Please see more detail the video below:
Unknown Fine Grit Japanese Natural Sharpening Stone 2lb. 14oz.
212mmx74mmx38mm
It is used an old Japanese natural fine grit sharpening stone.
Hardness-------------8.6
It raises very good amount of black slurry quickly.
It looks it does not need tomo nagura or the device to raise the slurry (worn Diamond lapping stone).
(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----------8.9
It makes my blue II steel kasumi blade knife Jigane became light silver color to light color silver finish, and Hagane became from semi-mirror finish to mirror finish.
It is not too hard and not too soft stone.
(Scale; 1 to 10, 1-3 give deep scratch marks to the steel, 3-5 is delete the 1-3 scratches, 5-8 makes 3the steel cloudy, 8-10 makes the steel semi-mirror finish or mirror finish)
Natural whetstone has wider capacity than artificial whetstone, and actually, we do not know until sharpen blade on the hone for a while. Because artificial whetstone molecules do not break down to smaller sizes, but Natural whetstone molecules are possible to break down to smaller sizes, and those molecules are mixed with sharpened steel molecules, and make Jigane as suitable Jigane color, and Hagane as suitable Hagane color. It is natural mystics.