Ku (Machi) and Machi-okuri: How Blade-ku and Ridge-ku Shapes Reveal the Era and Appraisal Significance of Japanese Swords
* Image is for illustrative purposes only.Table of Contents
What is ku (machi)? —— The Boundary Separating the Blade and Tang
At the boundary between the blade and tang (nakago) of a Japanese sword, there is a step called "ku (machi)". This ku has two elements.
Ha-machi: The step on the edge (blade edge) side. The starting point where the cutting edge begins.
Mune-machi: The step on the mune (spine) side. The starting point where the ridge line of the mune begins.
The ha-machi and mune-machi are positioned facing each other, but they are not necessarily at the same height. The straight-line distance from ha-machi to mune-machi (the width in the direction perpendicular to the blade) is sometimes called "machi-haba".
The ku serves not only as a morphological boundary but also as a "stop" when fixing the blade to the tsuka (handle). In combination with the mekugi-ana (peg hole), it controls the axial movement of the blade and is an important functional element in practical use.
Shape Classification of ku —— The First Step in Reading the Era
The shape of ku has characteristics depending on the era, region, and school, making it an important determinant in authentication. The main shape classifications are as follows.
Shapes of Ha-machi
Chokkaku-machi (right-angle ku): The ha-machi is cut almost perpendicular to the blade axis. A standard shape seen on swords from many eras.
Naname-machi (slanted ku): The ha-machi is set at an angle to the blade axis. Seen on some swords from the Kotou (old sword) period.
Marumi-machi (rounded ku): The shape where the ha-machi has rounded edges. Repeated polishing can also cause a right-angle ku to become rounded.
Shinogi-ochi-machi (ridge-drop ku): The shape where the shinogi (ridge) line drops (falls) near the ku. A unique shape seen on hirazukuri swords.
Shapes of Mune-machi
Suguha-mune-machi (straight mune-ku): The shape where the mune-machi is set in a straight line. The most common type.
Iri-mune-machi (inward mune-ku): The shape where the mune-machi recedes slightly inward into the blade.
Hari-mune-machi (protruding mune-ku): The shape where the mune-machi protrudes slightly outward from the blade.
As a chronological trend, fine examples from the Kamakura period have clear, deep ku shapes. From the Muromachi period onward, mass-produced swords tend to have shallower ku. In the Edo period, carefully crafted swords show clear ku shapes again.
Machi-okuri —— Evidence Inscribed by Polishing History
"Machi-okuri" is one of the important concepts in Japanese sword authentication. This refers to a polishing technique where the ha-machi and mune-machi are intentionally sharpened to shorten the blade. It is characterized by the fact that instead of shortening the tang (nakago), only the ku is raised while leaving the tang in its raw state. The degree of this is called "machi-okuri-ryo" (amount of ku displacement).
Methods for Determining Machi-okuri:
- Confirm the direction of the ha-machi and mune-machi surfaces and their cutting quality. If the displacement amount is large, the ku surface becomes dull.
- Measure the distance from the mekugi-ana (peg hole) on the tang to the ku, and compare with swords from the same era and style.
- Confirm the positional relationship between the tsuka (handle) of the koshirae (sword mounting) and the ku. Swords with large machi-okuri may have an unnatural fit with the handle.
- Observe the shape changes in the transition from the ku to the tang.
Evaluation by Amount of Machi-okuri:
- Little to no machi-okuri (less than 1mm): Few polishing events. The blade may have high structural integrity.
- Moderate machi-okuri (1-5mm): Appropriate polishing for conservation has been performed. A standard condition.
- Large machi-okuri (over 5mm): Evidence that the sword has been polished many times in the past. The blade length may be shorter than originally.
Both machi-okuri and suriage (cutting and shortening of the tang) are techniques for shortening the blade, but they differ in how the tang is treated. Suriage shortens the entire blade by cutting the tang, whereas machi-okuri is a technique that leaves the tang in its raw state and only raises the ku.
