NNP

Temper, Tempering.  Strengthening metal for hardness and toughness. Heat treating changes the hardness of metal, softening steel, for example, to cut or recut a die, or hardening and toughing – tempering – steel so dies can be used in a press for striking. Tempering is accomplished by heating the steel dies to a high degree of temperature, then rapid cooling. Modern heat treating furnaces have temperature control; set a gauge and the steel can be heated to a known temperature. Previously temperature was determined in open furnaces by the color of the heated steel, from straw yellow at 450° to very dark blue at 600°. The cooling is accomplished by quenching – plunging the die into water or oil (thus the terms water quenched steel or oil quenched steel). Drawing the temper or simply drawing, is a repeated process of heating and quenching again. Such repeated tempering can achieve a high degree of hardness (this is how sword blades are hardened for example). Testing the hardness is done with a hardness tester (as a Brinnel gauge, among others), by applying a probe to the metal surface to be tested.  See heat treating.

excerpted with permission from

An Encyclopedia of Coin and Medal Technology

For Artists, Makers, Collectors and Curators

COMPILED AND WRITTEN BY D. WAYNE JOHNSON

Roger W. Burdette, Editor