A very hard iromono tomae in a light buff color which provides a slurry that is a combination of yellow and a touch of pink. The stone is grit rich and a slurry made with a diamond plate is crisp and very fast cutting and will easily hone up a razor to shave ready in just a few minutes or sharpen a plane blade to that same sharpness with little effort. To preserve the stamps I have regulated my testing to that portion just above the inventory #23 which also included that filled inclusion. The inclusion I found to be totally benign, does not affect a blade in one way or the other and leaves no errant scratches. I have however priced the stone at a lower grade to acknowledge this cosmetic defect and the crushed corner at the opposite end of the stone.
The ink stamps on this stone read from the top right down in kanji:
JUN SHO SHIN HON YAMA (true pur original mountain), below that in smaller sized kanji:
SAI KO KYU (very best quality)
The number 23 appears on the top, an inventory notation.
One end is ink stamped:
23 and MARUKA (Kato family logo)
I have also tested this stone with a Mikawa nagura koma and botan slurry, the test results were the the slurry was made mostly from the Mikawa nagura but that the Nakayama also provided slurry to.
Of course some of this will depend on the individual Mikawa nagura that you have, but I found that the base stone, the Nakayama is hard enough and it did resist releasing slurry in a normal manner of which I would have expected.
In general a 80%nagura/20%honyama mix.
H Level 9 is hard and requires concerted pressure
When using a diamond plate (DP) to lap or make a slurry the action is easy and fast.
flatten and seep into the stones surface, within five minutes the drop will be gone.
A drop of water placed with a finger tip will sit proud for one minute and then begin to
H Level 6-8 is medium hard and these stones will self slurry under a blade with pressure.
H or Hardness Scale Explanation.
Particle Size 9+++/5+++
Speed/Cutting 8+ to 9+++withslurry
Size in mm 202-76-35mm