We have covered the terminologies on the different parts of the western and Japanese kitchen knives in a previous article. Let’s talk about the blades.
Single Bevel vs. Double Bevel 片刄と諸刄
Modern kitchen knives can be roughly categorized under either Single-bevelled (片刄 Kataba) knives and Double-bevelled (諸刄 Moroba) knives. When you look at the the cross-section of a blade, if both sides are sharpened at a similar angle it is a double-bevelled knife; if one side of the blade is flat or concave, the opposite side is convex, then you are looking at a single-bevelled knife.
Knives used by professionals (eg., Sashimi knives, Deba knives, Usuba knives, Hamokiri knives and etc) are almost all single-bevelled ones. When making a cut, the single-bevelled blade does not cut straight and slightly turns in left (for right-handed knives). This feature makes the cut-out part of the ingredient separates easily from the blade so that cuts can be made quickly. Moreover, it is crucial in Japanese cuisine to display the perfectly sliced cross section of the ingredients; single-bevelled knives, capable of closely slicing through the tissue of the ingredients, are the most fitted for this job.
On the other hand, double-bevelled knives can conveniently make straight cuts and can be used by both left and right-handed cooks. The chef knife/Gyuto and carving knife/Sujikri used by professionals, Nakiri knives used by home cooks are good examples of double-bevelled knives. The Chinese knives specializes in chopping and are usually double-bevelled, too.
Combined blade vs. Full-steel blade 合わせ包丁と全鋼製包丁
A blade is called “combined”/”awase” if it is made of softer iron body with only the very edge made of steel. If the entire blade is made of steel, we call it “full steel” blade.
The combined blade is also called Kasumi (霞/haze). This is because the steel part of the blade is polished to a mirror shine, but the soft iron part looks rather “hazy” in comparison.
The advantages of a combined blade over a full-steel one is its toughness and simplicity to maintain. A combined blade combines the best of a hard steel edge and elastic soft iron body, it creates a sharp and long-lasting cutting edge. Such blade is usually cheaper in price.
The shortcomings of combined blades also exist. For thinner blades, like the ones in Usuba knife or Sashimi knives, after years of continuous use, the hard steel can be pulled by the soft iron, causing the blade edge to warp. Warped blade makes it difficult to sharpen evenly on whetstones, resulting in a less sharp edge.
Full steel blades are usually forged from steel containing 0.9–1.2% carbon content. Different from the combined blades, full steel blades do not show the Kasumi/haze, but instead a wavy line (刃文 Hamon)in the middle of the blade along the blade body. This line separates the part of the blade treated with hardening (closer to the cutting edge) from rest of the blade, which is tempered. This makes the edge of the blade hard and more brittle, the body soft but tough. This process is very close to how the Samurai swords are made, giving such blade its name: “本焼き Hon-yaki”, which refers to the “truly hardened blade”.
Since a full-steel blade does not have to go through the combination process, the end products usually do not deviate much from each other. However, full-steel blades are weaker to shock due to their hardness. If not used properly, a full-steel blade can easily develop chipped edge or even split right into two halves during use.
Hon-yaki blades are often forged from high-end steels which are difficult to harden. The hardening procedure and fix-ups can cost considerable amount of labour and also require good techniques. This all makes Hon-yaki knives twice or thrice more expensive than the ones with combined blades.
Blade finishing 包丁の仕上げ
Kuro-uchi 黒打ちrefers to the blackened oxidized layer formed on the blade during the hardening process. Some knife manufacturer keeps this layer on the blade to shave off labour costs; meanwhile, this layer makes the blade more rust-resistant.
Tsuchi-me 槌目 refers to the hammered marks made on the hira of the blade. Gyuto, Santoku and Nakiri knives often adopts such blade finishing. With such finishing, the blade touches less of the ingredient when making the cuts, resulting in less resistance.
Damascus 墨流し is a popular and more expensive finishing technique. The finishing is almost always done by the steel manufacturer; very few blacksmiths are wiling to manually forge such steel independently.
Other finishing techniques include Kasumi as we have covered earlier and dimples, which are most often seen on western knives.
- 包丁と砥石大全: 包丁と砥石の種類、研ぎの実践を網羅した決定版! 誠文堂新光社 (2014/8/19)
- 包丁と砥石 柴田書店 (1999/10/1)