U-no-kubi-zukuri: Tanto and Wakizashi with a Constricted Back Ridge — Kamakura and Nanboku-cho Styles

Among the various construction methods of Japanese swords, one known for its distinctive name is u-no-kubi-zukuri (鵜の首造り). The name derives from the slender, elongated neck of the cormorant, a water bird, and the peculiar constriction visible when viewing the blade from the spine side defines this construction method.

The Form of U-no-kubi-zukuri

U-no-kubi-zukuri is a construction method in which the area between the shinogi ridge and spine (shinogi-ji) is stripped away around the middle of the blade, making the spine thin and constricted. Specifically, the kissaki (point) and the spine in the lower half are left thick, while the shinogi-ji area between them is stripped away by scooping. As a result, the contour on the spine side narrows in the middle and swells again near the point. This rise and fall evokes the neck of a cormorant.

When viewed from the spine side, the upper half displays a prominent shinogi ridge with the spine-adjacent area becoming thin, but as the blade approaches the point, the shinogi-ji area becomes thick again. This two-stage change—becoming thin and then recovering—is the key to identifying u-no-kubi-zukuri. The spine itself continues to the point.

Period and Sword Type

U-no-kubi-zukuri is said to be a construction method frequently seen in short swords and side swords from the Kamakura period through the Nanbokucho period. This period corresponds to when numerous masterpiece short swords were produced, with workmanship marked by both change and innovation. By stripping the spine material, the point becomes lighter and sharper, increasing its suitability for thrusting, while the stripping itself imparts character to the blade's appearance. It can be called a construction method that unites both practical function and sculptural form.

The concentration of this construction in short swords and side swords rather than long swords is thought to be because the shorter blade length means that stripping the spine creates less structural risk, and elaborate construction is easier to achieve.

Distinction from Kamuriottoshi-zukuri

U-no-kubi-zukuri is easily confused with kamuriottoshi-zukuri (冠落造り). While both share the characteristic of stripping spine-side material, the critical difference lies in the character near the point. In kamuriottoshi-zukuri, the spine that becomes thin in the upper half remains thin all the way to the point. In u-no-kubi-zukuri, the spine that once becomes thin and constricted becomes thick again near the point.

Therefore, the practical procedure for distinction is as follows: first, confirm whether there is a thin section where the spine has been stripped; next, trace whether that thinness continues to the point or recovers midway. If thickness returns at the point, it is u-no-kubi-zukuri; if it tapers thin, it is kamuriottoshi-zukuri.

Fundamentals of Construction—Major Types and Classification

To understand u-no-kubi-zukuri, it helps to have an overall grasp of tsukurikomi (造込み) types. Tsukurikomi is a term referring to the cross-sectional structure and forming method of a blade, and the major types are as follows.

• Shinogi-zukuri (鎬造り)—The most standard construction method, with a shinogi ridge running along the blade's side profile. The majority of tachi and uchigatana are of this type.
• Hira-zukuri (平造り)—A flat construction with neither shinogi ridge nor yokote. Most common in short swords.
• Shobu-zukuri (菖蒲造り)—Similar to shinogi-zukuri but lacking a yokote, with a profile resembling an iris leaf. Seen in side swords and similar blades.
• Kamuriottoshi-zukuri (冠落造り)—A construction where the spine-side upper portion is stripped, tapering thin all the way to the point.
• U-no-kubi-zukuri (鵜の首造り)—A construction where the spine-side middle constricts and thickness returns near the point; the subject of this article.

In the realm of short swords and side swords, construction variation is especially rich, and even blades of the same length can have their appearance transformed by a single construction difference. Beyond merely memorizing construction names, when you view them while considering why that form was chosen—whether for weight reduction, thrusting ability, or decorative effect—the swordsmith's intent becomes discernible.

Terminology—Shinogi-ji, Kasane, and Fukura

Grasping several basic terms makes explanations of construction more understandable. Shinogi-ji (鎬地) refers to the plane between the shinogi ridge and spine, kasane (重ね) refers to the blade's thickness, and fukura refers to the curve of the edge at the point. In the description of u-no-kubi-zukuri, "stripping the shinogi-ji" means scooping out this plane between the shinogi ridge and spine and partially reducing the blade's thickness. Changes in thickness are difficult to discern in front-facing photographs, which is why observation from the spine side or at an angle is necessary.

Checklist for Examining Examples and Images

When examining short swords and side swords with u-no-kubi-zukuri, it is helpful to check the following in order.

• Spine-side contour—The position where the constriction begins and ends, and whether thickness returns before the point.
• Symmetry of stripping—Whether the stripping on both sides is finished symmetrically.
• Integrity of thickness—Since this construction inherently thins the spine, blades that have been polished repeatedly may have excessive thinning.
• Period consistency—Since this construction is common in the Kamakura-Nanbokucho era, verify in the appraisal certificate that the specialist's determination aligns with the blade's appearance.

When considering an online purchase, check whether spine-side or side-profile angled images are available, and if not, requesting additional images from the seller is a reliable approach.

Appreciation and Study

U-no-kubi-zukuri is a construction method that teaches us the importance of observing the blade from directly above and from the spine side. While attention tends to focus on the hamon (刃文) and jigane (地鉄), clues for reading the blade's form are also packed in the three-dimensional information of the spine's rise and fall.

On this site, handled swords are presented online with images, and in some cases include angles that clarify the spine-side shaping. You can use these images as a means to verify differences in construction.