Hazuya and Nugui: The Sword Polisher's Final Finishing Techniques

Two-Stage Structure of Japanese Sword Polishing

Japanese sword polishing is broadly divided into two stages: "undercoat polishing (shitaji-togi)" and "finishing polishing (cosmetic polishing/keshō-togi)." Undercoat polishing is the process of refining the blade's form, removing rust and scratches, and precisely revealing the flat surfaces of each part such as the shinogi ridge, flat, spine, and yokote. Finishing polishing is the process of further polishing the surfaces refined during undercoat polishing and bringing out the activity of the steel (skin/jigane) and the details of the blade pattern (nie, nioi, gold lines, and lightning patterns) to a state suitable for appreciation.

In the work of the togishi (polisher), undercoat polishing is evaluated primarily on technical precision (geometric accuracy of surfaces), whereas finishing polishing is a "technique of presentation" to maximize the expression of the sword's individuality, where the polisher's aesthetic sense and experience become critically important.

Types of Whetstones Used in Undercoat Polishing

Polishing proceeds sequentially from coarse whetstones to fine whetstones. The typical order of use is as follows.

Ara-to (coarse whetstone): Equivalent to 80–120 grit. Used for removing rust, scratches, and marks from previous polishing. Blade shape correction is also performed at this stage.

Naka-to (medium whetstone): Equivalent to 240–400 grit. Removes marks from coarse polishing while improving flatness.

Koma-to (fine whetstone): Equivalent to 600–1000 grit. The stage where the ridge and flat surfaces become refined.

Uchigumo-ri-do (inner-haze whetstone): The "Kyoto-produced uchigumo-ri-do" is considered the highest quality natural whetstone. The fine particles on its surface create a uniform haze finish, allowing the pattern of the steel (jigane) to become visible. Used in the step immediately before finishing polishing.

Core Processes of Finishing Polishing

Uchi-gumori (Haze Finish)

The process of carefully polishing the steel (flat, ridge area, and spine) using a "wipe-paper whetstone (nuguigami-do)"—thin fragments of uchigumo-ri-do affixed to paper (shoji or washi). This results in the steel taking on a uniform haze finish, allowing the structure of the steel skin (itame, masame, and mokume patterns) to emerge and become visible for appreciation.

The difficulty of uchi-gumori lies in fine-tuning pressure and speed. Excessive force creates uneven haze, while insufficient force fails to transfer enough particles from the uchigumo-ri-do. The polisher adjusts finely for each area by sensing feedback through the fingertips and observing changes in the blade's reflected light.

Hatori (Edge Refinement) and Ha-dzuya (Edge Luster Whetstone)

Edge refinement (hatori) is the process of making the blade pattern (ha-yori) from the base of the blade to the kissaki stand out. In hatori, in contrast to the haze finish of the steel, the nie, nioi, gold lines, and sunamashi (sand-flow patterns) of the blade are finished in a bright, lustrous state.

The whetstone used is a small-fragment natural whetstone called the "ha-dzuya" (edge luster stone), used selectively to polish only the edge. Unlike ordinary whetstones, the ha-dzuya has extremely uniform particles and high hardness. It is distinguished by origin—such as "Tsushima-produced" (Tsushu-san) and "Tanba-produced" (Tanba-san)—and chosen according to the nature of the blade pattern (whether nie or nioi type).

Through hatori, a contrast emerges between the "haze" of the steel and the "light" of the blade pattern, which becomes the essence of the appreciative beauty unique to the Japanese sword. A Heian-period courtier's poem stating "The sword takes haze on the steel and light on the edge" refers to this aesthetic contrast.

Yubi-kaki / Nuguai (Finger Polishing)

As the final step of finishing polishing, there is "finger polishing (nuguai)"—using the polisher's nails or fingertips to make final adjustments to the junctions of the spine, ridge, and flat (ridge line and spine corners). This technique, which uses the polisher's own body as the abrasive without relying on whetstones, is the final adjustment step that removes minute surface irregularities and polishing inconsistencies.

Besides nails, some polishers use thin slices of an extremely fine-grained natural stone called "hadado" (skin stone), affixed to the fingertips, for finger polishing. The final uniformity of the surface depends on the precision of this step.

Logic of Whetstone Selection

The selection of whetstones for finishing polishing varies according to the sword's style, the nature of the steel, and the type of blade pattern.

Nie-deki (nie-made) blades (Soshu-den and late-old-sword styles): To make the large nie particles stand out, a somewhat softer ha-dzuya with coarser particles is effective. Overly hard whetstones risk flattening the nie.

Nioi-deki (nioi-made) blades (Bizen-den and Yamashiro-den): To preserve the fine nioi particles, uniform and fine-grained uchigumo-ri-do and ha-dzuya are used. Excessive polishing risks losing the depth of the nioi.

Steel skin patterns (itame, masame, mokume): Old swords with broadly exposed itame tend to have the pattern emphasized by uneven haze finishing. Yamashiro-den blades with flowing masame require uniform haze finishing, where the quality of uniformly-grained uchigumo-ri-do becomes critical to the evaluation.

Qualifications of Polishers and Modern Training

To become a togishi (sword polisher), organizations such as the "Association for Preserving the Techniques of Master Sword Polishers and Craftsmen (Bitō-kai)" and the "All Japan Sword Polishers Association" conduct practical examinations to certify the technical skills of togishi. The apprenticeship period is typically five years or more, and it is said to take nearly ten years from becoming a disciple of a master until one can perform all processes independently.

The number of modern togishi is estimated at around 200, of which those skilled enough to handle finishing polishing are even fewer. Polishing a single sword from start to finish takes 2–4 weeks, with costs typically ranging from approximately ¥100,000 to ¥600,000 depending on condition, blade length, and difficulty. While demand for polishing has increased with the vitalization of the sword market, an absolute shortage of skilled polishers remains a challenge for the entire industry.