Practically all tools are made from a selected grade of steel called crucible steel. For example, one kind of steel makes excellent razor blades, where keenness is demanded, while another is able to resist blows as well to hold a lasting edge. While it is possible to use the same grade of steel for different tools, it is very necessary to vary the treatment of the steel for the different purposes to which the tool will be put.
In making tools, the steel is forged into the desired shape. Care must be taken not to overheat it while it is being worked. After forging, the steel is brought to a good red heat and then plunged into water, to render it hard and brittle. The cutting edge is then rubbed bright with a piece of emery cloth tacked on a piece of wood. After being thoroughly rubbed, the tool is held over a fire and heated slowly. Here it begins to show color - at first a faint yellow, then a tinge of blue. It finally assumes the color possessed by the bar previous to forging.
The operation of reheating, polishing, and allowing the color "to run" is called "drawing." The faint yellow color indicates that the steel has become toughened - that it has lost its hardness or brittleness and become springy.