How to Harden Metal Traditionally

Put on welding gloves, safety glasses, a face shield and heat-resistant clothing.

Heat the metal until it turns red either by putting the metal into a brazing hearth as a whole piece or by using blacksmith's tongs to heat one part at a time. If using tongs for spot hardening, brush the metal in the fire from side to side. The heating time this requires depends on the metal's thickness, but the general rule is to allow it to get to the color of a cherry.

Remove the red hot metal from the brazing hearth. Carefully, with welding gloves, transfer the metal to an iron pot filled with crushed charcoal. This compound is rich in carbon, which binds to the metal and creates a different physical characteristic that makes the metal stronger. Allow the metal to cool in the charcoal until it reaches room temperature.

Remove the metal from the crushed charcoal. There should be no large clumps of charcoal on the metal. The metal should have its original shape, but with the appearance of a fused compound on its surface.

Reheat the metal in the brazing hearth until it is red hot. The charcoal will be completely absorbed into the form of the metal.

Remove the metal from the brazing hearth. Carefully transport it to a large vat of cold water and plunge the piece into the vat completely and without hesitation. Remove the metal from the water and allow to dry. The metal is now case hardened, which means the outer surface is hard, while the inner structure remains more flexible.