Unknown Sunashi Suita Fine Grit Japanese Natural Sharpening Stone 2lbs. 9oz. (1160g)
I think that it is old days excellent large stone that is hard to come by nowadays.
#4000 to #6000 for final sharpening razor blade or fine finish (finest grit) high carbon blade
It is from used market, but it is in excellent condition, and I do not know which mine it derived from. It looks there are no layers on the side of the whetstone, so it is Sunashi Suita which is top rank class suita. It does not have layers, so it is less possibility to get unwanted particles coming up on the sharpening surface and it should be smooth stone all the way. It has some renge pattern too. I guess it might be Ohira, or Okunomon, or Okudo , or etc. one of the east side of the mine in Kyoto.
It produces very good amount of black slurry. It is sticky black color very nice slurry. It looks that it might 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)
It makes my white II steel Hon kasumi blade knife Hagane became from little frosted silver color finish. and Jigae became frosted silver color finish. It looks typical great suita that is cut fast and it make very nice Jigane and Hagane colors. I always look for suita like this one.
(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)
Probably #4000 to #6000 grit with the same as artificial whetstone. 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.