Artisans say that using natural whetstones enhances the sharpness, resulting in exceptionally long-lasting cutting tools. Whetstones from Kyoto are highly regarded by professionals due to their extremely fine texture and quality.

The abrasive grains of natural whetstones are typically rounded and about 2-3μm in size (synthetic grains are around 5μm). As the blade and the whetstone interact, the particles become smaller, eventually reaching ultra-fine particles akin to #15000 or finer baby powder. These particles contribute to the creation of an ultimate cutting edge.

When sharpening with natural whetstones, the blade edge generates heat to the point of burning, similar to the heat treatment of steel. While microscopic changes may not be visibly apparent, using a hardness tester confirms a definite increase in hardness. The mysterious hardening process, driven by the power of nature in natural whetstones, is a key factor in their popularity.

This unique hardening effect leads to prolonged sharpness, extending the lifespan of valuable cutting tools. It is recommended to use natural whetstones for the final sharpening of blades.

Unlike synthetic whetstones, natural whetstones do not have grit sizes. The fineness and hardness of the whetstone vary depending on the quarry. The place of origin serves as a general indicator.