This is a rare natural finishing whetstone from the Nakayama Inoshiriguchi line of Umegahata, Kyoto, classified as Hon Suita Daigokujo.

Inoshiri is located adjacent to the Nakayama mine and is believed to belong to the high-quality whetstone vein extending from Nakayama and Kita-Nakayama toward Beniyama. Stones distributed under the names “Inoshiriguchi” or “Nakayama Inoshiri” are rarely encountered. Since very few detailed mining records have survived, they are now regarded as particularly scarce natural whetstones.

This piece is a genuine Hon Suita, quarried from the Suita stratum. It contains fine, high-quality abrasive particles and responds readily when a blade is applied. While providing the effective cutting power characteristic of Suita stones, it also offers excellent particle breakdown. The stone engages the blade firmly at the beginning, after which the slurry gradually becomes finer as sharpening progresses. Its ability to combine strong abrasive performance with a highly refined finish is one of its greatest qualities.

This stone is also classified as “Daigokujo,” one of the highest quality grades. This designation was reserved for exceptional stones selected through an overall assessment of their stone quality, density, fineness of abrasive particles, and sharpening performance. Its Daigokujo classification indicates that this piece was recognized and carefully selected as a particularly fine Hon Suita from the Inoshiriguchi line.

It provides clear tactile feedback, making it easy to monitor the blade’s condition and perform precise edge refinement. It produces a keen, finely developed edge on the steel while bringing out an elegant kasumi finish with a subtle luster on the softer cladding. It is therefore well suited to those seeking not only excellent cutting performance but also a beautiful overall blade finish.

The sharpening surface displays a beautiful contrast of white and beige. However, the difference in color does not affect its sharpening characteristics: the stone remains uniform across the entire surface and provides a consistently smooth and pleasant sharpening experience.

Combining practical performance with historical interest, this rare natural finishing stone is highly recommended for kitchen knives, straight razors, planes, chisels, and other fine-edged tools.