The Four Steps
There are two types of traditional Japanese knives: honyaki (made from a single piece of metal) and kasumi (made by fusing together carbon steel and soft iron). Regardless of the knife type, there are four general steps in the knife-making process: forging, edging, handle making and assembly. A different skilled craftsman oversees each part of the process.
Forging, Edging, Handle makeing and Assembly
Blacksmiths are the most important and celebrated craftsmen in the knife making process. In Sakai city, Japan's most important knife-making region, there are only twenty-five active master blacksmiths. They work freelance, each producing a maximum of ten to twelve blades per day.
Using a coal or gas fired forge, the blacksmith heats a rectangle of carbon steel or another alloy to near 900C (1,652F) and begins hammering it into shape. No thermometers are used; the workshop is kept dim so the blacksmith can determine the temperature by the color of the metal's glow. For a kasumi knife, a piece of soft iron is glued to the hot carbon steel using an adhesive compound that is 20 percent sodium, 60 percent boric acid, and 20 percent iron oxide, then the metal is reheated.
The blacksmith hammers near-molten metal about three hundred times by hand to remove its impurities. A mechanical hammer is then used to shape the metal into a rough outline of the blade and the tang, or nakago (the piece of the blade that will be inserted into the knife handle). After that, the metal is trimmed using a mechanical cutter.
While alternating between hammering and heating, the blade will intermittently cool by several hundred degrees. The application of a clay coating at a certain point slows and evens out the changes in temperature, increasing the flexibility of the finished knife. The blade is later quenched in a cool bath of distilled water to ensure hardness.
When the blacksmith is finished, the knife blade is given to a master sharpener to create the edge. Traditional Japanese knives are only sharpened on one side of the blade; there are no fewer than twenty-five steps to the sharpening, which can be grouped into the following.
The blade is attached to a wooden block and ground on a rough wheel to create the proper proportion and angle for the edge. A piece of bamboo and special sand are used to create a smooth blade face. For kasumi knives, the shapener uses a wooden wheel to create decorative hazing or a matte finish. The craftsman buffs and polishes the knife blade on a fabric-covered wheel. Wooden wheels and natural sharpening stones of decreasing coarseness are used to finish the knife edge.
Woodworkers fashion traditional Japanese knife handles from ho wood, a type of magnolia that is light and durable, and that doesn't get slippery when wet. The handle is turned on a wood lathe to form a tapered cylinder.
Some knife-makers prefer a faceted, octagonal shape to a smoother, round-or-ovoid one. For the best knives, collars of water-buffalo horn are attached to the top of the handle, where the blade is inserted. The assembled handles are sanded to smooth the edges and seams for a comfortable grip.
Finally assembly of the blade and the handle occurs at the individual knife companies. Sitting on the floor, assemblers work silently; the various parts of the knives are spread out on blankets. The tang of the blade is heated before being inserted into the handle.
As it cools, the metal will expand, securing blade to handle. Once the blade is inserted into the wood, the handle is pounded with a mallet to settle the tang fully into its base. The alignment of the blade is checked by eye. The knife-maker engraves his brand by hand.