Japanese natural stones

Tennen toishi, graded by use not grit

Japanese naturals have no grit number and no single micron. Each grade band is a wide range. The fine end is anchored by direct SEM measurement (about 2 to 3 micron radiolarian silica in Kyoto finishers). Ranges, estimated, except where measured.

Each grade below shows its size in microns, its spread (the published distribution, where a maker or standard gives one; most makers publish none), and where that size lands on the reference scale, a shared yardstick for reading grit numbers across makers.

Particle sizemicrons, log

1005030201053210.5

coarserfiner

inkmeasured or standardmaker figureour estimate

shapeknown distributionpoint, spread unknown

荒砥 (arato, coarse)Our estimate

60 µm

Range 20 to 100 µm. Rough JIS-equivalent #150-#800 (sources spread: #150-800, #200-600, #500-1000).

spread 20 to 100 µm · reference scale about #230

中砥 (nakato, medium)Our estimate

13.5 µm

Range 2 to 25 µm. Rough JIS-equivalent #800-#5000.

spread 2 to 25 µm · reference scale about #830

合砥 / 仕上げ砥 (awasedo / shiageto, finishing)Our estimate

2.75 µm

Range 0.5 to 5 µm. The headline category (Nakayama, Ohira, Ozuku, Suita and the rest).

spread 0.5 to 5 µm · reference scale about #4350