Thread: What is Grit in Japanese Natural Stones, and How Important Is It.

What is grit and how important is it in the natural japanese awasedo.

Why are we so enthralled with the japanese awasado for razors, aren't there various other natural stones from around the world that are just as useful? So with that said, for now, and just for sake of discussion, lets just take the unique beauty comments off the table here, and get down to the nitty gritty. What is grit and how important is it in the sharpening process. Alx

There are terms here that can be defined as:
Grit=abrasive
Sharpening=honing
Bevel=the flat portion
Edge=the convergence of two planes (point=three planes converging)
Hardness=as in how tight the grit is held by the stones binder material
Polishing=refining or flattening of a surface

Although there may be other options here, and hopefully forthcoming, there are in my minds eye 3 ways to relegate and utilize the surface of an awasedo, all of which are in use and popular right now and discussed on this forum;
1) As a sharpening platform from which to add different foreign material like hon-nagura, Aichi-nagura, diamond dust, etc. to aid in the sharpening of a cutting edge.
2) To perform the physical actions of honing an edge with the intended act of not releasing any slurry from the surface of the awasedo.
3) To with purpose, release with the use of a diamond plate (DN=diamond nagura ie. DMT, Atoma, etc.) the top layer of the bound up grit with the specific purpose of utilizing that loose grit knowing that it represents the true unadulterated nature of said host/base awasedo.


To lay my cards on the table, I look at the grit of a honing stone as a layer of abrasive material, and I think of it like this.

The grit of an awasedo is like surface of a plain piece of standard thickness copy paper like we use in our printers. The grit is surrounded by clay like binders that hold the stone together and determine its relative hardness. To the average person it just looks like a stone, to a honemeister it looks like a sharpening stone with possibilities. The physical size of one layer of the grit particles determine the thickness of the paper in my scenario, small particles=thin paper, large particles=thicker paper. This top surface of the paper is a two dimensional model, and it can be said, and argue that the above #1 & #2 systems popular in use relays upon the two dimensional model.

My minds eye approach to the #3 system however looks at that piece of paper as a three dimensional object, one with a front, back & sides. Because I acknowledge the three dimensional quality if the grit is mechanically released from the host stone intentionally at the beginning of the honing session, the bound the grit can easily act upon the bevel and the edge in a much more aggressive manner and in one that mimics the three dimensional character of the grit. Almost everyone agrees that the grit particles that make up the awasedo will break down through use, I call it cleave. If the grit cleaves once during the honing process, what it to prevent it from cleaving again. If it does cleave then the 2 micron particle become 1um, cleaves again a .50 particle. If that is so then the grit is immediately in the 20k-30k range. This is the reason that edges off an awasedo will shave on par with a super fine grit synthetic.

If my memory serves me correct, Stefan aka. Maniaman had some SEM photos taken of the slurry from an awasedo which were posted on the SRP forum about 2 years ago. These photos pictured the various sizes of the awasedo grit particles and many of them were in the 1um range and none were larger than 3um if I remember right. The particles looked thin and fragile, not round or football shaped.

http://straightrazorpalace.com/hones...rry-study.html

And although the sample may have been contaminated by the Escher, the photos show the fractured possibilities provided by natural stones.
The well know sharpening expert Leonard Lee in his book, The Complete Guide to Sharpening has some similar photos as does Toshio Odate the master Japanese woodworker which I believe are relevant. Alx

I have no idea why other people might like their Jnat, but I like mine because of the grit - no other reason, although it is a nice blue colour.

I like your thoughts on grit. I think of grit more as a measure, and tend to think of what you are describing more as the media itself but I don't think that is either here or there to be honest. I only have a marginal understanding of the physical nature of Jnat abrasive particles - I've seen some of the photos you mention, I've talked to some of the experts, and in the end the idea is the same - abrasive particles suspended in some sort of binding media. The only thing that seems to come out of Jnats is that the abrasive particles break down somewhat - I'll believe that though it is only via honing that I have any evidence (if you want to call it that) of that behaviour.

My main interest is the measure itself. It is pretty well acknowledged that you cannot get too specific with the grit measure on any natural, let alone Japanese ones. I think given the physical nature of garnets you could probably be more specific with Cotis and BBWs, and indeed I think you do see this somewhat, particularly nowadays what with the excellent and detailed work being produced by the Belgian Ardennes Research Team

In any event, I'd like to argue from a measure point of view that the current method of grit ranges for Jnats is entirely appropriate. Take for example the idea postulated above - a grit (or several) splits to 0.5 micron or perhaps smaller - there's no reason, or none I have ever seen talked about, to assume a grit will cleave precisely in half, although from a statistical perspective it is probably the safest assumption to make in the absence of any experimentation or detailed study of grit breakdown behaviour in Jnats. At any particular moment in time during honing there will be a mixture of particle sizes floating around under the razor - a mixture of new particles just-released from the binding media, plus a certain amount of broken down particles: to take the example from above, there would be some 1 micron bits bumping around with some <1 micron bits.

