What does "Koppa" written under the natural whetstone size mean?
When trying to check the dimensions of the natural whetstone, an unfamiliar label "Koppa" is written instead of standard specifications, making one wonder what size it is. Because of the notice that the actual item may look completely different from the photos, it is difficult to determine what shape of product will be received.
Koppa refers to an irregular whetstone trimmed directly from natural raw stone pieces without being cut into standardized rectangular blocks.
Unlike standard whetstones with uniform width and length specifications, Koppa refers to an irregularly shaped whetstone crafted directly by preserving irregular fragments split from the raw stone. Because the original contours of the raw stone are left intact rather than cut down into straight rectangles, there are no fixed numerical dimensions.
HITOHIRA's whetstones are natural stones mined from the Ohira mine in Kyoto, Japan[1][2][3], and their size specification is classified precisely as this Koppa[4]. Unlike synthetic whetstones that are artificially molded and pressed into uniform shapes, they are split along the grain of rocks mined from nature, so their thickness, surface area, and even edge shapes vary from one another. This is why the product photos are presented merely as examples, and notice is given that the appearance of the whetstone actually received may be completely different from the photo[5].
The approximate weight range or minimum surface area criteria for Koppa-sized whetstones have not yet been confirmed in official materials.