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

The Two-Phase Structure of Japanese Sword Polishing — Preparatory and Finishing Polishing

Japanese sword polishing is divided into two major phases: "preparatory polishing" (shitaji-togi) and "finishing polishing" (shiage-togi). Preparatory polishing is coarse work that shapes the blade, removes scratches, and creates the foundation for polishing. Finishing polishing, by contrast, is a delicate final process that brings out the full beauty of the sword.

The "insertion polishing" (sashikomi-togi) and "finger polishing" (sashi-togi) techniques explained in this article are at the core of finishing polishing. These techniques represent a systematic approach to maximizing the two most important elements in sword appreciation — the brilliance of the hamon and the grain patterns of the jihada — and reveal both the skill and philosophy of the polisher.

What Is Insertion Polishing?

Insertion polishing is a technique in which an extremely fine whetstone is applied to the blade at a very shallow angle, as if being "inserted," to bring out the brilliance of the hamon. The whetstones used are natural stones such as the uchigumori-to or hatoriishi, with京都-produced uchigumori-to considered the highest quality.

The characteristic of insertion polishing lies in deliberately finishing the jihada and hamon with different polishing methods. Because the hamon (the boundary of the martensite microstructure formed by quenching) has a fundamentally different steel microstructure from the jihada (pearlite and ferrite structures), it responds differently even when polished with the same whetstone and pressure. Insertion polishing exploits this difference to selectively brighten only the hamon.

Specifically, an uchigumori-to is thinly and flatly shaped into "a fragment the size of a pinky nail," which is then applied to the blade at a very shallow angle (approximately 10-15 degrees). The "activity" of the hamon — the fine structural variations such as nie, nioi, kinsujи, and sunagashi — is visually emphasized through this polishing.

Finger Polishing (sashi-togi) — Bringing Out the Grain of the Jihada

While insertion polishing reveals the beauty of the hamon, finger polishing reveals the beauty of the jihada. In finger polishing, the polisher either attaches a thin whetstone fragment to their fingertip or carefully controls the whetstone with their fingertip to finish the surface of the jihada with extreme delicacy.

The jihada exhibits unique grain patterns created by forging methods: itame-hada, mokume-hada, masame-hada, and ayasugi-hada. These are formed by the steel's crystal microstructure created through forging, which becomes visible on the surface through polishing.

The mechanism by which finger polishing brings out the jihada's grain involves fine differences in hardness within the metal structure. The "flow" of board grain, wood grain, and similar patterns shows subtle differences in structural density, so applying uniform polishing creates surface irregularities. These fine irregularities scatter light, making the grain visible as a tangible texture.

Insertion polishing and finger polishing differ in both their targets and application methods. The content above can be summarized as follows:

Systematic Whetstone Use — A Gradual Progression from Coarse to Fine

Japanese sword polishing employs whetstones systematically, progressing through different grit levels. The typical polishing sequence is:

• Ara-to (coarse stone): Removes scratches and shapes the blade. The stone's grit is coarse and removes large amounts of metal.
• Naka-to (medium stone): An intermediate step that removes the marks left by the coarse stone.
• Uchigumori-to: The core of finishing polishing. Natural stones from Kyoto, particularly Kameoka, are highly prized (characteristics of whetstones by source region are compiled in this article).
• Hatoriishi: A small whetstone designed specifically for polishing the blade edge.

Whetstone polishing is completed at this stage. The subsequent "wiping" (nugui) is a separate finishing treatment from whetstone polishing. Iron oxide powder (kinkuro or tetsuiro) is mixed with clove oil or camellia oil and wiped over the hamon, giving the jihada a deep luster. Wiping involves no cutting and is positioned as an independent technique distinct from insertion polishing.

Of these, the uchigumori-to is a special stone that satisfies contradictory requirements: uniformly finishing the polishing surface with uniform fine grit while imparting brilliance without damaging the jihada's character. Kyoto stone excels because the region's whetstones possess the right balance of water retention and uniform grit, though the geological mechanism behind this remains a subject of ongoing research.

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

Understanding the philosophy of the polisher is crucial to discussing insertion polishing and finger polishing techniques: "We reveal the sword's inherent beauty rather than simply polishing it."

This philosophy runs deep. The polisher's work does not simply make the sword look better; rather, the essential beauty of the hamon, jihada, and curve of the sword becomes expressed in a form visible to the human eye. Excessive polishing flattens the jihada's grain and reduces the fine details of the hamon to uniformity. True skill is revealed not in "how much one polishes" but in "knowing when to stop."

This philosophy resonates with Buddhist aesthetics of wabi and sabi — the appreciation of incompleteness, empty space, and natural change. This sensibility of restraint flows through the polisher's philosophy of not over-polishing.

The Challenge of Rust Removal — The Ethics of Polishing

Among ethical challenges for the polisher, one of the most difficult is rust removal. Old swords often develop rust from long-term storage. While light rust can be removed through polishing, deep rust has already corroded the jihada, and attempting to remove it through polishing risks destroying the steel itself.

The ethical principle shared among contemporary polishers is: "With culturally significant swords, preserve the amount of steel material as much as possible." Rather than removing all rust to achieve perfect brilliance, respecting the old sword's komi — the deep coloration that rust creates — is considered the correct approach to sword preservation (this decision-making criteria is explored in more detail in this article).

Contemporary Polishing Challenges — The Depletion of Traditional Whetstones

The uchigumori-to, which determines the quality of insertion polishing and finger polishing, is a natural stone with limited mining capacity. The prime uchigumori-to deposits of Kyoto and Kameoka saw substantial extraction in the latter half of the twentieth century, and sourcing high-quality stones becomes increasingly difficult each year.

In response to this challenge, artificial stones (industrial products) continue to improve, but completely replicating the polishing characteristics of natural stone remains difficult. Among polishers, the inventory management of quality uchigumori-to has become a matter of survival, with stone sourcing linked to broader issues of polisher retirement and succession.

The two techniques of insertion polishing and finger polishing transcend mere craftsmanship to represent a philosophical practice of transmitting Japanese swords as cultural artifacts to the next generation "in a visible form." If the beauty of the sword is "the result of the swordsmith's work," then making that beauty visually manifest is "the true essence of the polisher's work."