What Can Be Learned from Observing the ku
Information about the sword's history of use can also be obtained from the condition of the ku.
ku of functional swords: Near the ku of swords actually drawn from and resheathed in the saya (scabbard), friction marks from the inner walls of the saya (habaki-shita) may be engraved. In particular, when fine wear is visible near the mune-machi, corresponding to the lower edge of the habaki, it can be considered evidence of frequent use.
Distribution of forging flaws (kiizu): The area around the ku is a location where stress tends to concentrate during forging, and it is also a place where minor defects and fatigue from forging are likely to occur. Pay special attention to any irregularities in the grain pattern from the ku to the ha-machi.
Condition of rust (sabi): Where rust begins on the blade reveals the storage conditions. If rust originates near the ku, it is possible that the area below the habaki was not properly dried or maintained.
Comprehensive Authentication of ku and Tang (nakago)
It is important to observe the ku not in isolation, but as an integrated whole with the entire tang (nakago).
Continuity of ha-machi and yasuri-me (file marks): If the yasuri-me (file mark) pattern on the tang begins slightly below the ha-machi, there is a high possibility that the original tang shape from manufacture has been preserved.
Relationship between mekugi-ana position and ku: The distance from the mekugi-ana to the ku (the mekugi-section) shows certain tendencies depending on the era and school. If this distance is too long or too short, the possibility of suriage or post-manufacture work should be considered.
Consistency between mei (signature) and ku: There is a difference in meaning depending on whether the mei is engraved very close to the ku or at a distance from it. On swords with large machi-okuri, the ku may come too close to the mei.
The ku, a small part of the sword, is a silent witness to the history of the Japanese sword. By carefully observing its shape, condition, and position, a complete picture emerges of the polishing history, storage conditions, and history of use from the time of manufacture to the present day.
Difference Between Suriage and Machi-okuri —— Comparison Table
| Item | Machi-okuri | Suriage |
|---|---|---|
| Area worked on | Ha-machi and mune-machi are sharpened toward the kissaki (point) | Nakago-jiri (tang end) is shortened |
| Condition of tang | Remains in raw state | Becomes shorter |
| Blade length | Becomes shorter | Becomes shorter |
| Effect on mei | Principally remains | Lost in large suriage (preserved through effort using額銘 or 折返銘) |
| Treatment in authentication | Treated as equivalent to raw, but noted as "machi-okuri" | Clearly distinguished and evaluated as "suriage" or "o-suriage" |
Frequently Asked Questions
What is ha-machi?
The step set on the edge side at the boundary between the blade and tang (nakago). It is the starting point of the cutting edge and the reference point where the habaki is placed.
What is mune-machi?
The step set on the mune (spine) side at the boundary between the blade and tang. It pairs with the ha-machi, and the habaki is placed on these two ku to fix the blade. The depth and clarity of the ku are important clues for determining the era.
What is machi-okuri?
A technique of sharpening the ha-machi and mune-machi in the direction of the kissaki to shorten the blade length. Since the tang end is not cut, the tang remains in its raw state. It has been performed to address damage or wear at the blade's edge, or to refurbish swords to fit specific dimensions.
Does a sword with machi-okuri lose value?
It depends on the degree. If the raw tang and authentic mei are preserved, the evaluation does not drop as much as with suriage, but large amounts of machi-okuri move the sword away from its original form, so it is considered in terms of structural integrity. It is standard authentication practice to check for evidence of machi-okuri or suriage when the blade length on the registration certificate differs significantly from measured values.
What is the relationship between habaki and ku?
The habaki is a metal fitting placed on the ha-machi and mune-machi to fix the blade in the saya (scabbard), using the ku as the starting point to fix the blade in the scabbard. When the ku wears, the habaki becomes loose. Therefore, the condition of the ku and the fit of the habaki should always be observed together. Looseness is addressed by making a new habaki or refitting it, and the ku itself is not sharpened to adjust the fit.
