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Suitable Swords for Iai and Test-Cutting
by
Nakamura Taiazburo, Hanshi, 10 dan
(translated by Guy H. Power)
NOTES: In the measurements given, 1 shaku is roughly equivalent to 1 foot. 10 bu = 1 sun (about 1 inch); 10 sun = 1 shaku. Also text in parentheses are notes by the translator.)
LENGTH
(Note: A sword length is measured in a straight line from the munemachi to the kissaki. Regardless of how straight a sword is or how deeply curved it is, the straight line distance is its length.)Sword blades transitioned to 2 shaku 3 sun (about 70 centimeters) because the Tokugawa government (ca. 1600-1867) standardized the measurement. Examples of swords being 2 shaku, and 2 shaku 5 sun exist; however, these were instances where a person's body height was extremely different from the average of the day. Also, the former Imperial Army and Navy military swords were standardized at 2 shaku 2 sun (about 67 centimeters).
Swords used in modern iaido range from 2 shaku 3 sun to 2 shaku 5 sun (about 70 cm. to 76 cm.) in length. Anything longer than that would be for an exceptionally large person. Using a sword longer than 2 shaku 5 sun for tameshigiri (test-cutting) is inadvisable because the body of the blade may be a bit weak due to the excessive length of the blade. The blade may bend or break when combined with the physical shock of striking an immovable object, incorrect blade angle, and an incorrect striking angle. The longer a blade is, the more likely it is to be weak.
I had the considerable opportunity to meet the great master Nakayama Hakudo (Hiromichi) sensei and was able to hear his insight about the length of a sword. Nakayama sensei said that subtracting 3 shaku (90 cm) from one's own height was a good rule-of-thumb; the resulting difference would be a good sword length. From my height of 5 shaku 4 sun (164 cm), I subtracted 3 shaku. Therefore, a good length for my sword would be 2 shaku 4 sun (73 cm). However, this length would only be good for practicing iai kata in empty space; it is just a bit too long for test-cutting. After World War Two I was presented with a koto sword which was 2 shaku 4 sun 5 bu (74 cm) in length and I used it for about five years. But once while test-cutting, my grip was not on the mark and I ended up bending the sword beyond repair.
The standard blade length for modern test-cutting is 2 shaku 3 sun 5 bu (71 cm); I recommend that students do not use swords exceeding this length.
WEIGHT
A regular sword which is good to use will weigh from 1.1 kilograms up to 1.3 kg, including the handle and tsuba. If the sword is any heavier, the practitioner will have to use physical strength. It may appear all right while practicing iaido forms, but when cutting forcefully downward or executing chiburi (blood removal), the blade will often shake uncontrollably when brought to a halt. The root cause of many bad habits in swordsmanship is that the sword is too heavy. It is essential to use caution with a heavy sword.SORI (CURVATURE)
(The sori is measured at the deepest portion between the imaginary " length"-line and the back of the blade.)A sori of 5 bu (1.5 cm) is adequate for a sword of 2 shaku 3 sun (70 cm). Anything deeper or shallower is unsatisfactory for high class swordsmanship.
MIHABA (BLADE WIDTH)
The ideal blade width will be approximately 1 sun (3 cm) at the tsuba-moto (base of the hand guard), and about 8 bu (1.4 cm) at the monouchi ("sweet spot," about 1/3 of the blade measured from the point). The balance of a sword of these measurements will be good. As with the sori, anything more or anything less will be unsatisfactory for high class swordsmanship.NAKAGO LENGTH
The length of the nakago (tang) affects the balance of the sword; this becomes very important for the principles of high class swordsmanship.Generally speaking, koto and shinto swords will have a nakago of approximately 5 sun (15 cm). The standard handle length is 8 sun (24 cm). In this case, if the nakago is too short when cutting through material, the handle can break where the butt of the nakago meets the handle [fig. 5]. If the handle is 8 sun, the nakago should be 7 sun. If you sufficiently place a long nakago in the handle, the balance of the sword will be in the handle. Moreover, in the opposite case, if the blade-weight is light, a short nakago will improve the balance of the sword.
In the case of a heavy blade having a short nakago, the balance can be corrected by placing lead inside the body of the handle near the pommel. The blade will feel lighter because the center of gravity was shifted.
