This is a rare Uchigumori natural finishing stone fragment (koppa), Having Renge (Lotus ) patterns from Mizukihara, Kyoto. It is a fine-quality Uchigumori stone suitable for processing into Hazuya used in traditional Japanese sword polishing. High-quality Mizukihara Uchigumori has become increasingly difficult to obtain in recent years.

During polishing, the stone produces the fine, uniform slurry characteristic of Uchigumori. Its stable abrasive structure helps minimize unevenness across the polished surface, allowing the user to monitor the blade’s condition while working smoothly and precisely. Despite its manageable polishing feel, the stone offers excellent abrasive power and efficiently produces a delicate, refined finish.

After polishing, the blade acquires a pale, subdued, and softly lustrous silver-white appearance rather than a strong mirror-like shine. The gentle haze characteristic of Uchigumori gives the blade an elegant appearance, making the stone particularly suitable for delicate polishing work intended to enhance the jihada (steel grain) and hamon (temper line) of a Japanese sword.

To use the stone as Hazuya, the koppa is split into pieces of an appropriate size and thickness. Each piece is then flattened, its corners rounded, and Yoshino paper is attached to the reverse side with urushi lacquer. As this is a natural stone, we recommend carefully inspecting each piece during preparation to ensure that it contains no hard particles or areas that could cause scratches.

Combining practical value as a source material for Hazuya with the uniform haze, excellent polishing power, and pale, elegant silver-white finish characteristic of Mizukihara Uchigumori, this is an exceptionally rare and desirable vintage koppa.