My blades are hand-forged and clay hardened.
In some cases I forge-weld my blades, folding them repeatedly until they contain several thousand layers. In other cases, I start with a bar of modern steel. There are advantages to both construction methods — but by and large I view forge-welded blades as being primarily desirable for aesthetic rather than functional reasons. In simple terms, they look cooler. Forge-welded blades are also closer in construction and appearance to traditional Japanese swords. I also sometimes use self-smelted steel — in Japan this steel would be called tamahagane. Once the steel is smelted, it is forged-welded and folded around fifteen times, producing close to a million layers and leaving an intricate “grain” pattern in the steel.
Once I’ve settled on my steel, I start with a bar of steel which is hand hammered to shape.
This is a two-stage process. First, the bar of steel is tapered – both in length and in width. This is a difficult and time-consuming process. If done wrong, it makes forging the final blade much more difficult…if not impossible. This initial pre-form — known in Japanese as a “sunobe” — sets the overall parameters for the blade.
In the second stage of forging, the bevels are hammered in. In a hira-zukuri blade, that means one set of bevels per side, while in a shinogi-zukuri blade, two bevels are hammered into each side.
The blade is then normalized several times ( a heat-cycling process which refines the grain of the steel, leading to greater toughness and edge-holding ability). After normalizing, I grind off all the scale which has accumulated on the steel during forging and refine the lines of the blade. Much of this work is done by hand with a file. This is a very time consuming process.
Next the spine of the blade is coated with a clay-like material. (Traditionally Japanese smiths use pottery clays, along with various other ingredients such as limestone. I use a refractory cement called Satanite, however, which is more stable than clay.) Once the clay material has dried, I heat the blade to about 1500 degrees Fahrenheit and then plunge it into water. This process yields a blade that is hard on the blade and soft on the spine. The differential hardening process expresses itself in the characteristic hamon (often, erroneously, referred to as a “temper line”).
After hardening, the blade is tempered in a liquid medium (peanut oil, generally) at around 350 to 400 degrees depending on the specific type of steel. This toughens the steel and reduces residual stresses.
The blade is then ground to final shape and polished. I use a combination of modern and traditional polishing techniques. Hand stoning a katana length blade is outlandishly labor intensive. But, particularly with shinogi-zukuri blades, I find that it’s the only way I can make the geometry satisfactory. So I generally do the initial phases of the polishing with Japanese stones, then switch to modern abrasives for the finer polishing. It’s still all hand-work, but the details are slightly different from those used by traditional Japanese polishers. The point of Japanese polishing methods is, above all, to reveal the structure of the steel. Though they are not strictly traditional, the methods I use are more than adequate for revealing the character of the hamon and the hada or grain of the steel.