Tsushima Kuro Nagura Medium to Medium-High Grit approximately 4lb. 11.5oz. (2138g) Japanese Natural Sharpening Stone
****the pictures or video is not actual image, but it is very similar with the pictures. The size and weight are not also the actual size and weight, but it should be very similar too. The hardness and particle size should be similar too*****
It produces good enough amount of dark gray slurry quickly, and it is not too much amount of slurry. It is just moderate amount of slurry. It is not thick sticky slurry. (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---------- 7.6
My blue II steel blade knife Jigane became cloudy light gray silver color with fine whetstone marks lines-up on Jigane, and Hagane became little bright silver color with very fine whetstone marks lines-up. (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) Kuro nagura is one process before fine grit hone sharpening starting, or two processes before using Nakayama or finest class finest grit whetstone. After used the fine grit whetstone like Nakayama whetstone for a long time, the razor or the fine finished blade gets dull, and then the blade of edge needs little rougher whetstone with sharpening.
Kuro Nagura whetstone is needed in the situation.
Kuro Nagura is also for; Super hard whetstone to make it easier to sharpen, and it makes to increase whet power by taking out stuck residue or unwanted molecules on the surface of whetstone, and removing dull shaped whetstone molecules, and getting new layers of sharp cornered the whetstone molecules.