The Technique of Hi Carving — The Role of Blade Grooves and the Craft of Cutting Bo-hi and Futasuji-hi

The Groove Running Along the Blade: "Hi" (樋)

When you look at the flat areas (hiraji) or ridge areas (shinogiji) of a Japanese sword, you sometimes see long, narrow grooves carved running along the edge. These are called "hi (樋)". It uses the same character as the guttering on a roof (amadobi), referring to the groove-like carving cut into the blade.

The hi is not merely decorative. It is a form of blade carving (horimono) that serves both functional and aesthetic purposes.

The Purpose of Hi: Weight Reduction and Rigidity

The primary practical purpose of carving hi is weight reduction. By removing a portion of steel from the blade, the sword can be made lighter without significantly compromising sharpness or strength. The longer the blade, the more weight becomes an issue, making the weight-reduction effect of hi particularly valuable.

Moreover, by carefully shaping the cross-section, the hi is said to also balance the flexibility and rigidity of the blade. Adding a groove changes how the sword responds to bending toward the ridge even at the same weight. Additionally, the air flowing along the hi as the sword is swung is said to produce a sound known as "tachikaze (太刀風)", or sword wind.

Types of Hi

There are many types of hi, each named according to its shape. Here are the most representative.

Bōhi (棒樋) is the most basic form: a single, straight, relatively wide groove running along the blade. Futasuji hi (二筋樋) consists of two narrow grooves carved parallel to each other. Kōshi hi (腰樋) is a shorter groove carved only in the hip area closer to the tang. There are also more elaborate forms, such as sōe hi (添樋), which places a thin auxiliary groove next to a bōhi, or grooves that contain relief carving like kurikara (倶利伽羅) dragons within the main groove.

The combination of these types, along with the width, depth, and termination of the groove, significantly changes the overall appearance of the blade.

The Process and Tools of Carving Hi

Carving hi is called "hi wo kaku (樋を掻く)". It is painstaking work using specialized steel blade-like tools such as a tagane (鏨) chisel or suki (鋤) scraper to gradually remove the jigane (地鉄—body steel) of the blade.

Carving hi requires considerable skill: the grooves must be symmetrical on either side of the blade's centerline and maintain consistent width and depth throughout. Any wavering in depth or deviation from center ruins the appearance of the entire blade and is difficult to correct. Hi are most often carved before the hardening process, making carving errors unforgivable—it is literally a one-shot operation.

Craftsmanship Revealed in Groove Termination

The craftsmanship of both the swordsmith and carver is visible in how the groove ends—in the treatment of the groove terminus (hisaki, 樋先). There are several ways to terminate a groove: a "marudome (丸止め)", or rounded end, a "kakitōshi (掻き通し)", where it extends toward the point, or terminations that stop before the crossguard (yōkote).

How the groove terminates on the tang side—whether it runs all the way into the tang or stops near the edge-section (ha-ku, 刃区)—along with the overall refinement of the groove work, serves as a measure of the work's quality. A cleanly finished groove terminus speaks to the carver's concentration and skill.

Later-Carved Grooves: The Category of "Atōhi" (後樋)

Not all hi are carved during the sword's original manufacture. Grooves added later—carved in subsequent eras for weight reduction or aesthetic improvement—are called "atōhi (後樋)" and are distinguished from original grooves. In general, several observational points help determine whether a groove is original or later-carved: the proportion of the groove to the blade's overall form, the relationship of the groove terminus to the crossguard and machi (区—the blade-tang junction), and the chronological relationship to any re-hafting (suriage, 磨上げ).

Being an atōhi does not immediately diminish a blade's value, but it is important information for understanding what the sword looked like when originally made, and is often mentioned in references and appraisals. When examining hi, asking "when was it carved?" adds another dimension to your observation.

Care and Condition Assessment of Swords with Hi

Because hi are grooves, they readily collect oil and moisture. During care, it is important to carefully wipe the inside of the groove with soft paper or cloth along its length to ensure no old oil remains. If rust spots appear inside the groove, they are difficult to remove and may spread if neglected. When inspecting, shine light deep into the groove to assess its condition.

Additionally, the groove exposes the interior of the jigane (body steel) to the surface. Because carving hi reveals the blade's interior, forge cracks or other flaws can emerge in the groove. When considering purchasing, it is prudent to inspect not only the flat areas and hamon (刃文—blade pattern) but also the condition inside the groove, using both photographs and in-person examination.

Checklist for Examining Hi

When examining a sword with hi, it is helpful to check the following points in order.

• Does the width and depth of the groove remain consistent from the handle to the point?
• Are the edges of the groove crisp and sharp, not rounded or sagging?
• What is the style of groove termination, and are its proportions to the crossguard and machi correct?
• Are there no rust, flaws, or polishing residue inside the groove?
• Are the grooves on both sides of the blade aligned and similarly executed?

Simply being aware of these points when examining a blade will reveal the quality differences between individual swords, even among those with the same type—such as bōhi.

The Crystallization of Functional Beauty

Though born from the practical need for weight reduction, the hi embodies a unique beauty as a single groove running along the blade. In its simultaneous fulfillment of function and decoration lies the marriage of the Japanese sword's rationality as a tool and its refinement as a work of art.

By observing the width and termination of the groove carved into a blade, you can discern what the maker prioritized—lightness, beauty, or the balance of both. The hi is a key to understanding the swordsmith's design philosophy.

Understanding Sword Craftsmanship

TOUKENZA (operated by M-Assets Co., Ltd.) is an online marketplace for Japanese swords. Understanding the craft of sword-forging opens doors to deeper appreciation of individual blades. Swords currently listed can be viewed in our online catalog and are available for purchase. If you have questions about a particular blade or any other inquiries, please feel free to contact us through our inquiry form.