Thread: Razor stone hardness, quality, abrasive speed and more.....

This was from the ''Kiita fan club'' thread. Better to start a new
thread on this matter:

Originally Posted by alx

Sharpman


I like Okudo stones, the good ones are very good and razor users seem to cherish them. But remember that each mine gave up all qualities of stone, some good, great and just average. So seeking out the really great stone is the challange. Great stone has a larger quantity per pound of grit as weighed against binder. More grit means faster cutting action.


For razors the size of the grit is important and although all the mines provided a certain amount of razor quality stone at one time or another, by far the greatest portion of razor (kamisori toishi) hone stone came from the few mines clustered around the Nakayama mine in the Umegahata valley. The reason for this is logical and scientifically proven, the finest of the wind blown (aeolian) material settled in this part of the Tamba Terrane during the original volcanic event that belched forth the materials that make up the sharpening stones as we know them. Logically the "closer to the source" and coarser material settled first in the area of the terrane that now is on the map as apparing farther to the west near Kameoka City or beyond, while the finest particles traveled farther while suspended in the easterly blown wind and settled closer and near to what is now thought of as Kyoto. Of course as you may know, the Original Event took place during the late Permian or Jurassic Periods while the infant hitch hiking Tamba Terrane form resided on the Pacific tetonic plate in the area of the globe now known as Hawaii. Evidently it took over 2,000,000 years to transport piggyback style to Japan as the Pacific Plate moved west while diving under the various Asian Plates.


So yes, Okudo are worth more than usual if you are comparring against the more remote mines to the west, and yes, some Okudo, if they are made up of super fine grit, are worth more than ususal when comparred to similarly priced but inferior stones.
Sorry for the long answer, which is about 1/3 of my first version, but it appears I have too much time on my hands. Alx

Thanks Alex, great answer!

Some more question if you don't mind. I don't get the chance to ask
an expert like yourself questions on tennen toishi everyday. What is the
ideal finishing stone for razors?

My guess:
- a rather hard to very hard stone,
- works quickly(high abrasive power)
- sheds superfine grit
- free of impurities

Could the ideal razor finishing hone also be ideal for plane blades? I sharpen
plane blades a lot and usually finish on the 8000 synthetic stone, but now also
use the chinese guangxi hone, which is finer. Razor guys go up to 30.000

Which strata produces the hardest and/or finest stones? I have
been following this forum for a few years now and it seems that people
here like asagi stone the most because they are the hardest and finest. Asagi
is from the tomae strata. I find this confusing as the suita strata is even deeper.
Shouldn't the deepest strata produce the hardest stones because all the weight
from above has/is compressed it?

A lot of people are using very hard stones with fine nagura slurry. I am
guessing they do this because otherwise the stone is too slow and the
sharpening process would take too long. I think another reason might be,
is that a super hard stone sheds its own abrasive super slowly which also
makes it possible for the nagura slurry to break down to superfine particles.
Which type of stone is/was preferred in Japan now and in the past, an extre-
mely hard stone, that almost doesn't release its grit and should be used with
nagura slurry, or a slightly less hard stone that releases very/super fine grit
without nagura slurry?

What makes certain finishing stones work very quickly while others are much slower?
Simple answer I could think about would be the abrasive concentration in the stone.

Where do the whetstone shops in Japan buy their stones? The only mountain still being
mined is maruoyama AFAIK, so where do the shops get their nakayama, ozuku, shoubudani
... stones from?

Thanks Alex in advance for answering.

Sharpman

Originally Posted by SharpMan

Where do the whetstone shops in Japan buy their stones? The only mountain still being
mined is maruoyama AFAIK, so where do the shops get their nakayama, ozuku, shoubudani
... stones from?

Sharpman

There are piles of old stock rocks from different mines that are being cut in shops and sold.
I believe Hatanaka is the owner of the Nakayama old stock, he rates the stone applies the stamps etc.

As far as stone qualities, you want stone that is very compact . When you talk about speed you need to remember that finisher for razor is a polishing stone, it has to be very very fine, and IME that translates in slow stone, you are no longer trying to remove a lot of metal. TO get best result from your finishing stone you need to use a pepolisher.

Originally Posted by mainaman

There are piles of old stock rocks from different mines that are being cut in shops and sold.
I believe Hatanaka is the owner of the Nakayama old stock, he rates the stone applies the stamps etc.

As far as stone qualities, you want stone that is very compact . When you talk about speed you need to remember that finisher for razor is a polishing stone, it has to be very very fine, and IME that translates in slow stone, you are no longer trying to remove a lot of metal. TO get best result from your finishing stone you need to use a pepolisher.

Stefan, what you say makes sense and I was thinking like that. But sometimes
on gets confused. For example the guangxi stone is hard and removes very little
metal, yet is only 8-12k according to many. I have sharpened knives and plane
blades on this stone and I could hardly see any metal on the stone. Maybe mine
is finer than 12k, don't know.

There are very, very fine stones that are very slow,
but also super fine stones that are much quicker. I would
think the latter is much more expensive. I think 330mate told
me that once.

Sharpman

Sharpman

I think you are spot on with your list of credentials for a razor finishing stone, but I would shift the priorities around a bit to:

1) sheds super fine grit
2) free of impurities
3) works quickly (high abrasive power)
4) rather hard to very hard stone

It really is all about the job appropriate grit, and for razors it has to be the finest because there is no substitute for ultra fine grit as the paste and spray guys factor. Hardness is not at the top of my list but I do recognize the value of a stone that stays flat during sharpening in order to create flat bevels. With razors though it is not so important because the pressure on a kamisori toishi razor hone is minimal as many of us speak in terms of “the weight of the blade” pressure. With those forces stones do not dish very quickly as they will with tools.

Not to belay the subject but finishing planes and paring chisels need the finest edge as you know in order to leave a sheen, jack planes and chisels a steeper and less sharp edge and these choices also reflect edge retention as it relates to work stresses. In my opinion razor hones are too fine for plane blades as you will quickly loose the razor edge you labored for in the first pass on wood. Better to design an edge that has a known sharpness factor with a known retention rate under certain conditions including certain woods.

For razors or any other edge for that matter I like to put the grit quality and fineness at the top of my list because I want to sharpen quickly and move on to the next project. I look at hardness more as a matter of preference and style and not as a factor necessarily relevant to sharpness, the grit should be the most relevant factor in providing the edge, and for a professional, in a dependable and easily repeatable manner. Hardness and fineness are not synonymous. I do not use a tomanagura often, and almost never use white nagura, if I need a slurry I generate one with a diamond nagura (plate) and this gets me kick started with the hard stones but I am depending on the stone to refresh its surface throughout the whole honing session including during the clear water step if one is used. I love hard stones that are full of grit, it is like driving a low slung car with a stiff suspension around a corner. But with a low grit factor it is more like a 1970’s MG rather than an Italian exotic, you are still low and maybe stiff but feel like a tourist.

Why are some stones harder than others, and which ones are the hardest? You are caught up thinking horizontally, you have to factor in the vertical slope of the current strata configuration. There was also a definitive heat event that all these stones went through that is important, a sort of trial by fire so to speak. A long drawn out subject maybe for another time.

Why are some using hard stones? You can PM me if you want to chat a bit. Alx