Mikawa Shiro Nagura 11.8oz. (330.4g) Japanese Natural Sharpening Stone
Approximately 115-130mmx80-90mmx20mm
I am not sure which layer of Mikawa shiro nagura, but it looks medium-high to lower side of the fine grit. It look finer class in Mikawa shiro nagura.
Hardness-------------8.2
It raises great amount of light black color slurry quickly.
(Scale; 1 to 10, 1-3 is very soft muddy rough grit whetstone 3-6 is soft medium grit whetstone, 6-8 is hard medium grit whetstone; 8-10 is fine grit whetstone)
Particle Size----------8.2
It makes my blue II steel kasumi blade knife Hagane became bright silver color finish. Jigae became frosted silver color finish.
(Scale; 1 to 10, 1-3 give deep scratch marks to the steel, 3-5 is delete the 1-3 scratches, 5-8 makes the steel cloudy, 8-10 makes the steel semi-mirror finish or mirror finish)
According to Dr. Kuniichi Tawara who is a Metallurgy doctor, and very famous Japanese sword researcher, Koma molecule is 10 to 20 micron. It might be like Tenjyo and Mejiro and Koma class grit. It should be good for right before starting the fine grit sharpening.
For razor sharpening, it is used one before the process sharpening by fine grit whetstone like Nakayama, Ozuku, Wakasa, etc.