For the best methods of annealing, hardening and tempering steel, see article steel in this volume. Several valuable facts in regard to glass are alsc given under glass.

Copper, brass, German silver and similar metals are hardened by hammering, rolling or wire drawing, and are softened by being heated red hot and plunged in water. Copper, by being alloyed with tin, may be made so hard that cutting instruments may be made of it. This is the old process of hardening copper, which is so often claimed to be one of the lost arts, and which would be very useful if we did not have in steel a material which is far less costly and far better fitted for the making of edge tools.