will break with a sudden change of temperature, and to obviate this glass vessels are annealed in trays in a long oven, one end of which is hotter than the other—the process of annealing being to draw the trays slowly into cooler and cooler portions of the oven. Cast iron is similarly annealed for tinning; while steel and other metals are tempered after much the same process is undergone. The annealing of the softer metals is done by immersion in boiling water, which is then slowly cooled.