HAMON DEPTH
A hamon (temper line) depth of one-third to one-fourth of the blade width is adequate. When the hamon is gaudily too deep, the blade is generally brittle and will chip easily; also, the blade will break easily. Worse yet, when the blade is hard, its kireaji (ability to cut well) will not be very favorable.MENUKI PLACEMENT
Wrapping the menuki to the handle came about during the Muromachi period (1338-1573) when the fittings were generally in the handachi (half-tachi) style. (That is, although the sword was worn as a katana thrust through a sash with the cutting edge skyward, its fittings and hardware were tachi-style.)The previous Imperial Army and Navy military swords were also outfitted in the handachi style, and the menuki were placed where the palms of the hand meet the handle. During the Edo period (1600-1867) the menuki were placed opposite that of the handachi, on the opposite side of the palm.
The menuki are the overall ornament for the handle; essentially, they are useless when placed in the Edo style. However, if the menuki are affixed in the handachi style, one's swordsmanship will become satisfactory.
90% of the swords used by today's iaido enthusiasts have the Edo style menuki placement.
GROOVE
A sword with a groove will make a whistling sound when swung. Many high- ranking practitioners dislike swords with grooves; however, there are some high-ranking practitioners that like the groove. In the samurai period movies and plays, a whistling sound is dubbed in to appeal to the audience. Also, the novice believes that making the whistling sound while cutting shows good technique. This thought also prevails during iaido exhibitions. With the exception of experts, it is generally believed that an emitted sound is wonderful.If a sword has a groove there is the chance that it will alert your opponent during the dark of night. This is not proper for high class swordsmanship, so the story goes. I have heard that a long time ago the term chi-nagare (blood flow) was used because the blood would flow down the groove as water flows down a ditch.
The presence of a groove has absolutely no relationship to whether the sword will cut well or not; however, it does have something to do with the weight and balance of the sword. The entire blade will be just a bit weaker with a groove, but dynamically speaking, it will also have more flexibility.
The overall form of a sword with a groove is gracefully elegant, and generally speaking, there are many people who like this style.
SHINOGI (RIDGE)
The height and pitch of the shinogi is relative to the blade's ability to cut well. Many factors affect a sword's sharpness or dullness, and differ according to the swordsmith. The most important aspect overall is the blade width; what is more related to this, and has become the problem, is the height of the shinogi.A sword with a high shinogi will cut thick, hard material well; however, its penetration of soft material is poor. For example, when performing suemono giri (vertical cut) on horizontally stacked material such as rolls of rice straw, the sword's ability to cut well is reduced by half.
Compared with the previous example, a sword with a flat shinogi will cut soft material well; its penetration of horizontally stacked rolled straw will be good, and its sharpness will be satisfactory. However, if you make a mistake even while using the proper tenouchi (grip), the blade will bend.
If I may offer an example, a sword named "Seki no Magoro Kanemoto" was well known as the best cutting sword. It was constructed with a flat shinogi, and the way it easily cut through material was its special feature. Both "Dodanuki" and a shin-shinto "Mito" sword were known to be sharper than Kanemoto; but, when performing suemono giri (daigiri (cutting on a platform) ), the Kanemoto cut through five stacked layered rolls of rice straw while the others came to a halt in the third roll.
That was in the case of cutting on a platform: a sword with a raised shinogi will get stuck, which is a bad fault. The sharpness may be the same, but the proof is in the height difference of the shinogi. A blade with a high shinogi is suitable for actual combat as well, but in the case of platform cutting, a definite difference becomes clear.
In essence, a sword with a wide blade and flat shinogi will have perfect sharpness.
When cutting bamboo, the cutting ability of a sword with a high shinogi will not significantly change. Its flexibility will be strong, and is suitable for bamboo. On the other hand, a flat shinogi has no flexibility and is unsuitable for cutting bamboo. When one's hasuji or tenouchi are wrong, the blade will often bend.
In short, test cutting is similar to cooking. Different kitchen knives are used according to what is being prepared. A knife with a thick "back" will be used for hard vegetables and meat; a knife with a thin "back" will be used for soft items such as greens.
I have traveled the length and breadth of Japan not just to test the sharpness of swords, but to express my thoughts and experience in my special area of kireaji. I particularly wanted to write about the ideal sword for actual use; however, because this field is so broad, I have only presented an abridgment.