This is a rare set of natural whetstone koppa intended for making Hazuya and Jizuya finger stones used in traditional Japanese sword polishing. The set combines an Ōhira Renge Uchigumori stone with a yellow Nakayama finishing stone, allowing the polisher to enhance the distinct characteristics of both the hardened edge and the jigane during the delicate final stages of polishing.

The bluish stone on the left is an Ōhira Renge Uchigumori from Kyoto. Featuring beautiful renge patterns, it is intended to be processed into Hazuya. Its fine abrasive particles produce a pale, subdued, and softly lustrous silver-white finish rather than a strong mirror-like shine. The gentle haze characteristic of Uchigumori gives the blade an elegant appearance while naturally enhancing the hamon and its subtle activities.

The yellow stone on the right is a natural finishing stone from Nakayama, Kyoto, intended for making Jizuya. In the field of Japanese sword polishing, finishing stones used for Jizuya are sometimes collectively referred to as “Narutaki.” Strictly speaking, however, Narutaki is a general geographical name for an area in eastern Kyoto and does not identify the specific mine from which a stone was quarried.

Nakayama Jizuya is used to emphasize the jihada visible in the sword’s jigane, beautifully revealing the grain patterns and delicate characteristics created through the forging process. It gives the steel a natural luster and visual depth while helping to define the distinctive qualities of itame-hada, mokume-hada, masame-hada, and other grain structures.

To prepare these stones as Hazuya and Jizuya, split each koppa into pieces of a suitable size and thickness, flatten the polishing surface, and round the corners. Yoshino paper may then be attached to the reverse side with urushi lacquer to prepare the pieces for traditional sword polishing. As these are natural stones, we recommend testing and carefully inspecting each piece during preparation to ensure that it contains no hard particles or areas that could cause scratches.

This set allows the user to enjoy both the pale, softly lustrous silver-white finish produced by Ōhira Renge Uchigumori Hazuya and the depth and definition that Nakayama Jizuya brings to the sword’s jihada. Offering the ability to delicately refine both the hardened edge and the body of the blade, this is a rare and highly practical set of natural koppa for traditional Japanese sword polishing.