Vintage Uchigumori 1lb.9.9 oz. (734g) Natural Sharpening Stone
196mmX67mmX22mm
#4000 for entry class in the fine grit for high carbon or stainless steel blade
It looks used vintage fine grit stone.
I am not an original owner, and I got it used market.
I do not know which mine derived from, but it has lots of renge red spots on the sharpening surface, and lots of tiny layers on the side of the faces, and it makes frosted blade after sharpening on Jigane and Hagane, so it looks typical Uchigumori to me.
Hardness-------------8.2
It raises great amount of black color slurry quickly.
It is soft side stone in the fine grit.
It does not need tomo nagura or the device to produce 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----------8.2
It makes my blue 2 carbon steel blade Hagane became frosted semi-mirror finish.
Jigae became very nice silver frosted color finish.
It might be great stone to finish Jigane or Damascus pattern.
(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)
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.