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

Nakago and Yasuri-me — Why Cryptographic Codes Are Engraved Inside the Handle

The nakago of a Japanese sword is normally hidden inside the tsuka (handle) and is not visible during viewing. However, this nakago is precisely the "most critical part that proves the sword's provenance," and together with the mei (maker's signature), nenki (date), and tameshikiri-mei (test-cut signature), the yasuri-me (file marks) applied to the surface of the nakago become the deciding factor in authentication.

Yasuri-me are the patterns of scratches left behind when the surface of the nakago is finished by scraping with a metal tool called a yasuri (file) after the nakago has been shaped. Functionally, this serves the purpose of preventing corrosion and improving adhesion to the handle, but because each school and each era used nearly fixed patterns, "which yasuri-me" functions as an authentication indicator of the school and era.

Major Types of Yasuri-me

Kiri-yasuri (Cross-filed marks): File marks that run roughly perpendicular (90 degrees) to the long axis of the nakago, the most basic form. Frequently seen in old swords of the Bizen and Yamashiro traditions. Detailed classification is based on whether the horizontal lines are perfectly aligned at right angles or slightly diagonal.

Suji-yasuri (Lined marks): File marks that run parallel or at an acute angle to the long axis of the nakago, with a pattern of vertical streaks. Frequently used by swordsmiths of the Yamato tradition and serves as an authentication indicator for old Yamato swords from the Kotou period.

Katte-sagari (Right-handed descent): A pattern of file lines running diagonally downward toward the edge side (viewed from the left side of the nakago). Frequently seen in shin-to and shin-shin-to (new and newer swords) from the Edo period onward, and particularly adopted as a basic form by many Edo-period swordsmiths.

Gyaku-katte (Left-handed descent): The reverse direction of katte-sagari — file marks running diagonally downward toward the ridge side of the nakago. In some cases, it becomes an authentication indicator when a particular school adopted this pattern.

Oosuji-chigai (Large diagonal streaks): File marks engraved at a large angle (45 degrees or more), sometimes creating a visually prominent large cross-hatch pattern.

Keshou-yasuri (Decorative filing): A decorative finish where file marks are applied finely and regularly to make the nakago surface appear beautiful. More often applied by skilled craftsmen from the late Edo period onward to showcase their technical skill.

Historical Transitions of Yasuri-me — From Kotou to Shin-shin-to

The patterns of yasuri-me changed over time and are used as supplementary indicators for era authentication.

Kotou period (to ca. 1596): Kiri-yasuri was the basic form. Master swordsmiths of the Bizen and Yamashiro traditions used relatively fine kiri-yasuri, while the Yamato tradition frequently employed suji-yasuri. In many cases the nakago is short and corroded, making the yasuri-me difficult to read.

Shinto period (1596–ca. 1764): Katte-sagari became mainstream. Edo-period swordsmiths adopted relatively uniform katte-sagari, while Osaka-period swordsmiths often distinguished themselves by exceptionally fine finishing.

Shin-shin-to period (1764–1876): Keshou-yasuri became more common, and there is a tendency for the finishing precision of the nakago surface to increase. Representative shin-shin-to swordsmiths such as Suishinshi Masahide and Minamoto no Kiyomaro carefully finished the nakago as part of their work.

Yasuri-me Application in Sword Authentication — How to Detect Later Alterations

Yasuri-me are also an effective indicator for detecting false mei (forged signatures) and alterations. During the Edo and Meiji periods, when the value of old swords soared, practices such as "suriage-mei" (erasure signatures) — where a nakago's existing signature was scraped away and replaced with a different one — and cutting new signatures onto unsigned blades became rampant.

Such alterations often create contradictions in the yasuri-me in the following ways:

• The pattern of yasuri-me changes only around the signature (traces of scraping with a different file)
• The direction of the yasuri-me does not match the era or school
• Old yasuri-me are hidden beneath the newly cut signature (observable under fluorescent light or magnification)

In authentication reviews by the Japan Art Sword Preservation Society (NBTHK), confirmation of yasuri-me is a mandatory step in the authentication workflow, and in cases of doubt, oblique-light photography of the nakago and microscopic observation are performed.

Modern Swordsmith's Yasuri-me Selection — Tradition and Individual Expression

When creating a sword, modern swordsmiths themselves decide which yasuri-me to employ. Most often they follow the customs of their master's school, but some swordsmiths have established their own unique yasuri-me patterns.

Yasuri-me also functions as the swordsmith's own "signature." By consistently adopting a particular pattern over many years, a swordsmith's yasuri-me pattern becomes an individual identification indicator in authentication. Though rare in modern times, there are cases where the subtle differences between a disciple's yasuri-me and their master's are used to determine lineage.

In Japanese sword authentication, yasuri-me is one of the "four elements of comprehensive judgment" alongside mei, jigane (steel grain), and hamon (temper pattern), and continues today as an important clue in sword research as a craftsman's code hidden in an invisible part.