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

Originally Posted by alx

Stefan
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.

I think they are looking at J-nats the wrong way , people always try to quantify things , using grit ratings is one of the ways to put "measure" to a stone. People will say "I want finer stone" while they should be saying "I want harder stone". I think it is not hard to imagine that a stone that releases abrasives esier than another stone will not provide the level of refinement of the latter.

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 collect because I like to try variety from as many mines as possible, kiitas, asagis, suitas etc. as many as I can. They are all different in characteristics such as speed and feel but the common denominator has always been hardness, it directly correlates to the level of finish IME.
About hard vs soft stone, this might be a question of opinion, what I consider soft could be someone's hard as far as Jnats are concerned.

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?

I would think if the study was done at a major university, then it was systematic enough to produce results that are not controversial and provide enough proof for them to make the statement.

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.

This could be the result of the slurrying method, using diamond plates to slurry may cause bigger size grit to release from the stone. IMO a proper way to create slurry would be to cut the stone and use one piece as tomonagura , then one would have the pourest and true slurry for the experiment. I would think that is what those guys did in their study, I do not see any other logical way of doing this.

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.

IMO that is why different stones act differently , but what makes them similar is the way the stone was formed in terms of geological process, the structure of the stones is the same and this would explain the why the grit releases the way it does.

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?

From what I have been told, hype plays huge role in market demand, for example Nakayama is very hyped for being the best. I am sure there are great Nakayama stones out there, but so there are great stones from other mines too. Stones that are lighter in color such as Kiita and usually most suitas are very much sought after (I believe Okudos are very light colored cream to pure white not many asagis?) The reason being that people like to see how the steel is abraded on the stone, which is not as easy on dark asagi stones. Wood workers, which are a lot in Japan, demand such stones. Apart from the hype, add the fact that those stones are of high quality , uniform, hard enough for tools, fast abrasion, good finish, less and less stock left available and the price goes up.

This is an interesting topic, please keep it going.

I do believe that the particles of jnats(natural stones in general)
get smaller because when I use a slurry on a hard stone and
sharpen my plane blades with this slurry there is at first a strong
sound, that after about a 30 seconds or so is much quieter.

That said, I have yet to see a real proof that Jnats can give
30k or higher finish. I like Alex ''Grit testing'' pictures, but it
does not really convince me. It would be interesting to see
the edges of a very fine jnat compared to a shapton pro 30k
at high magnification. I think this can be best accomplished
by sharpening a plane blade with a microbevel using a honing guide.

So put the blade in the honing guide and set the angle higher than usual
to create a small microbevel.
-For the synthetic,start at 1k, 2k, 4k, 8k, 16k,
30k. Something like that to get the best result possible.

-For the jnat it becomes more difficult, but a fine aoto perhaps to start with,
then go to a harder stone to get a prepolish result and then a very fine
jnat with slurry perhaps finishing on water only. Or use the synthetics up
to 8k and then continue on very fine jnat to see what changes. No expert
here just giving an idea.

I think comparing the edges at high magnification(500-1000 prefferably higher) would
give us the best results. Magnification at 25 times isn't really that impressive.

So anybody got a high magnification miscroscope?

Sharpman

Use search funktion in forum or google, there are plenty of comparison images out there, even Alex have them.

I don't think that the "slurry pictures under a microscope" shows us the grit of a stone. They are pieces of abrasive glued or whatever it is called with pieces of the binding material. I don't think those pieces are actually the grit of the stone. Maybe if you take an X ray after, with this slurry, again under a microscope, we can have a better understanding (if the abrasive and the binder have different density). A good way to find out which stone is finer, by my opinion, would be to polish or burnish its surface to the highest degree(not with diamond since it will abrade out abrasive particles), and then take a look of how fine its surface looks under high magnification. You will not be able to see the whole size of the particles, but the size and shape of edges on the surface, compared to others, might be helpful.

Originally Posted by maxim207

Use search funktion in forum or google, there are plenty of comparison images out there, even Alex have them.

Like I wrote in my previous message, magnification at 25 times does not
convince me. Alex's pictures were magnified at 25 times. I think Les also
posted one picture, but it was at 60 times magnification. I would like to
see higher magnification, like 400 or more. I wish I had a microscope, they
are much cheaper nowadays, so maybe buying one would be a good idea.

Sharpman

Originally Posted by SharpMan

Like I wrote in my previous message, magnification at 25 times does not
convince me. Alex's pictures were magnified at 25 times. I think Les also
posted one picture, but it was at 60 times magnification. I would like to
see higher magnification, like 400 or more. I wish I had a microscope, they
are much cheaper nowadays, so maybe buying one would be a good idea.

Sharpman

Alex posted a link to my thread in which you can see SEM images.

A microscope, even one with 5000x magnification will not be enough. Those particles are not pure abrasives. They are both pure abrasive particles, pieces of abrasive with binder, and binder particles. If the binding material is made from Mx(CO3)y, M=metal, we can use an acid to dissolve it, as long as the salt is easily dissolved. If the hone is pure enough, we can see then under a microscope the size of its abrasives. I don't think this will work for the Japanese hones, but if we can find their exact composition for the binder and abrasive, there are ways to do the same thing. The binders of the hones are not getting powdered instantly when we lap the stone, they remain as pieces, they are just too soft to abrade steel.

Originally Posted by mainaman

Alex posted a link to my thread in which you can see SEM images.

Stefan, I remember that thread. It shows the particles themselves. I am
interested in the edge at high magnification. If the edge proves to be as
good as a shapton 30k or better, well that is prove itself that the particles
become smaller and smaller.

Sharpman

Originally Posted by SharpMan

Stefan, I remember that thread. It shows the particles themselves. I am
interested in the edge at high magnification. If the edge proves to be as
good as a shapton 30k or better, well that is prove itself that the particles
become smaller and smaller.

Sharpman

The abrasive from the shapton 30k are not equivalent to 30k grit. You can clearly see it from its scratch pattern. The scratch pattern from a coticule is much finer. (we are not talking about shaving performance, just the grit) CrOx 0.5 micron is around 30k grit. Who would dare comparing the shapton 30k with the classic CrOx? The size of their particles are supposed to be 0.49 micron, but the company said that the scratches it leaves are near 0.49 micron. That is a huge difference.

Originally Posted by Vasilis

The abrasive from the shapton 30k are not equivalent to 30k grit. You can clearly see it from its scratch pattern. The scratch pattern from a coticule is much finer. (we are not talking about shaving performance, just the grit) CrOx 0.5 micron is around 30k grit. Who would dare comparing the shapton 30k with the classic CrOx? The size of their particles are supposed to be 0.49 micron, but the company said that the scratches it leaves are near 0.49 micron. That is a huge difference.

Ok things just got more difficult. Which pictures are you referring to
when you said the scratch pattern from a coticule is much finer than
that of a shapton 30K?

I was under the impression that CrOx 0.5 micron was the same size
as the 30k Shapton particles.Vasilis where do you read that the scratches
left are 0.49 micron?

Sharpman