Reading Sword Blade Construction—Types and Historical Background of Shinogi-Zukuri, Hira-Zukuri, Kiriha-Zukuri, and Kata-Kiriha-Zukuri

Tsukurikomi: Determining a Sword's Form

When discussing Japanese swords, the first thing that catches the eye is their overall form—the depth of the curve, the length of the blade, the shape of the point, and other general contours. Yet equally important is the cross-sectional shape of the blade itself, in other words, "tsukurikomi." Tsukurikomi refers to the concept of finishing forged steel into a particular cross-section, and it directly affects everything about the sword: its sharpness, strength, weight balance, and function. Even two swords of identical dimensions will feel completely different in hand and behave entirely differently when cutting if their tsukurikomi differs.

Japanese swordsmiths have used different tsukurikomi across eras, regions, and individual commissions. This knowledge is essential for modern appreciation, and understanding tsukurikomi reveals the historical context and creative intent behind each sword with striking clarity.

Shinogi-zukuri: The Mainstream Standard of Tsukurikomi

The quintessential tsukurikomi of Japanese swords is shinogi-zukuri. A ridge called the shinogi runs along the side of the blade, and the cross-section forms a roughly diamond-like shape. The edge side of the shinogi is called the shinogi-ji, and the spine side continues as the mune (spine), with an edge area called the mune-machi. This ridge provides longitudinal rigidity to the blade, achieving a structure that is both light and resistant to bending.

Shinogi-zukuri is employed in the majority of uchigatana and tachi, appearing widely from Sengoku-period battlefield blades to Edo-period daimyo-mounted swords. In authentication, the height and width of the shinogi serve as clues to identifying school and period characteristics. For example, Bizen-tradition tachi typically have a relatively low, smoothly transitioning shinogi, while Soshu-tradition works often feature a high, prominent "takashinogi" (high shinogi). Even the finest details of the shinogi become important indicators in regional authentication.

Hira-zukuri: Concise Beauty for Tantō and Wakizashi

Hira-zukuri is a cross-section structure without a shinogi—quite literally flat. Because both sides of the blade connect directly to the edge without the shinogi, the cross-section becomes a relatively thin wedge shape. Compared to shinogi-zukuri, it lacks longitudinal rigidity, but on short blades, strength is rarely compromised. Consequently, it has been widely adopted for tantō and wakizashi.

Hira-zukuri tantō thrived from the late Kamakura period through the Nanboku-chō era, with many produced in substantial sizes. During this period, each section of the blade was decorated with bold, irregular ha-mon (temper patterns), which combined with the clean lines of hira-zukuri to create powerful beauty. Hira-zukuri tantō by renowned Soshu-tradition masters such as Masamune and Yukimitsu exemplify this style, with numerous examples designated as National Treasures or Important Cultural Properties.

Hira-zukuri also has advantages for observing the ha-mon and jigane (steel surface). Without the step created by the shinogi, the surface texture and utsuri (shine pattern) of the jigane are more easily observed straight on, making it arguably easier for viewers to appreciate.

A derivative of hira-zukuri is also known as shobu-zukuri. A ridge runs from the habaki base to the tip, resulting in a slender form resembling the blade of a Japanese iris, favored for longer wakizashi, its refined silhouette harmonizing well with samurai formal dress.

Kiriha-zukuri: A Dignified Construction Retaining Echoes of the Koto Period

Kiriha-zukuri is classified as a variation of shinogi-zukuri. While standard shinogi-zukuri has the shinogi running through the middle of the blade, kiriha-zukuri positions the shinogi at a low point near the edge. As a result, the edge side has a steep angle, while the spine side forms a gradual, broad surface—creating an asymmetrical cross-section, so to speak.

This construction is frequently seen in tachi from the late Heian through early Kamakura periods and represents one of the characteristic styles of the koto (old sword) era (roughly before the Keichō period). When a deeply curved, long-bladed tachi combines this kiriha-zukuri, it conveys an old-fashioned martial presence befitting use from horseback. Examining surviving ancient tachi reveals transitional works that retain echoes of kiriha-zukuri while gradually shifting toward shinogi-zukuri—fascinating historical materials for understanding the formation of Japanese sword aesthetics.

Katakiriha-zukuri: A Rare Construction with Angles on One Side Only

Katakiriha-zukuri is an extraordinarily rare cross-sectional construction featuring asymmetry: one side is hira-zukuri (no shinogi) while the other side is kiriha-zukuri (with shinogi). When viewing the cross-section, one side spreads flat, while the other has a low ridge. This construction is renowned for appearing in tantō by the famous Kamakura-period master Kagemitsu of Bizen, and it remains known in connoisseur circles today as "Kagemitsu's katakiriha-zukuri."

One theory about why such an asymmetrical form exists suggests it intentionally limited the direction of the cutting force, optimizing the blade for specific uses or ritual movements. In any case, it represents a construction prioritizing individual, functional beauty over versatility. Some modern swordsmiths have taken up the challenge of katakiriha-zukuri, yet its difficulty means few have mastered it, making it a rare and highly prized domain.

Tsukurikomi and Historical Context: Why Has Form Changed?

The evolution of tsukurikomi is not merely a matter of stylistic fashion but is deeply connected to changes in combat methods, social structure, and material technology across eras.

From the Heian through Kamakura periods, the age of mounted warriors saw long tachi designed for slashing downward from horseback as the mainstream, with kiriha-zukuri and older-style shinogi-zukuri in wide use. Entering the Nanboku-chō period, infantry-based collective warfare increased, driving demand for shorter, more maneuverable blades and tantō. Hira-zukuri flourished during this era.

By the Edo period, opportunities for actual combat had become rare, and swords took on greater importance as "sashiryō" (worn regalia) signifying a samurai's status. In tsukurikomi, practical considerations alone gave way to emphasis on beauty, rarity, and school tradition. While shinogi-zukuri remained mainstream, hira-zukuri or variant constructions were sometimes deliberately chosen for custom tantō and fittings to harmonize with design aesthetics.

The shape of the kissaki (point) also reflects its era.

• Early to mid-Kamakura slender tachi featured the small kissaki (treasured by court nobility)
• Nanboku-chō great swords featured the large kissaki
• Muromachi battlefield blades, designed to penetrate armor, featured the inokubi-kissaki (wild-boar-neck point)

For tantō, an inward curve called uchiori also exists on the blade side, known as a construction for portability and self-defense, exemplified by the kikuchi-yari type tantō.

Cultivating the Eye to Read Tsukurikomi

Observing tsukurikomi begins well with confirming the presence and position of the shinogi. If a shinogi is present, one can broadly determine it as shinogi-zukuri or kiriha-zukuri; if absent, hira-zukuri. Furthermore, examining the height, width, and proportion of the shinogi to the overall blade allows one to venture into estimating the production period and school.

When viewing Japanese swords in museums or art galleries, try consciously shifting the display case angle to observe the edge side, spine side, and areas near the cross-section. Depending on how light strikes, the shinogi ridge emerges more clearly, allowing the three-dimensional quality of the tsukurikomi to be grasped more vividly. Simultaneously, noting whether the surface texture of the jigane and the character of the ha-mon harmonize with the tsukurikomi becomes an important observation point.

The Japanese sword is, in totality, a single artwork, and tsukurikomi is its structural skeleton. By understanding tsukurikomi alongside other elements—silhouette, curvature, ha-mon, and sculptural ornamentation—the depth of the story a single blade carries increases all the more. Beginning by asking "which tsukurikomi does this sword possess?" should open new doors to appreciation.