So there's going to be a hodge-podge of scratch sizes left on the edge, and I seem to recall this is something So Yamashita talked to me about way back when. I think his argument was that this grit-size "diversity" is what gives a Jnat finished edge its more "robust" feel - but I may be wrong about that. Half of what So says goes right over my head.

To make a long story short (too late!! ), how do you assign a grit measure to a stone that does that kind of thing? I suppose the safest way would be to associate the measure to the maximum grit size of particles, and/or perhaps allow this measure to vary with time (if you could isolate or stop the new-release particles, you might be able to make mathematical assumptions about how this grit decreases geometrically, maybe....). Other things you could do would be to make assumptions regarding the rate at which new particles are released, how they are distributed, the rate at which they break down and split etc - a stochastic birth/death process perhaps.

James.

From what I have read here, the grit of the finest Japanese naturals is around 2 to 1 micron. Then they brake down into smaller particles, which means, the particles with the 2 to 1 micron sizes are not the actual abrasive particles. Personally, I prefer the UK hones over the Japanese. Grit is important, but not the most important aspect. As I said before, the grit of a coticule is 5 to 15 micron, but they work like a 1-1.5 micron hone. The shape of the abrasive, is also important. And its composition. And the hone should not be very soft. There are too many variables, and we simplify them as "grit". Is kind of makes sense, but a fine grit stone doesn't means it will be a good hone.

Yes, you are quite right - there are many variables that go together to make a natural hone but I would not say there were too many - just that we have not looked into them all in any detail, we seem to side-track onto grit size a lot. I guess it is like horse power in a car - other things are important, but the old hp is the glory spec.

However, I think we are invoking the ceteris paribus principle - other things being equal, what is grit? That is my interpretation, anyway.

James.

This can be a complicated subject if you want to really understand it.

You can go to your local library and get a Petrology textbook and learn the nitty gritty about rocks and the types and how they form and all that. That will give you an intro into understanding how and why rocks behave the way they do.

Just from what I have learned though my quest to find my own natural whetstone materials. The most important thing I learned was that most whetstones you read about will say that they are just sedimentary or metamorphic, but that doesn't account for subgroups. Actually most good whetstone material is in a subgroup called metasedimentary, which is sedimentary stone that has gone through a very light metamorphosis be it pressure or heat slightly changing the microcrystalline structure. It really helped me narrow down to rule out a lot of stone and what to look for in my search. Just knowing any good whetstone will be sedimentary or metasedimentary, which still has sedimentary origins.

I admire those who are of a scientific mind. Where would the world be without them ? I am not gifted with that mindset. I grab a rock and lap it, hone, and if it works I'm happy. If it doesn't, I grab a different rock. I've been on this forum a number of years and had a pile of rocks, I still don't have a concept of what 'microns' are relative to hones. I remember when I first came around hearing that chrom-ox is 5 microns ? Anyway, I like chrom-ox however many microns it is, and I've learned to hone a razor in the last few years. Enjoy reading y'all's conclusions too. I might even learn something after all this time.

Maxim

I have found it true that not all wholesalers know about all stones. After all, wholesalers are just consolidators, they collect stones from one source and sell it to another source and many companies are run by accountants. Some wholesalers have, but not all of them have actually worked in a mine, and because of this lack of underground work so much of their information is not first hand. For that matter not all mine owners are or ever were actual mine workers, I know of three cases where the mine owner simple inherited the mineral rights and had other careers during their young adult lives, Hatanaka-san being one (I don't think his father was a miner either), Ishihara-san is another and the third is Hitome-san. Nakaoaka-san would make four. I might think of others later. Working in the mine and drawing out each stone layer by layer pound by pound is the classic geology lesson, leaning it in school can work but, only hardly. Sitting in a sales office in Kyoto, I don't think so.

Also I have found that some mine owners know or at least think and act like they know a lot about their own mine, but in reality know very little about someone elses mine. Easy for me to say, sure I never risked my neck in a mine tunnel. But through observation and cross checking some truths are apparent and I have bought more than once some very valuable stones from one miner who sold it to me as from "his mine", when it was not from his mine at all. Also I have found that mine owners in general know practically nothing about kamisori or about fine tools or how to sharpen them. They can judge stones as to their wholesale value, but they know only the tools of their trades. This is a generalization I know, and I will be criticized for it, but this is what I have found true.

