YakiIre (Clay Tempering) Crossed Heart Forge
Process of Clay Tempering a Tanto Blade. Once the steel is shaped as much as possible in its softer state, it is coated with a thin layer of clay along the edge and a thicker layer on the body and spine. During the hardening process, the split second difference in cooling time caused by the clay layer creates two different hardness areas in the same piece of steel.