Please check the photos. This is an Ohira Uchigumori Renge, a traditional Japanese natural polishing whetstone originating from Kyoto, Japan. It is particularly suitable for Hato (blade surface) polishing of Japanese swords, and high-quality specimens of this type have become increasingly difficult to obtain in recent years.

This particular stone was purchased directly from the Ohira quarry source, providing a clear and reliable provenance. In addition to its practical polishing capabilities, it also holds historical and collectible value as an authentic example of Kyoto's traditional natural whetstone heritage.

Ohira Uchigumori stones have long been used in the traditional polishing process of Japanese swords. In particular, during Hato polishing, they help produce a natural, subdued silvery-white appearance on the blade surface, enhancing the distinctive texture and character of the steel.

One of the most notable characteristics of this specimen is its moderate hardness and its ability to produce an exceptionally fine, uniform slurry almost immediately upon contact with the blade.

The stone has an estimated hardness rating of approximately 4.0− on our in-house scale. It is neither excessively hard nor overly dense, providing natural, smooth contact with the blade and a comfortable, controlled polishing sensation.

During test sharpening, a fine slurry began forming almost immediately after the blade was placed against the sharpening surface and moved. Slurry production was exceptionally quick, and as polishing continued, a consistent and uniform slurry developed steadily across the surface. This allows the stone to deliver excellent abrasive performance from the very beginning of the polishing process.

Another important advantage of this specimen is its excellent polishing ability. The fine abrasive particles act evenly across the blade surface, allowing for controlled material removal while producing a delicate and consistent finish.

After polishing, the blade develops the characteristic soft, muted silvery-white appearance associated with traditional Uchigumori stones. Rather than producing the strong reflections of a mirror polish, it creates an elegant, naturally subdued finish that gently diffuses light and enhances the appearance of the steel.

In addition to traditional Hato polishing, the stone can also be cut into smaller pieces and shaped according to the intended application, making it potentially suitable for detailed polishing and various other stages of traditional Japanese sword finishing.

The natural appearance of this Ohira Uchigumori Renge is another of its distinctive attractions.

The sharpening surface displays a beautiful combination of pale bluish-gray and grayish-purple tones, overlaid with intricate yellowish-brown to golden patterns. Fine reddish-brown and reddish-purple speckles can also be observed in certain areas, creating the rich natural coloration characteristic of Renge whetstones.

These patterns were formed naturally over an immense geological timescale, giving each Ohira Uchigumori stone its own individual appearance. This particular specimen is especially attractive for the way its soft grayish-purple background blends with warm yellowish-brown markings, creating a distinctive and visually appealing natural pattern.

 Please note that these are not for beginner sharpeners since they're harder to use.These are natural stones meaning that every single one of them are different so my measured size are not accurate. This is a life time investment for people who lives sharpening their knives and tools, do not hesitate to ask me your questions.”

Dimension : 

55-72m×197-205mm×23mm / 839g ( Approx.) 

 - Grit size: Fine 6000