Forging the iron
Kanna (blades) are made from a jigane (a soft iron backing) and a hagane (carbon steel cutting layer).
Jigane are made from materials referred to collectively as kamaji, which include ship boilers and anchor chains, anchors, parts of dismantled iron bridges, railroad tracks (double-head rails), and door bolts. The iron supplied from items manufactured dating from the last part of the 19th century is an essential base metal for crafting soft, easy-to-sharpen kanna.
Jigane are not evenly soft, and cracks in the metal can be repaired to some degree during forging by heating it to just below the melting point. It is difficult to do work this precise by machine, and the bladesmith must keep an eye on the progress to make the necessary adjustments during this process.
The metal is heated in a large forge and stretched to the appropriate width and thickness for the blade being crafted using a large mechanized hammer.
Forge welding and forging
The jigane is forged to the required thickness and width (creating the blade’s base). The jigane is then placed on a hagane layer that has been wetted down and coated with powder adhesive (made primarily of borax). We sometimes use market adhesive powders available on the market, to which we add borax, but we make our own, as well.
The metal is heated to forge welding temperatures, then placed on an anvil and hammered to weld them together (notauchi). Forge welding temperatures vary by type of hagane, which requires the bladesmith to adjust the temperature by sight. While lower temperatures are better for forge welding, metals will not fuse if temperatures are too low. If the temperature is not properly regulated or the metal not precisely hammered, welding defects (cracks, etc.) or blisters (swelling caused by air pockets between the layers of iron and steel) can appear.
The metal is then reheated and hammered out to the desired size (hammering).
Arakenma (Initial grinding)
The head and other parts of the kanna are sharpened and the thickness adjusted in the grinding step. Grinding may not be required if the hammering process has been nearly flawless. However, a blade that is not properly shaped at this stage will cause problems at subsequent stages in the bladesmithing process.
Hizukui and shoton (Smithing and annealing)
The kanna is heated using foot bellows and charcoal, and the ura (back of the blade) is flattened level. The kanna is then heated to a uniform temperature and gradually cooled in straw ash. Allowing the kanna to cool down slowly within a specific temperature range creates a hagane that is soft enough to be worked by hand (filing and scraping).
Only a few smitheries anywhere in Japan still use bellows and sen during this forging step.
Aranarashi, uratogi, and tsuchimeire (Rough flattening, ura scraping, and hammer patterning)
The blade is placed and hammered on an anvil, and the ura is crafted by flattening the metal and correcting any twist. The upper edge of the ura is decorated in a hammered pattern.
Hagane naoshi and namanarashi (Correcting and curving the hagane)
The hagane is ground to uniform thickness, and the ura is given its concavity. The bladesmith focuses intently on ensuring that the forge-weld seam between the iron jigane and the steel hagane will be perfectly straight at the end of the process.
Namatogi and Namanarashi (Polishing and final curving)
The ura is given a final polishing with a whetstone. Finishing the ura in this way is what distinguishes a Chiyozuru kanna from other hand planes. We use a whetstone for this step, but suppliers of this type of stone are no longer in business. We are using our stock on hand as we search for new suitable materials for this polishing step.
Shaping the blade (filing the sides and scraping the surface)
The sides of the blade are filed to the specific measurements needed for the kanna, and the front of the blade is scraped with a two-handled draw knife called sen. The curvature of the surface is calibrated with a sen to correct any distortion caused during quenching. Bladesmiths go by experience and intuition in judging how much calibration is needed.
Doronuri, yakiire and yugamitori (Mud-coating, quenching, and correcting twist)
The bladesmith coats the blade with mud and uses bellows to gradually heat pine charcoal to quenching temperatures. The kanna is then plunged into a tub of water to cool it instantly. Each smithery uses a different type of mud for this process. While some use mud available on the market, Chiyozuru kanna are coated for tempering in a special mud that comes from natural mountain soil. Coating the kanna in mud prevents irregularities caused by quenching and makes for a beautiful kanna surface.
Yakimodoshi and Yugamitori (Second tempering and correcting twist)
Placing the blade in a tub filled with oil toughens the hard quenched hagane for greater durability.
Togi and Meikiri (Polishing and inscribing)
The blade is given a final polishing, and we inscribe our name on the upper edge of the ura. The proper name for this technique is keribori. Each stroke is a deep triangular incision linked with the next stroke to carve out the letters of the inscription.
Craftsmanship