Now guessing about a stones provenance by a photo, I agree it is risky. I would not myself use the term "ridicules"(sic), but it is risky in an armchair sort of way. I can definately tell a Hon Suita from a photo in most cases because I have owned at one time or another over 40 pieces, Shiro suita I can nail down from the same perspective, these are sort of easy. An asagi from a tomae strata is not too difficult, or Karasu from the Aiisa. The Aka-pin stones can jump out in a photo, Ki-ita are not too difficult especially if they are wet. Renge is only found in Suita stone as is Momiji, Gousa a deep strata tomae found next to Aiisa strata. Uchigumori in the hand is easier than by photo but looking at the edges can be telling. Come to my shop someday and we can go over others.


I enjoy very much Jim Rion's blog, he seems like a very truthful person. I did notice the blog entry you cited where he went on to say that hardness trumps fineness. Jim went on to say way before his first mention of hardness,

"Oh baby. It's gorgeous. Silky smooth and fast, fast fast."

The smooth factor feeling is a hard habit to kick. I know that particular "silky smooth" feel of a Nakayama, and I can attest that feeling is much different from an Ohira or Takashima.

It is a risky statement, in my opinion to claim,
" the main abrasive in Kyoto finishing hones are particles of Silica, ranging from 2-3 microns in size. 2-3. That's the size of the particles in a 4K to 6K artificial stone. ALL of the stones they measured fell between those marks, from a variety of mountains and strata".

I have some trouble with that broad statement, would never say that myself because I can feel the difference between a coarse stone and a smooth stone with my hand. In my book, smooth=fine. But at the same time I do not fault Jim for quoting a study if he feels it is pertinent information to pass on.

I love awsase-do, they have been a part of my life for 35 years now. I admire the longivity of this thread too, the J-Nat club is wonderful name and this thread continues to be a wonderful stream of enjoyment. Alx in Sonoma

Originally Posted by maxim207

To name a strata with a stone is just pointless to me there are so many stones and so many layers that it will just confuse buyer in the end.
If you go to any wholesalers in Kyoto they will tell you harder stones is from Aisa medium is from Tomae and softer from Tenjyou, but I will bet that they dont even know them self what stone come from witch strata and even from what mine, they also say it that they are not sure and it is not important. Miners might know it but there are very few of them left. I know only one man in Japan that can do it by trying a stone that many wholesalers go to if they dont know what they have !
To guess stratas from a picture is just ridicules.
So for me it is a huge guess competition and pointless discussion what stone is from what strata. Will only confuse you even more in the end !

Stefan

Has it really come down to us believing that all of the stones, no matter from which mine or from which strata all contain the same grit particle size of 2-3 microns. I do not believe that. But there again I am trusting in my own judgment.
If the case is true that all the stones are in the 2-3 micron particle size level, then why is everyone looking for a finer and finer finishing stone. Why did you but 60 stones? Or are you trying to say that what everyone is looking for whether they know it or not is a harder and harder stone. Which is it? Buyers are asking me for a finer stone, should I steer them to a harder stone?

I do believe some of what I read, but not everything. I do not hold Jim beyond his reportage, he has done a good job by opening this conversation.
I myself do not finish my razors on rough stones just because they are hard stones. I know that not all stones are created equal. And I hone my perfectly sharp and comfortable edges with a slurry. This whole stone conversation is way bigger than any one of us, it has been going on a long time and in the case of the Japanese stones, in a different language. There are subtleties in the Coticlue mines, there are great variations in the Kyoto mines too.
As in any testing, by Tokyo University or whoever, the variables are in the sampling. What stones were used. Did they visit mine sites or stores for samples? How were the samples taken from the stones? All these mines were closed at that point, 1982. Did they sample stones from Tamba or just from Yamasiro? Free samples or did they buy them on the open market?

A blanket statement of 2-3 microns seems very narrow to me. I would have thought of a much wider range. But I am opinonated. Looking at your SEM photos and those of Leonard Lee and the Odate-san photos I see huge variations.
It has always been my understanding that the mineral particles that make up the awasedo of Kyoto was a aeolian event
Aeolian processes - Wikipedia, the free encyclopedia
where the winds sorted out through gravity the heavier and coarser particles from the finer lighter particles. The stones in one area contain certain particles and other areas contained different one.

If this is not true than what is the big deal about Ozaki or Okudo or Nakayama? Why is a stone from Okudo worth so much more than a stone from Okatana or Okabana near Kameoka? Why have historically stones from certain mines been in demand or maybe even ordained by the Imperial guard as noteworthy?

In short, what is the research, gotta be more than one quote? Jim! Which page? until then, with regards, Alx