Shobu Zukuri: When the Shinogi Runs to the Point Without Yokote

The "tsukurikomi" (construction) of a Japanese sword refers to the three-dimensional structure of the blade as viewed from the side and in cross-section. In addition to basic forms such as shinogi-zukuri, hira-zukuri, and kirisaki-zukuri, numerous variations derived from different eras and purposes exist. Among them, "shobu-zukuri" is known as a construction method favored by connoisseurs due to its difficulty in identification, despite the elegance of its name.

Morphological Features of Shobu-zukuri

The greatest characteristic of shobu-zukuri is that it lacks a yokote-suji. Typically, a shinogi-zukuri blade has a line called yokote drawn at the boundary between the kissaki and the main body of the blade, with the ko-shinogi and boushi formed beyond it. In contrast, shobu-zukuri forgoes the yokote, with the shinogi-suji running straight through to the tip of the kissaki. This form is named for its resemblance to the elongated, slender leaf of the iris.

Because there is no yokote, the kissaki and blade body form a continuous, flowing curve, creating an overall impression of slenderness and elegance. Although it is a shinogi-zukuri, the visual separation of the boushi is absent, making it difficult for the untrained eye to distinguish it from ordinary shinogi-zukuri.

Shinogi-zukuri and Unokubi-zukuri Comparison

Shobu-zukuri belongs to shinogi-zukuri in terms of cross-sectional structure. In other words, the basic form is shared, in which a ridge called shinogi-suji runs between the ha-side and mune-side. The difference comes down to a single point: the presence or absence of yokote. If there is a yokote, it is ordinary shinogi-zukuri; if there is not, it is shobu-zukuri. This is the most practical method of differentiation.

One form often confused with it is unokubi-zukuri. Unokubi-zukuri is made by partially removing the metal on the mune-side to create a constricted form resembling a cormorant's neck, with the change in mune thickness serving as the distinguishing feature. Whereas shobu-zukuri is "a smooth form without yokote," unokubi-zukuri is distinguished by "the unevenness of the mune." It is important to note that the observational axis differs between the two.

Organization with Other Variant Forms

Once you understand shobu-zukuri, it becomes easier to retain the knowledge by arranging it alongside other variant forms.

• Kanmuri-otoshi-zukuri: A construction in which the metal on the mune-side of roughly the upper half of the blade is thinned by shaving, seen on tanto and other short blades. The concept is similar to unokubi-zukuri, but there are differences in the manner and extent of shaving.
• Moroha-zukuri: A construction on tanto in which a blade is also attached to the mune-side near the tip, seen in works from the Muromachi period.
• Osoraku-zukuri: An unusual form in which the kissaki occupies a large portion of the blade.

If you view all of these as "variations derived from the basic forms of shinogi-zukuri and hira-zukuri," it becomes easier to sketch a map of tsukurikomi as a whole. Variant forms are few in number, which is why the accuracy with which one can grasp their meaning when they appear in product descriptions or certificates of authentication marks a difference in understanding.

Time Periods and Examples of Appearance

Shobu-zukuri is said to have appeared occasionally on tachi and wakizashi of Bizen and Mino smiths from the middle to late Muromachi period. In terms of numbers, it was never common, appearing as an exceptional and decorative choice alongside the overwhelming majority of shinogi-zukuri and hira-zukuri.

While there is no established theory as to why it appeared in this period, it is thought to have been a design innovation to introduce variation in form among mass-produced Muromachi-period swords. Because it is difficult to make definitive statements about specific surviving pieces or designated objects, the understanding here remains at the level of morphological features.

Distinguishing from Wear and Sharpening—A Common Pitfall of Misidentification

Something to be cautious about in actual appreciation is the existence of shinogi-zukuri blades where the yokote has become shallow over many years of sharpening, appearing at first glance to be shobu-zukuri. The yokote is a line that the sharpener re-establishes with each sharpening, and on blades that have undergone significant sharpening or repeated re-sharpening, the line may become ambiguous.

In contrast to true shobu-zukuri, which is designed from the outset without a yokote, blades where the yokote has become faint from sharpening wear often retain unnaturalness in the traces of ko-shinogi and the placement of metal around the kissaki. When judgment is uncertain, it is best to examine the return of the boushi, whether the width of the shinogi-ji continues naturally to the tip, the fullness of the fukura, and other such points comprehensively. For products with photographs posted online, confirming the presence or absence of the yokote and the quality of the line through an enlarged image of the kissaki portion is the first step.

Organization of Terms Useful for Observation

By grasping these fundamental terms, you can read product descriptions and certificate language accurately, and naturally your precision in determining tsukurikomi improves. The most efficient learning method is to go back and forth between terms and actual photographs.

Observation Points in Appreciation

When appreciating and determining shobu-zukuri, it is good to first check whether there is a yokote line near the kissaki. If the line is not found and the shinogi-suji continues unobstructed to the tip, the likelihood of shobu-zukuri is high. Additionally, whether the overall blade width is narrow and describes a gentle curve serves as a supplementary clue.

Tsukurikomi is a fundamental observation item, along with sori and kissaki, in reading the form of a blade. Understanding a variant form such as shobu-zukuri will deepen one's eye for viewing the form of a sword. On our site, blades currently on offer are posted in an online catalog with photographs, which can be used as an entry point for comparing the differences in tsukurikomi through images.