This is a natural finishing stone from the Nakayama Kurumaguchi line.

Kurumaguchi is recognized as one of the most highly esteemed mining entrances within the Nakayama mine and has long been renowned for producing stones ideally suited to delicate, high-precision finishing work on straight razors, Japanese woodworking tools, and honyaki knives. While stones quarried from the central section of the tunnel are generally regarded as the finest, this particular stone was quarried from the Hachimai layer located on the outer side of the Kurumaguchi tunnel.

The reverse side reveals what appears to be a softer Karasu layer. Although the stone has not been flattened on that side, it offers the unique opportunity to enjoy sharpening on both the front and reverse surfaces.

Although it exhibits subtle characteristics associated with the Hachimai layer, the stone remains exceptionally dense and fully retains the refined sharpening qualities for which Kurumaguchi stones are celebrated. It offers excellent edge engagement and outstanding tactile feedback, allowing the user to maintain precise control throughout the sharpening process.

Water absorption is moderate, and the stone naturally generates a fine, easily managed slurry during sharpening, making it possible to produce an exceptionally keen and highly refined cutting edge.

The finished edge combines exceptional sharpness with an elegant, highly polished finish, offering an outstanding balance between cutting performance and aesthetic refinement. It is particularly well suited for straight razors and blades made from high-hardness steels.

Despite its subtle Aisa influence, this stone faithfully preserves the elegant sharpening character that has made Nakayama Kurumaguchi stones so highly respected among natural whetstone enthusiasts. It is an excellent example of the distinctive qualities that have earned Kurumaguchi its outstanding reputation.

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  tools, do not hesitate to ask me your questions.”