Japanese Sword Polishing Stones: Types and Origins — From Arato to Uchigumori and Narutaki, the World of Natural Whetstones

The Whetstone (toishi) — Foundation of Japanese Sword Polishing

The skills of the polisher (togishi) in bringing a Japanese sword to a brilliant finish are often discussed. However, few realize that these skills are supported by numerous whetstones (toishi) of varying grades. Polishing is a sequential, multi-stage process that proceeds from coarse whetstones to fine ones, and the choice of whetstone appropriate to each stage determines the final result.

Here we explore the main types of whetstones used in sword polishing and their respective roles.

Whetstones for Foundation Polishing — From Coarse to Medium

Polishing divides into two main phases: foundation polishing (shitaji togi) and finish polishing (shiage togi). Foundation polishing shapes the blade and removes existing damage.

The first whetstone employed is the coarse arato (荒砥), which removes major irregularities and marks from previous polishing, establishing the blade's basic shape (sugata). One then progresses to somewhat finer whetstones such as bensuido (備水砥) and kaisei-to (改正砥), erasing the scratches left by the arato. Advancing further to medium nagura (中名倉) and fine nagura (細名倉), one progressively refines the scratch pattern while preparing the surface texture (hada).

Each stage of foundation polishing replaces the coarser scratches left by the previous whetstone with finer ones. Skipping even a single stage leaves prior scratches, which cannot be rectified later.

The Heart of Finish Polishing — Uchigumo-to

Once foundation polishing is complete, one enters finish polishing, which reveals the blade's tamahagane (steel structure) and hamon (edge pattern). The central role here is played by uchigumo-to (内曇砥).

Uchigumo-to is a finely-grained natural whetstone quarried in areas around Kyoto, which polishes the blade to a lustrous, settled surface. Uchigumo-to comes in grades suited to either hadzu-ya (刃艶) (edge luster) or jizu-ya (地艶) (surface luster), and the togishi distinguishes between them in use. Through polishing with uchigumo-to, the forging patterns of the tamahagane and the activity of the hamon become visibly apparent for the first time.

Edge Luster and Surface Luster — Polishing with Thin Whetstone Shards

In the final finish stage, thin shards of whetstone backed with Japanese paper are used, called hadzu-ya (刃艶) and jizu-ya (地艶). These are applied by finger directly to the blade, polishing the hamon area and the surface area separately. The hadzu-ya brings whiteness and brightness to the hamon, while the jizu-ya deepens the tamahagane to a bluish, subdued tone.

Thus the whetstones used in finishing are not employed as monolithic stones but transformed into delicate implements, manipulated by fingertip. The quality of the whetstone itself profoundly affects the final appearance of the blade.

Whetstone and Water — The Polishing Environment

Whetstones are always used with water. Water both dissipates frictional heat and maintains the polishing slurry (toishi-doro) between the blade and whetstone. The slurry itself contributes to the polishing action; the togishi constantly monitors its consistency and feel, making fine adjustments to pressure and blade angle.

Additionally, whetstones wear concave in the center with repeated use, so maintenance to preserve a flat working surface is essential. If one polishes with a warped surface, the blade's own surface geometry becomes compromised. In the polishing space, everything affects the final result — the position of the whetstone, the togishi's posture, all of it. Today, many togishi use man-made whetstones with consistent quality for portions of the foundation work, yet natural whetstones remain central to all finish polishing after the uchigumo stage.

The Pitfall of Skipped Stages

The most critical error in polishing is proceeding to finish work while foundation scratches remain. Finish whetstones lack the power to remove deep scratches; if prior scratch marks are discovered at the uchigumo stage, one must backtrack substantially and restart.

It must not be forgotten that polishing removes steel from the blade, albeit gradually. With each polishing, the blade loses metal and can never be restored. Therefore, deciding "how much to polish" and "what not to polish" are themselves crucial aspects of whetstone mastery. In preserving antique blades in sound condition for future generations, the polishing plan itself is directly linked to cultural heritage protection decisions.

Polishing Checkpoints for the Appreciator

When examining a blade in hand or in photographs, paying attention to the polishing condition transforms one's perception.

• Hike: Fine linear scratches visible when held to light; usually shallow marks acquired during handling or viewing
• Togi-geri (polish wear): Has the blade thinned from repeated polishing over years? Observe whether the yokote or shinogi lines remain crisp
• Contrast between tamahagane and hamon: Does the tamahagane settle into a subdued tone while the hamon gleams white? Beautiful, balanced contrast indicates thorough finish polishing

With these perspectives, the craftsmanship of each togishi and whetstone becomes distinctly visible.

Natural Whetstones as Finite Resources

Natural whetstones suitable for sword polishing, especially finish whetstones like uchigumo-to, are precious resources quarried in only specific locations. Fine whetstone production is limited, making the sourcing of superior stones as critical to the togishi as their technical skill. In recent years, depletion of natural whetstone deposits has been noted, and their value continues to rise.

Understanding Polish through the Whetstone

The togishi's mastery lies in selecting and mastering the correct whetstones in the correct sequence. Shaping with arato, building texture with medium stones, revealing tamahagane and hamon with uchigumo-to and the luster stones—this entire sequence succeeds only through the coordinated use of whetstones of differing natures.

When admiring a polished blade's clear tamahagane and brilliant hamon, remember the many whetstones that labored behind the scenes and the practiced eye of the togishi who selected them.

Understanding Sword Craftsmanship

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