Sashikomi and Sashi-Togi Polishing: The Sequential Use of Stones and the Togishi's Philosophy of 'Bringing the Blade to Life'

Two-Phase Structure of Japanese Sword Polishing — Foundation Polishing and Finish Polishing

Japanese sword polishing divides into two major phases: "foundation polishing" (shitaji-togi) and "finish polishing" (shiage-togi). Foundation polishing is coarse work that shapes the blade, removes scratches, and establishes the polishing foundation. Finish polishing is the delicate final stage that brings out the "beauty" of the sword to its fullest.

The "insertion polishing" (sashikomi-togi) and "finger polishing" (sashi-togi) explained in this article form the core of finish polishing work. These techniques comprise a systematic approach to maximizing the two most important elements in sword appreciation — the "radiance of the hamon" and the "skin texture (hadame) of the jihada" — and represent the stage where the polisher's skill and philosophy are most starkly evident.

What Is Insertion Polishing?

Insertion polishing is a technique in which an extremely fine whetstone is held at a very shallow angle to the blade surface, "inserted" as it were, to bring out the radiance of the hamon. The whetstones used are natural stones such as "uchigumo-to" (inner cloud stone) and "hatori-to" (edge-taking stone), with "Kyoto-produced uchigumo-to" considered the highest quality.

The characteristic of insertion polishing is that "the jihada and hamon are deliberately finished with different polishing methods." Because the hamon (the martensite crystalline boundary formed by hardening) and the jihada (pearlite and ferrite structures) have fundamentally different steel compositions, they react differently even when polished with the same stone and pressure. Insertion polishing exploits this difference to selectively brighten only the hamon section.

Specifically, an uchigumo-to is thinly shaved flat into "small pieces about the size of a pinky fingernail," then held at an extremely shallow angle (roughly 10–15 degrees) to the blade surface. The "work" (hataraki) of the hamon — the fine structural variations such as nie, nioi, kinsuji, and sunagashi — become visually emphasized through this polishing method.

Finger Polishing (Sashi-togi) — Making the Jihada's Skin Texture Rise

While insertion polishing brings out "the beauty of the hamon," "finger polishing" brings out "the beauty of the jihada." In finger polishing, the polisher either affixes a thin whetstone piece to the fingertips or controls the stone with the fingertips to finish the jihada surface with extreme delicacy.

The jihada bears distinctive skin patterns born from forging: "itame-hada" (board grain), "mokume-hada" (wood grain), "masame-hada" (straight grain), and "ayasugi-hada" (chevron grain). These emerge on the surface through polishing as the steel's crystalline structure formed during forging becomes visible.

The mechanism by which finger polishing makes the jihada's texture surface is rooted in fine hardness variations in the metal structure. The "flow" of board grain and wood grain patterns results in subtle density differences, so uniform polishing creates irregularities. These microscopic irregularities scatter light, making the skin texture visible as surface character.

Systematic Whetstone Progression — A Staged Approach from Coarse to Fine

Japanese sword polishing employs whetstones in systematic stages according to their grit. The general polishing sequence is:

Ara-to (coarse stone): Scratch removal and shape refinement. Large grit; high metal removal volume. Naka-to (medium stone): Intermediate step removing scratches from the coarse stone. Uchigumo-to (inner cloud stone): Core of finish polishing. Natural stones from Kyoto's Kameoka region are treasured. Hatori-to (edge-taking stone): Specialized small stone for polishing the edge specifically. NuguI (wiping): Final finish using oil and metal powder. Uses "wiping paper" rather than whetstones.

Of these, uchigumo-to is a special stone meeting contradictory demands: uniform fine particles evenly finish the polishing surface while giving luster without damaging the jihada's expression. The superiority of Kyoto production is attributed to that region's stones' moderate "water retention" and "particle uniformity," though the geological mechanism remains under study.

The Polisher's Philosophy — "Revealing" Rather Than "Polishing"

Understanding the polisher's philosophy — "not polishing the sword, but revealing the sword's inherent beauty" — is essential to discussing insertion polishing and finger polishing techniques.

This philosophy runs deep. When a polisher applies their craft, the sword doesn't simply "look better"; rather, the sword's essential aesthetic qualities — hamon, jihada, and curve — become visible to the human eye in expressed form. Over-polishing flattens the jihada's texture and planarizes the hamon's fine work. True skill lies not in "how much to polish" but in "where to stop."

This philosophy echoes Buddhist aesthetics of *wabi* and *sabi*. The sensibility that finds beauty in incompleteness, emptiness, and natural change flows through the polisher's aesthetic of "self-restraint in not over-polishing."

The Rust Removal Challenge — The Ethics of Polishing

Among ethical challenges for polishers, the particularly difficult question is "how to remove rust." Antique swords (koto) often develop rust from long storage. Light rust can be removed by polishing, but deep rust has corroded the jihada itself; removing it through polishing risks losing the steel material itself.

The "ethics of polishing" shared by contemporary polishers holds: "For swords of cultural heritage value, preserve the metal material as much as possible." Removing all rust to achieve perfect radiance is less correct than respecting the antique sword's inherent "old patina" (komi) — the deep, complex coloration rust imparts — in the context of sword cultural heritage preservation.

The Modern Polisher's Technical Challenge — Depletion of Traditional Whetstones

The uchigumo-to that determines the quality of insertion and finger polishing is a natural stone with limited extraction. The premium uchigumo-to ore veins of Kyoto's Kameoka region were substantially mined in the late 20th century, and obtaining quality stones becomes increasingly difficult year by year.

In response, improvements to synthetic stones (industrial products) continue, but completely replicating natural whetstone polishing characteristics remains challenging. Among polishers, managing inventory of quality uchigumo-to has become a matter of survival, with stone sourcing entangled in broader issues of polisher retirement and succession.

Insertion polishing and finger polishing, as techniques, transcend mere craftsmanship to become philosophical practice — "conveying Japanese sword cultural heritage to the next generation in visible form." If the sword's beauty is the "result of the sword-maker's work," then making that beauty visually manifest is the "essence of the polisher's work."