sandpaper rub its cutting edge bright. The heat that remains in the chisel will run to the cutting edge, starting with a yellow color and gradually turning the bright steel to a very dark blue. Then it should be cooled in water. If the chisel, when
Fig. 4- Various Forms of Tongs
put to use, is found to be too hard or soft, repeat the tempering process. If too hard, let the color become more dark as it runs out. If too soft, a little lighter. A little experience will help one to determine the proper color, especially if one brand of steel is used.
In quenching hot steel to be hardened in water, the degree of heat should be no higher than that at which the steel will harden. It must be an