How Japanese Knives are Made and the Secret to Their Sharpness
Japanese knives (“wa-bōchō”) and Japanese swords (“nihontō”) are made in the same way. The swords of Japan are said to have the very best blades in the world, and likewise you could also say the same of the knives of Japan. Let’s delve into the secrets of these knives, made one by one and filled with the spirit of the blacksmiths who forge them.
The Difference Between Western and Japanese Knives
Left: Western knife (double-beveled); right: wa-bōchō (single-beveled)
The Making of a Japanese Knife
1. Combining the Two Sheets of Metal
The way the iron and steel are combined during creation characterize Japanese knives. Firstly, the iron is heated in a furnace that can reach 1,000 °C, then the steel is placed atop the iron, the metals are reheated, and the smith hammers them together. By combining soft irons with hard steel, the best qualities of both are brought together to form the foundation of a knife that is both hard to break yet keeps an edge.
Iron (softness): makes the knife flexible and less likely to break
Steel (hardness): gives the knife a sharper edge
* The steel contains tamahagane, a type of ore made from iron sand and considered to be the very finest material. Though tamahagane is usually used as a material in Japanese swords, it is also employed to craft the highest class of Japanese knives. Tamahagane made in a tatara (traditional Japanese furnace) is said to be the best in the world. Also, the purest steel in the world is a type of Japanese steel called shirogami hagane (white paper steel).
2. Setting the Shape and Strengthening the Blade
Once the iron and steel are fused together, the smith begins to beat out the blade in earnest, using a tool such as a hammer. This hammering gives the knife its shape even as it crushes the microscopic bubbles of air in the metal, resulting in a stronger blade.
3. Coarse Sharpening
The cutting portion of the knife (i.e., the steel) is roughly sharpened with a whetstone.
This is a necessary part of the hardening process in which the knife is rapidly cooled in oil immediately after being heated in the furnace. Doing this will harden it even further.
By soaking the knife for an hour or so in a liquid like oil at a temperature even lower (150 to 200 °C) than that of the quenching process, this process returns the quench-hardened knife to its original state. Tempering makes the blade softer in order to create an edge that doesn’t chip or nick easily.
6. Fine Sharpening
The very last step in the forging process, it’s this stage that ultimately decides the quality of a knife. The first processing is called hatsuke, where the blade (that is, the steel) portion of the knife is sharpened at a steep angle. Hatsuke involves as thin of a finish as possible, which relates to how sharp the knife will be. Afterwards, the tiny thorn-like flaps left on the blade’s edge from the sharpening process (called “hakaeri”) are themselves sharpened away, thus finishing the knife.
Crafted like this with such painstaking care, Japanese knives are incredibly sharp and are magnificent in design. As a result, they’re able to cut through soft ingredients like raw fish for sashimi without crushing the food’s delicate shape.