As you scroll through pages and pages of different Japanese swords online, the terminology can often be overwhelming. This is especially true for those new to swords. Chances are the term “blade geometry” has popped up a few times, but what does it really mean? What are the different geometric blade profiles common in Japanese swords and what difference does the profile really make? Here we take a closer look at some of the different geometric blade profiles and how they differ in look and performance.
What is the Geometric Blade Profile?
The geometric blade profile, or blade geometry, refers to a combination of things, such as the general shape of the blade, the cross-section shape, the type of edge formation, and how the blade tapers from the base to the tip. In addition, blade geometry can also take other factors into consideration, such as harmonics, nodes within the blade, and more. If you break it down to the basics, the blade geometry simply refers to the blade shape and dimensions.
While you can easily understand terms such as blade length, width, and edge, other terms associated with the blade geometry include:
- Temper Line (Hamon) – this is the visible line that highlights the difference between the soft and harder metals in a differentially tempered blade. For Japanese blades, this temper line is called the Hamon.
- Cross-Section – This refers to the shape of a blade as seen in a cross-section segment of the blade.
- Distal Taper – This taper refers to the change in thickness from the base of the blade to the tip and can affect blade control.
- Curvature – This refers to the forward or backward curve of the blade.
- Tang – This is the section of the blade that is not typically visible, as it is underneath the grip, or handle.
- Center of Balance – this is the point on the blade where it is balanced.
- Center of Percussion – This is a term used for cutting and refers to the “sweet spot” of the blade, or the area where there is little vibration when you strike an object.
What Do the Different Profiles Mean for Cutting?
When you look at the Japanese sword, such as the katana, the physics of cutting is not the same as what you do with your kitchen knives. When it comes to a sword, the blade acts more like a wedge that creates a fracture in the surface of the object you are cutting. Friction between the blade edge and the surface of the cutting object causes the initial tear with a shearing force. Because the main factor that affects the cut is friction, you can find that a dull blade can still achieve a decent cut. However, the sharper the blade edge, the more it concentrates the energy to a smaller area, allowing the sword to generate more friction throughout the cut.
Swords, like the katana, have two cutting planes and it cuts through targets following those planes. The geometry of your sword helps to determine the optimum angle your blade needs to follow for a successful cut. For example, a blade designed for cutting hard targets, such as bamboo or hardwood dowels, will have a thicker profile with a thicker, rounder cutting edge. Blades with a thinner, narrow edge are more designed for soft targets. And swords with an even balance of durability and sharpness work best for tatami. The reason being is the thinner the blade, the less durable it is against hard objects.
Common Japanese Blade Profiles
So now that you have a better understanding of some different blade geometry concepts, let’s look at and compare some of the common Japanese blade profiles and how they differ from each other.
Shinogi Zukuri
The shinogi is a ridge line on a blade that runs from the yokote to the nakago (tang). Blades with this ridgeline are considered Shinogi Zukuri. This is the most common profile found on the katana. When it comes to cutting, there are a few different options for the Shinogi Zukuri, and they focus most on the height of the blade. A high shinogi ridgeline has the most strength and is designed for cutting hard materials, such as bamboo. A low shinogi is designed for soft materials but is very weak against hard materials. A medium shinogi works to cut both soft and hard materials.
When talking about the shinogi, you must also talk about the niku, or meat of the blade. A shinogi zukuri with a niku, which have a rounded and slightly curved cutting edge, giving it a rounder cutting angle. A shinogi zukuri without niku will have a much more straight, thin, and sharp cutting angle.
Hira Zukuri
The hira zukuri profile is most commonly seen in tanto blades and is best designed for soft targets. In contrast to the shinogi, the hira eliminates the shinogi ridge, yokote, and the niku, giving it a very angled point and a razor-sharp edge. Unfortunately, this design makes it very prone to chipping and breaking when used against medium to hard targets.
Shobu Zukuri
The shobu zukuri is similar to the shinogi with the ridgeline, however, the shobu zukuri is missing the yokote and instead has a tip that curves more upward. This profile is commonly seen in the wakizashi swords. The lack of yokote and slight upward curve of the tip is designed to improve tip cutting, however, the tip and blade can be considered less durable than the shinogi zukuri.
Unokubi Zukuri
The Unokubi Zukuri, meaning Cormorant’s neck, and often called the Nagamaki Naoshi is a blade with excellent balance and a strong cutting blade. This blade has a shinogi ridgeline but there is a deep scoop in the last 2/3 of the blade, where there is instead a short bo-hi (groove) with a diagonal termination. This design lightens the blade while keeping the strength and thickness, making this a great cutter without being as heavy as other profiles.
Kissaki-Moroha-Zukuri
The kissaki-moroha-zukari, also known as the Kogarasu Zukuri, is a unique bridge between the old Japanese double-edged ken and the tachi and katana. The blade is a curved, double-edged blade with one side shaped like the traditional tachi. However, unlike the traditional tachi, the tip is symmetrical with both edges of the blade sharp. A koshi-hi groove runs from the tang to the transition point where the blade becomes double-edged and, in traditional swords, there is a straight hamon on both sides of the blade. While rare in production swords today, this style is most famous for the Kogarasu Maru, a blade believed to be created by the famous swordsmith Amakuni in the 8th century.
At Kult of Athena, we strive to offer a wide selection of Japanese swords that sport a variety of different geometric blade profiles inspired by the traditional swordsmith techniques. Browse of selection today to find the blade profile that fits your needs and delivers the sword that is perfect for you.
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