From Japan · Updated 2026-07-03
How Japanese synthetic stones are actually made
Suehiro publishes its real production process. Bond chemistry — like the magnesia bond in Naniwa's Pro line — explains a lot of sharpening behavior you've felt but couldn't name.
Suehiro's six steps
Suehiro, a dedicated whetstone maker in Niigata City, documents its production as six steps: mixing and stirring the raw materials, press molding, drying, firing, final shaping, and quality checking. Abrasive grain, bond, and firing together determine how a stone behaves — how fast it cuts, how it wears, whether it loads up.
Their stated position is worth knowing when the eternal synthetic-vs-natural debate comes up: for coarse and medium work, they argue synthetics win on price, consistency, and usability, while naturals keep their appeal for finishing and aesthetics.
Why the bond matters: the Chosera example
Naniwa's Professional line — still known overseas by its old name Chosera — uses a magnesia bond. That bond is the reason for its fast, fine-feeling cut, and also the reason the usual advice is splash water on it rather than soaking it for long periods.
Shapton takes a different route: its Kuromaku ceramic stones, fired in Mashiko (Tochigi), are designed as splash-and-go from the start, with the grit encoded in the lid color.
Sources: ナニワ研磨工業 (Naniwa Abrasive, official) · シャプトン (Shapton, official)
These summaries extract facts from Japanese primary sources and rewrite them in our own words, with attribution. For the full detail (and the original nuance), follow the source links — they deserve the traffic.