Sori, the Curvature of the Japanese Sword Blade


In swords, there is one feature of the shape that is very significant. It is the curvature of the blade. Swordsmiths refer to this as the Sori. What basically is this Sori and what can it do with the sword? More importantly, how does it aid in the actual fight?

We know that the kind of sword matters a lot in the quality of fighting. For instance, the metal composition is very vital. This is what swordsmen are critical about in choosing the right swords. It is because it determines the strength and durability of the blade.

Also, size is an essential factor to consider. It depends upon the user’s motive and fighting style, however. For instance, small swords are more suitable for close-quarter combats. On the other hand, large ones are perfect for open battlefields.

However, little do we realize that even the shape is important. For example, some swords have a certain part wider than the other. Others have it narrower than the rest of the body. As such, the shape may be slender or broad. Smiths have reasons for this variety.

The Sori

Sori is the curvature on the blade of the Samurai sword. Swordsmen sometimes call it the Zori. Also, they often associate it with the Mune, the back part of the blade.

To measure the Sori, first, imagine a straight line between Munemachi and Kissaki. Then, find the deepest point of the curvature. From there, trace a second imaginary line where it intersects with the first one is the point of measurement.

For this, an ideal thickness is usually somewhere between 0.5 to 1 inch. Meanwhile, the maximum one is approximately 1.25 to 1.5 inches.

Source: Wikimedia Commons

What Are Its Types?

Sori differs from sword to sword. For most swords, the difference is noticeable and some have very subtle. Thus, it is sometimes hard to classify. Nevertheless, it is a crucial factor in sword appraisal or Kantei.

Koshi Sori

The term Koshi translates as “waist”. It refers to the deepest point of the curve near the waist of the sword. Particularly, it is just forward of the Machi. To define, Machi is the area where the blade meets the Tang. Simply put, Koshi Sori is between the blade and the Munemachi. However, it is nearer to the Tang than to the Kissaki.

This type of Sori has another name. Certain schools call it the Bizen Sori. This term had its use in history, particularly in the Kamakura Period. For instance, swordsmiths called the late Kamakura swords the Bizen blades.

Torii Sori

This type derives its name from the Torii, the gateway to a Shinto shrine. The reason for such use is its resemblance to the curved crosspiece.

Concerning its location, its deepest point coincides with the middle point of the blade. It is almost perfectly halfway. As such, one can easily pinpoint its difference from the Koshi Sori.

Furthermore, Kyo Sori is another name for this curvature. Kyo, particularly, refers to the Yamashiro Province. Here is where many swords of this form come from.

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Saki Sori

This form takes its name from Saki which means “upper”. As such, the Sori is forward of the halfway point towards the tip or Kissaki.

This form was common during the Muromachi Period. As such, it was evident in most Naginata blades.

Source: Wikimedia Commons

Uchi Sori

Uchi is the inspiration for this form of Sori. It literally means “inner”. As the translation implies, its curve is on the inward portion of the blade. Tanto blade is the best example of swords having this curvature. Meanwhile, people also call this form the Takenoko. In layman’s term, it means “bamboo shoot”.

Mu Sori

Different from all other Sori, this one is straight. For this, the term Mu means “no” or “none”. The Japanese use this to refer to Tanto blades without curvature.

Meanwhile, in the archaic period, Chokuto was what swordsmiths called straight swords. Hence, users sometimes name this type the Chukan Sori. Chukan means “middle”. With this, the deepest point of the curve is between the Sori and Uchisori.

How Important Sori is to the Sword and in Fighting?

Indeed, Sori is as important to the sword as its size, shape, and material composition.

First, it adds to the aesthetics of the sword. It makes the shape look more beautiful. A sword with a curve looks more slender than one without it.

Second, it is easier to draw from the sheath than with a straight blade. As such, it can cut more quickly and efficiently. It does it only in a single motion, in fact. Hence, it can kill multiple enemies.

In connection to this, it captures the sharpness of the sword. Thus, it enhances striking, plunging, and stabbing. The cutting edge must impact the target and inflict damage on it. As such, the sword should be in an angle across it for easier drawing. This angle provides the sword more cutting area than a straight one.

Meanwhile, a straight blade requires intensive training and focus for the user to wield correctly. Its weight does not balance from the top of a galloping horse, for instance. Also, it is likely to get stuck in the target. Hence, there is a possibility of losing it. This is not a problem with a curved sword.

How do Swordsmiths Fashion It?

Smithing the sword with curvature benefits cutting more than thrusting. However, swordsmiths do not intend it to be. They only want to make swords that can cut better. In fact, cutting is the best asset of a sword.

Historically, Rome and other civilizations used bronze. Instead of forging, they made it in a cast mold. Thanks to the advent of steel metallurgy! It opened the doors to new possibilities of sword making and weaponry.

From then on, swordsmiths began using a special type of steel, the Tamahagane. It allowed for forging without breaking and damaging the blade whereas bronze swords were likely to experience this.

People say that the sword gets its distinctive curve through forging. Actually, it obtains it by quenching. In this process, the smith smelts multiple layers of steel sheets. He does it with varying levels of carbon.

