Yasuri-me Filing Patterns: Reading the Craftsman's Code Engraved on the Nakago

The Nakago and Yasurimi—Why Cryptic Marks Are Engraved Inside the Hilt

The nakago of a Japanese sword is normally hidden inside the tsuka and remains invisible during viewing. However, the nakago itself is the "most critical component for proving the sword's authenticity," and together with the mei, nenki, and tameshikiri-mei, the yasurimi patterns on the nakago's surface become the deciding factor in authentication.

Yasurimi are the scratch patterns left when the nakago is finished by scraping its surface with a metal file tool called a yasuri after shaping it. While functionally designed to prevent corrosion and improve adhesion to the hilt, each school and era adopted nearly fixed patterns, so "which yasurimi" functions as an authentication indicator for the school and era.

Major Types of Yasurimi

Kiri-yasuri: Yasurimi with horizontal lines running nearly perpendicular (90 degrees) to the nakago's long axis, the most basic form. Commonly seen on old swords in the Bizen and Yamashiro traditions. Subdivision depends on whether the horizontal lines are perfectly perpendicular or slightly diagonal.

Suji-kai-yasuri: Yasurimi with lines running diagonally to the nakago's long axis, widely used as an authentication term. Frequently employed by Yamato school smiths and serves as an authentication standard for Yamato swords from the old sword period.

Katte-sagari: A pattern where the yasuri lines run diagonally downward toward the ha-gawa (the blade side, viewed from the left face of the nakago). Commonly seen on shinto and shinshinto swords after the Edo period, particularly becoming the basic form widely adopted by Edo smiths.

Gyaku-katte: The reverse direction of katte-sagari—yasurimi running diagonally downward toward the mune-gawa (spine side) of the nakago. In some cases it becomes an authentication indicator because certain schools adopted it.

Oo-suji-chigai: Yasurimi with diagonal lines engraved at large angles (45 degrees or more), sometimes forming a visually prominent large cross-hatch pattern.

Kesho-yasuri: Decorative finishing where fine, regular yasurimi are applied to make the nakago's surface beautiful. Frequently applied by renowned smiths after the late Edo period to showcase their technical skill.

Comparing the above yasurimi patterns in the following organized manner makes their characteristics easier to grasp.

None of the yasurimi can determine the era or school on their own characteristics alone; they are judged comprehensively together with other elements such as mei, jigane, and hamon.

Temporal Evolution of Yasurimi—From Old Swords to Shinshinto

Yasurimi patterns change over time and are utilized as auxiliary indicators for period authentication.

Old sword period (until around 1596): Kiri-yasuri was the standard. Bizen and Yamashiro smiths used relatively fine kiri-yasuri, while the Yamato tradition frequently employed suji-kai-yasuri. The nakago was often short and corroded, making yasurimi difficult to read in many cases.

Shinto period (around 1596–1764): Katte-sagari became mainstream. Edo smiths adopted relatively uniform katte-sagari, while Osaka smiths often produced notably refined finishing.

Shinshinto period (around 1764–1876): Kesho-yasuri increased and the finishing precision of the nakago's surface showed an upward trend. Leading shinshinto smiths such as Suishinshi Masahide and Minamoto Kiyomaro finished the nakago with care as part of their artistic work.

Application of Yasurimi in Sword Authentication—How to Detect Later Alterations

Yasurimi are also effective indicators for detecting false mei and tampering. When the value of old swords surged during the Edo and Meiji periods, it became common to erase the mei on the nakago and cut a different one—"suri-age mei"—or to cut new mei on unsigned swords.

Such tampering often creates contradictions in the yasurimi in the following ways:

• The yasurimi pattern changes only around the mei (traces of scraping with a different file)
• The yasurimi direction does not match the era or school
• Old yasurimi are hidden beneath the newly cut mei (observable with fluorescent light or a magnifying glass)

In NBTHK (The Society for Preservation of Japanese Art Swords) reviews, confirmation of yasurimi is a required step in the authentication process, and when there is doubt, oblique lighting photography and microscopic examination of the nakago are performed.

When a nakago remains unaltered from its original creation—with the entire surface unscraped—it is called "ubu nakago," and since the yasurimi and mei are preserved as made, it is considered to have high historical value. In contrast, nakago that have undergone "suri-age" (resurfacing) may have lost part of the original yasurimi or mei, and the authentication certificate typically notes this.

Notes When Confirming Yasurimi

Since the nakago is housed inside the hilt, removing the hilt is necessary to directly view the yasurimi. However, drawing and reinserting the nakago risks damaging the mekugi and the nakago itself, so it should not be done lightly without professional expertise.

Additionally, patina accumulated on the nakago's surface over the years is important evidence of the sword's age and also provides clues for reading the yasurimi. If inadvertently wiped or polished, the yasurimi become difficult to read and the authentication value may be compromised, so the principle is not to clean or maintain it. When considering purchase and concerned about the yasurimi condition, it is safer to confirm via the description in the NBTHK authentication certificate or enlarged photographs of the nakago provided by the seller rather than handling the object yourself.

Contemporary Smiths' Yasurimi Selection—Tradition and Individual Expression

When creating swords, contemporary smiths decide which yasurimi to adopt themselves. Many follow the conventions of their master's school, though some smiths have established their own yasurimi patterns.

Yasurimi also function as the smith's personal "signature." By consistently adopting the same pattern over many years, the smith's yasurimi pattern becomes an individual identification marker in authentication. Though rare in modern times, there are cases where the subtle differences between a student's and master's yasurimi are used to determine lineage.

When purchasing a sword, whether the nakago is ubu or has undergone suri-age is one piece of information useful for understanding the sword's provenance and value. If you have questions about the yasurimi condition or nakago finishing, you can deepen your understanding by checking the NBTHK authentication certificate or inquiring with the seller.

In the authentication of Japanese swords, yasurimi is one of the "four elements of comprehensive judgment" alongside mei, jigane, and hamon. As a craftsman's cipher hidden in an unseen place, it continues to serve as an important clue in sword research today.