Heat treating a sword using a water quench is a tense affair as the sword my crack and many hours of work may be lost. This video shows heat treating a wakizashi I made from forge welded cable that was folded several times. The Japanese differential heat treat calls for coating the back of the blade with a clay layer that retards the quench and allows the covered part of the steel to remain softer. The border between harder and softer steel becomes visible as hamon. Although, the heat treating was successful, the blade developed a welding flaw and at this point it looks like 20 hours of work might have been lost.