Occasionally it is

» necessary to take the temper from a piece of tool steel for forging into another shape, i. e., the steel is to be softened. It is heated to a red heat and is placed between two heavy pieces of pine board. Weighted down, or pressed together in a vise, the steel soon burns a cavity in the wood, and as the two boards come together they completely bury the steel, shuting oil all oxygen and stopping further burning. The charred wood surrounding the steel allows it to cool only very slowly, and in a few hours the metal is cold and soft.

A red hot piece of steel may be softened by burying it in hot sand. The object is slow and even cooling. Some alloy steels cannot be softened by any known means after they are once hardened.