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Today's Sword Term: "Hi" or "Groove"

Like other bladed weapons developed across the world, the Japanese Katana was designed to be flexible, strong and resilient. For example, the swordsmiths’ use of “shingane,” the soft and flexible form of tamahagane, gives the katana its resilient flexibility. In contrast, the use of “kawagane,” the harder tamahagane that makes up the outer casing of the sword metal, provides the sharp cutting edge that has become legendary.

Although we are mesmerized by the construction of the katana and may be tempted to assign otherworldly qualities to it, the Japanese Sword is nothing more than the absolute perfection of craft through trial and error, eventually resulting in unmatched metallurgical skill. There are, however, many components of the Japanese Sword that are shared with bladed weapons found around the world.

Today we’ll focus on the "hi" (pronounced "hee") or groove that is sometimes found on Japanese Swords. One might hear this referred to as a “blood groove,” but this interpretation is misguided; the history of the hi is found in the technology of the blade itself. Initially, these grooves were carved into blades to increase blade rigidity. If we looked at a cross section of a blade with hi, we would see that the shape resembles a modern day “I” beam, a shape developed due to its incredible strength-to-weight ratio. Hi performed much of the same function on a blade as “I" beams perform in modern building materials: the shape increases rigidity while reducing weight. We can see that the "hi" design's functionality was also championed in bladed weapons from around the world. The fuller groove (pictured below), similar to the Japanese hi, is present in many European weapons for the exact same purpose - blade rigidity and weight reduction.

European sword with fuller groove

Although the hi was based in practicality, it soon became to be regarded as decoration. John Yumoto describes eight different types of hi in “The Samurai Sword Handbook” (an excellent resource for anyone who wishes to understand the Japanese sword):

  1. Bo-hi: Wide groove

  2. Futasuji-hi: Two narrow grooves

  3. Bo-Hi ni tsure-hi: Wide and narrow grooves

  4. Koshi-hi: Short groove

  5. Gomabashi: Two short grooves

  6. Shobu-hi: Joint-end twin grooves

  7. Kuichigai-hi: Joint-end irregular double grooves

  8. Naginata-hi: Halberd grooves

Yumoto also describes the different ways that hi could end on the blade:

  1. Kaki-toshi: Chiseled through

  2. Kaki-nagashi: Chiseled halfway

  3. Maru-dome: Round end

  4. Kaku-dome: Square end

Also, Yumoto states that “a groove tip extending past the yokote is called hiaki-agari: a groove tip stopping short of the yokote is called hisaki-sagari. The area in the upper surface not chiseled out is called chiri. A groove may have chiri on both sides or only on one side.” (Yumoto, 1958)

In modern times, hi have mostly become a matter of personal preference- most manufacturers will provide models that include different type of hi to suit the individual swordsman's desire, while exceptionally long blades benefit from the weight reduction that the hi can provide. Hi are now exceptionally common on iaito, or practice swords. The Hi will help the practitioner determine the correct angle of their cut: a loud whistle, or tachi kaze indicates that the sword is being swung with correct hasuji, or blade angle.

Rooted in metallurgic functionality, the hi provides a beautiful feature that remains relevant to Japanese Sword practitioners to this day and reminds us that, as with our practice, it is sometimes what we take away - not what we add - that makes us stronger.

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