Forging a Differential Tempered Katana Blade

Step 1 - Rough Forging

The blade is forged by hot forging a billet of super high carbon steel into the shape seen here. The repeated hammering  provides an even dispersion of carbon throughout the steel for uniform strength of the finished blade

Step 2 - Rough Shaping

The scale is removed and the blade is shaped roughly to the required dimensions. At this stage, the steel is still in the annealed (soft) state and the blade is straight.

Step 3 - Clay Covering

A special clay is applied to the blade by hand, using a thin covering near the edge and a thicker layer over the rest of the blade. This results in a relatively quicker cooling of the edge during quenching, producing a harder cutting edge and a softer back (spine).

Step 4 - Quenching

This is a critical part of the operation. The blade, with its clay covering is heated to a predetermined temperature and quenched in a water bath. The shape and continuity of the hamon, the sori (blade curve) and blade straightness  are all determined by the care and skill exercised in quenching.

Step 5 - Sizing

The sori is adjusted if necessary, to set the point of balance and point of percussion. The blade is the de-scaled. Rough polishing is carried out to size the blade accurately. The habaki is then fitted.

Step 6 - Finishing

Careful final polishing and fine finish work are carried out on the various surfaces to define ridge lines and bring out the beauty of the hamon.