When it comes to Japanese swords such as the katana, you are likely to encounter a lot of Japanese terminology to describe different parts of the sword. One such term, the niku, is often talked about when it comes to discussions about geometric blade profile, cutting, and durability. Here we take a closer look at the niku and what it really means in terms of choosing the right sword for you.
The Niku Explained
Translated directly, niku means “meat.” When talking about a blade, the niku refers to the shape of the blade surface between the shinogi, or ridge, and the sharp edge. While all blades technically have a niku, the type of niku varies from a more convex curved shape to flat. When you look at the blade, one sporting a true niku, you will notice that the cross-section is thick and bulging, giving a more curved and rounded approach from the middle of the blade to the sharp edge.
But what does this extra “meat” do for the blade in terms of blade performance? Niku helps the blade absorb shock and impact and significantly reduces the risk of chipping or rolling the blade edge, as well as extends the life of a sword as it has more meat to polish away and still retain its durability. This additional “meat” provides more mass to the blade, effectively making it more desirable for cutting hard objects. However, this additional “meat” and wide-angle cutting surface makes the blade less sharp than those with little to no niku.
Terms and Types of Niku
- Hira-niku – Convex curved surface of the hira ji (blade surface between the shinogi (ridge) and the yakiba (hardened surface between the hamon and the ha)) Exaggerated hira-niku is called “clam edge” or hamaguri ba
- Ha-niku (Hamaguri ba) – Niku between the hamon and the ha saki (sharp edge)
- Hira-niku sukunai – In reality, all swords have a niku, but where the niku is flat and the edge is sharp, it is referred to as hira-niku sukunai
- Hira-niku kareru – This is another term for a thin niku, or one lacking “meat”
- Hira-niku tsuku – When the area of the niku is very thick or “full of flat meat,” it is often referred to as hira-niku tsuku. This was the common style in the tachi swords of the Kamakura era.
- Hira Zukuri – This blade type drops the ridge and sports no niku, making it very thin and sharply angled with a very sharp edge.
How Does Niku Affect the Blade Sharpness?
To get an idea of how niku affects sharpness and cutting ability of a blade, let’s first look at the traditional katana with a niku. This blade will have a fairly wide angle that offers support to the cutting edge. When you strike a target, you would approach with a wide angle. The extra steel of the wide angle acts as a shock absorber and provides support to the blade edge, making it more durable and less likely to chip or sustain any other damage, making it ideal for beginners and those cutting hard targets. It is unlikely to sustain damage with an off-angle cut. However, when you run your thumb across the sharp edge, it may not feel as sharp as blades with hira-niku sukanai. However, you will find it will hold its edge longer and allow for more regular polishing without losing durability.
In contrast, a hira-niku sukani blade, with little to no niku, will appear very sharp-angled and the blade edge will feel very sharp to the touch. The edge of these blades is thinner and sharper, but also weaker as there is less behind the edge to offer support. When cutting, achieving the correct angle is much more important as the area that retains support is much smaller, making it more likely for the edge to chip or sustain damage. In the case of a hira zukuri, the edge is even thinner, making it much sharper, but also more fragile when cutting targets. Blades without niku are best used for soft to medium targets or by experienced wielders.
Things to Consider When Looking at Niku Differences
Authentic and historic katanas all sported niku and niku sharpening as a blade was a significant investment and longevity of the blade was a concern – however, many modern katana enthusiasts are now turning to a flatter sharpening edge that is optimized for cleanly slicing tatami during cutting competitions. Whether you choose a sword with niku or not depends on what you intend to do with the blade, what you intend to cut, and what your skill level is as a wielder.
- A blade with a substantial niku will cut, offer more force, is less likely to sustain damage, and is more forgiving for beginners.
- Blades with minimal niku may be easier to cut, but the margin of error is slimer, meaning the risk for damage is higher with a bad cut.
- With blades sporting no niku and extreme sharpness, like the hira zukuri, you can expect to cut thin, soft targets similar to a hot knife going through butter. However, as the target gets thicker, the friction created by a relatively flat blade will create more drag and will make it less efficient for effective cutting against such targets. With hard targets, the edge of a hira zukuri is likely to sustain damage, such as chipping, rolling, or a complete break of the blade.
- In contrast, blades with hira niku, such as hira-niku tsuku may not be as effective cutting soft targets (akin to using a duller knife to perform surgery) but their unique angle helps reduce the surface area of a cut, thus reducing the friction present when cutting thicker targets. In addition, because the edge is reinforced by the niku, the edge is less likely to sustain damage when cutting hard targets.
At Kult of Athena, we offer a wide range of traditional Japanese blades, such as the katana, inspired by traditional swordsmith techniques. Whether you are looking for an authentic style blade to display or looking for an effective sword for Tameshigiri, we have what you are looking for.
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