He evenly distributes it throughout the blade to eliminate the impurities. When creating the layers, he stretches and folds them. It creates a steel block which he then forms into a billet.

Afterwhich, he places the blade in the forge. He heats the carbon and fuses it with the steel. Then, he quenches the blade in water to cool it. Sometimes, he soaks it in oil. This exposure to such liquids causes the steel to form martensite. This is a body-centered tetragonal form of iron that contains dissolved carbon.

Now, what determines the curve is the rate by which the blade heats and cools. For instance, Katana has its cutting edge thinner than the rest of the body. Thus, that part heats and cools at a different rate.

What is its Historical Background?

Most people think that the Samurai sword has only one specific design. However, it had actually undergone significant changes in shape over time. We call these changes in shape the Sugata. They help in identifying the period the sword originated from. Reasons for such evolution include revisions in battle tactics, types of armor, and fashion.

Heian Era

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This period gave birth to the earliest blades in history. The most recognizable ones were of the Kiriha-Zukuri and Hira-Zukuri types. The former comprised of straight flat swords with chisel-shaped edges and tips.

Meanwhile, the latter consisted of straight flat weapons with curved tips. Some of these had double-edged blades and large ring-shaped pommels. Obviously, these swords had no curves yet. Hence, smiths called these the Chokuto. These weapons functioned mainly as temple swords.

This straight fashion attributed its influence from the Chinese colonizers. They visited Japan via the Korean Peninsula immediately before this period began.

Around 700 to 800 AD, smiths made the Kissaki Moroha-Zukuri Tachi. With a sharpened Kissaki, this had a curved Shinogi-Zukuri blade. This sharp tip extended back about one-third to one-half the length of the Mune.

The most famous of this style was the Kogarasu Maru Tachi. Dubbing this as the Little Crow, smiths made it around 900 AD. This time marked the beginning of the Koto Sword Period.

In the late part of this era, smiths developed the Shinogi-Zukuri Tachi. This had single-edged blade with ridge lines. It measured around 30 inches long. It had Koshi Sori, being near the bottom part of the blade. The blade had a taper or Funbari from the Ha-Machi to the Yokote and Ko-Kissaki.

Kamakura Era

By this period, Tachi became more robust. Particularly, the blades went wider with less taper. This, however, retained small points at the tip. Also, the curvature was less likely to move out to the middle part of the blade. Hence, it was a Torii Sori.

In the middle stage, swords became even stouter with much less taper. They also had short stubby points or Ikubi-Kissaki.

Nanbokucho Era

During this era, blades became flamboyant. They had large wide blades with little curves and large points. Later on, swordsmiths made Hira-Zukuri blades as Chokuto revivals. They also fashioned Nodachi, shouldering swords, with blades having an excess of 50 inches. However, these were too difficult to wield. Hence, swordsmen abandoned them soon.

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Muromachi Era

Muromachi Period
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The early stage of this period resulted in a significant change in the style of blades. It was due to a shift from cavalry to infantry. In turn, this gave birth to the Katana. The first batch of this sword comprised of shortened Tachi. They had the shape of earlier Kamakura blades.

This era was able to preserve this classic Katana until today, which has a length between 27 to 30 inches. Also, it had an average Saki Sori, little Funbari, and Chu-Kissaki.

In the latter part of the period, other changes occurred. For instance, some blades became wider and stouter with slightly larger tips. In fact, these differences were difficult to notice without meticulous blade comparison.

Edo Era

This period brought Japan into 250 years of peace. It marked the end of the Koto Sword Era. At the same time, the Edo-Shinto Period began.

During this time, there had been variations in blade shapes. In particular, blades were in the length of the Katana, being 26 to 29 inches. However, they were stouter. They also had a small curvature and Chu-Kissaki. These were nearly straight, so to say, and were quite robust.

By the middle of the era, sword making gradually declined. It was due to the decreased demand for swords along with the prevailing peace. As such, many of them functioned as swords for entertainment rather than for combat. Their wild, extravagant Hamon and intricate carvings served this purpose well.

It is a fact that for every extreme, there is always a reverse trend. As such, the latter part of the period revived the old Koto styles and methods. Smiths made swords as replicas of the Koto blades. However, they patterned most of them after the shortened Muromachi Tachi.

Meiji Restoration Period

As Japan entered the mid-19th century, the traditional Japanese sword almost ceased to exist. Notably, the Meiji emperor banned the use of swords and abolished the Samurai class. As such, blades after 1876 could no longer consider themselves Samurai swords.

Moreover, most of the weapons in this period departed to the West. These included early English and American collections. Hence, smiths were only able to make a few traditional swords. Many of them were only intended for special occasions. Meanwhile, others were in the Western cavalry fashion. They were mostly factory weapons.

Furthermore, this period covered the Showa Era. During this time, traditional Nihonto evolved into bar-stock, machine-made swords with variations in between. Smiths called these the Showato. They made these to a military standard with blade length between 25 to 28 inches. These swords had only a slight Sori with almost no taper and medium points.

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