Bōshi Quenching: Shaping the Hamon at the Kissaki — The Swordsmith's Most Demanding Step

Sword Tip Hamon "Boushi"

The hamon of a Japanese sword runs along the entire blade, but the hamon that appears on the kissaki (sword tip) is given the special name "boushi" (literally "hat"). It refers to the hamon that curves around the point from the yokote, and corresponds to the continuation of the blade's hamon as it extends to the kissaki.

The boushi is highly valued both in appreciating swords and in sword-making technique. This is because the boushi is the area where the skill or lack thereof in hardening is most blatantly evident.

Why is the Sword Tip Difficult to Harden?

Hardening (yakiire) is the process of creating hamon by applying yakiba-tsuchi to the blade in layers, then heating and rapidly cooling it in water. By covering the edge side with a thin layer of clay and the spine (mune) side with a thicker layer, only the edge hardens and the hamon is created.

However, the kissaki differs greatly in its conditions from other parts of the blade. First, as the kissaki tapers to a point, the steel becomes thinner, so heat dissipates more readily during rapid cooling, making it easy to over-harden. When hardening is excessive, the steel becomes brittle, and in the worst case, the kissaki can chip or crack.

Furthermore, the kissaki is the part of the sword that bears the most practical stress, so both hardness and toughness are especially required. Even the slightest error in clay placement can result in "burn-off," where the boushi's hamon disappears midway, or conversely, excessive hardening that makes it brittle.

Yakidume and Komaru—Differentiating Boushi Appearance

The boushi has several forms (shapes), which the swordsmith intentionally differentiates. The typical types are as follows.

There are also many other types, including boushi with mixed patterns and those accompanied by hakikake.

These boushi forms are determined by the shape and quantity of yakiba-tsuchi applied to the kissaki and the rate of cooling. The swordsmith carefully applies clay to the kissaki while considering harmony with the blade's overall hamon.

Practical Steps for Observing the Boushi

There is a certain technique to appreciating the boushi. First, hold the blade up to a point light source (light from a single point, such as a lamp), and while tilting the kissaki slightly toward the light, trace your gaze from the yokote to the tip. Since the appearance of the hamon changes greatly depending on the angle of light reflection, the key is to gradually adjust the angle and find the position where the hamon appears to stand out in white.

There are three points to verify.

1. Does the hamon continue clearly from the yokote all the way to the kissaki?
2. What form does the hamon take at the tip—komaru, omaru, or yakidume?
3. The depth of the curve-back—how far down the mune side the curved-back hamon extends?

By tracing these three points in order, you will be able to explain the boushi's appearance in your own words, raising your appreciation to the next level.

The "Workings" That Appear in the Boushi

The boushi not only shows the outline of the hamon but also displays fine details within the edge such as nie and nioi. When streaky workings resembling a broom stroke are visible along the boushi's hamon, it is called "hakikake" and creates a unique visual. These workings are expressions of the swordsmith's individual style and serve as material for considering schools and lineages of sword makers.

However, these are also delicate details that are difficult to capture in photographs. When examining a sword through images, it is best to compare magnified images of the kissaki from multiple angles and confirm any unclear points with the seller.

Saiha and the Boushi—Clues to Determining Condition

Re-hardening a sword that has lost its hamon due to fire or other damage is called "saiha." Swords that have undergone saiha often show unnaturalness in the hamon near the boushi and the hamachi (edge-spine junction), and historically, the boushi has been one of the clues for identifying saiha. This is one reason why the boushi is said to be "an area that speaks to the health of the sword."

The Importance of the Boushi in Authentication

The boushi is an important clue for distinguishing schools and periods in sword authentication (kantei). As mentioned earlier, yakidume is characteristic of Yamato swords, and the boushi's form often reflects the maker's lineage.

Furthermore, even swords that have undergone suriage (shortening of the tang) often retain the kissaki's boushi, and the quality of the boushi can also serve as a gauge for the sword's condition. Whether the boushi remains intact and well-hardened is important information about the state of the sword.

Technique Concentrated at a Single Point

The boushi is a single point where the entire blade's hardening technique is ultimately concentrated. Even if the broad blade is hardened beautifully, failure at the kissaki's boushi will greatly lower the work's appraisal. For this reason, the swordsmith devotes maximum concentration to the kissaki at the final stage of clay application.

Please hold the completed sword's kissaki up to the light and trace the boushi's curve-back. In just a few centimeters of hamon, the concentration of the swordsmith who faced the once-only challenge of hardening is condensed.

Experiencing Sword Craftsmanship

TOUKENZA (operated by M-Assets Inc.) is an online sword marketplace for selling Japanese swords. Understanding the techniques of sword making is a key to more deeply appreciating each sword. The swords we carry can be viewed in our online catalog and are available for purchase. If you have any questions about a particular sword or any other inquiries, please feel free to contact us through our inquiry form.