How Japanese knives are made & the secret to their beauty and sharpness

Japanese knives (“wa-bōchō”) and Japanese swords (“nihontō”) are made in the same way. Not without the reason, 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 made by the Japanese craftsmen.
Let’s delve into the secrets of these knives, made one by one and filled with the spirit of the blacksmiths who forge them by following the process step by step.
Note: For those who want some quick visualisation of the whole process, we’ve included an interesting movie at the end of this article. Enjoy!

The Difference Between Western and Japanese Knives

Before we start explaining the process, it’s crucial to know the difference between Western and Japanese knives. We’ve written about it in this article, but the fundamental difference between Western style knives and their Japanese counterparts, is the fact that the Western knife is sharpened on both sides of the blade. They therefore have what is called a symmetrical bevel:

japanese cuttting edgeJapanese style: wa-bōchō (single-beveled)

japanese cutting blade knifeWestern knife: wa-bōchō (double-beveled)

The Making of a Japanese Knife

Step 1. Joining the two sheets of different metal

The way the iron and steel are combined during creation is what makes for so many different Japanese knive types. Firstly, the iron is heated in a furnace that can reach 1000 °C, then the steel is placed atop the iron, the metals are reheated, and the blacksmith 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

japanese cutting blade knife

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. (Our craftsmen also use it).
Tamahagane made in a tatara (traditional Japanese furnace) is considered to be the most valuable and desired in the world. Also, the purest steel in the world is a type of Japanese steel called shirogami hagane (white paper steel).

Step 2. Setting the Shape and Strengthening the Blade

2

Once the iron and steel are merged together, the knife 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, thus resulting in a stronger blade.

Step 3. Coarse Sharpening

The cutting portion of the knife (i.e. the steel) is roughly sharpened with a whetstone.

Step 4. Quenching

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.

Step 5. Tempering

The craftsman then is 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, which 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.

Step 6. Fine sharpening

sharpening grit japanese knife

The very last and probably the most important step in the forging process is knife’s fine sharpening – 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. We just love it!

 

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