Unknown Mine Medium Grit Japanese Natural Sharpening Stone
Weight: 1578g (3lb. 7.7oz.)
Size: 200mm x 67mm x 50mm (7-7/8" x 2-3/4" x 2")
It is a very clean rectangular shape with an excellent thickness of 50mm, providing a long lifespan.
It looks around 1000 grit, medium grit stone, and it might be Shiro nagura, but not sure.
Hardness-------------8.7
It gets black slurry quickly, but it is not soft 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----------4.0
(Scale: 1-10 overview in referenced text)
My blue 2 steel kasumi blade became the soft iron sliver frosted and the steel became light frosted silver color.
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.