Thread: Natural Stone Grit Confusion

This question is mostly for the people who actualy are able to estimate the grit of their naturals and in particular apanese stones. From my very limited experience in with my Nakayama, I would have a difficult time giving an estimate of it's grit and I know some people are able to estimate. When you estimate, are you giving an average of how it is cutting freshly lapped?
I start out with a slurry cut in with a DMT. At that point, the grit has to be pretty low, as it is cutting very fast, but not so low as to leave deep scratches. Maybe a fast cutting 5000? Then moving to water I hone and eventually gradually lightening pressure and finish up to where I can shave. Since it produces a uniform haze finish, I would not even begin to know how to estimate the final grit especially being "raised" on synthetic hones where you can literally see bigger scratches for 1200 than 8000 etc.

Could it be as Alan Watts said of Zen ? Those who know don't say and those who say don't know. I haven't got a clue.

In doing a comparison, there are a few things to consider, but the level of polish and/or scratch pattern are, imo, not the best to go by. I mostly go by the way the edge feels off a hone, and say something like "hone x gives an edge like hone y."

the place I got my Japanese finisher, has grit test pics.
Alex has probably dealt with Japanese stones since forever so I trust his grit estimates.
You can ask him if he is willing to test your stone and give you a grit estimate.

I was just going to mention Alex Gilmore's photo tests. One thing about those tests, though. They certainly contain more objective information than any other method in that they are based on photographs. But it seems to me like the estimate of a grit based upon the appearance of striations in metal in a photograph is pretty imprecise too. I'm not doubting Alex's estimates, as he seems to know what he is doing, but I wonder whether anyone else would be able to take the same photographs and reach the same conclusions without the kind of background and "feel" for this that Alex does.

Originally Posted by JeffE

I was just going to mention Alex Gilmore's photo tests. One thing about those tests, though. They certainly contain more objective information than any other method in that they are based on photographs. But it seems to me like the estimate of a grit based upon the appearance of striations in metal in a photograph is pretty imprecise too. I'm not doubting Alex's estimates, as he seems to know what he is doing, but I wonder whether anyone else would be able to take the same photographs and reach the same conclusions without the kind of background and "feel" for this that Alex does.

Only photo evidence is not good enough, Alex has a lot of experience and that is what gives credibility imo. a better test would be to work the slurry on a natural stone then take an SEM image and see whats the size of the grain.

Let me say first that I tend to be pompous and long winded, so beware. Those of you who have read some of my other articles know this, and I apologize if I tend to repeat myself. Although I shave with a straight my years spent on stones has been mainly in regards to carpenters blades.

Japanese stones have been used for so long without any numerical number system attached to them partly because they come from a country that lived and existed in a way that, at least in the past, tended to favor words over numbers while describing objects that occurred in nature.

The words arato or shiange tended to be sufficient enough to describe stones that in the in the hands of simple workmen would perform a simple task.
　
In Japan it is usually understood that you should test a stones ability before you buy it, and that is still a good idea. But because I brought these stones to the U.S., and set up a website, I felt the need to provide some numerical system to use as a tool for description so that maybe a long distance conversation could begin based on common ground. I chose the Shapton 30k on glass stone as the finest “commonly held grit” in the market place as a marker of sorts. I bought my 30k stone from Harrelson Stanley, and borrowed a few other Shaptons from a friend and began photographing the scratch pattern left on Japanese laminated blades as a build up or a library of scratches for comparisons alongside the natural tennen toishi scratch patterns.

In all honesty, I was very nervous at first about publishing these early photos of the grit patterns from Shapton stones because the scratches did not change very much and there was a lack of delineation between the 15k to the 30k stones. I spent hours and hours and many cut fingers trying to get photos that would define a sharper more defined step between these two stones. One time I made 500 laps on the 30k stone to try to get a finer polish and in the end all I got was a burnished blade surface, it did not sharpen the blade any further.

The proceedure for the photos of all the scratches left by both natural and synthetic stones were, with a freshly lapped stone but with no slurry and were the result of between 25 to 50 forward edge into the stone passes at right angles to the cutting edge. No drawing the blade back in contact with the stone. I first lapped the stones with a diamond Atoma plate to open up virgin grit, washed the surface with fresh water and then sharpened on that surface with no slurry. To get beyond previous scratches from previous stones I side sharpened the blades edges first so that optically there would be no 90 degree to the blades edge scratches visible. All the photos were taken with the light coming from a single source to the left and at 90 degrees to the scratches. This is a raking light meant to highlight the peaks and valleys of the scratch pattern. In this way any scratches running parallel or greater then 45 degrees in line with the light source are not visible because the light fills up the valleys.

There will always be scratches in steel left behind from an abrasive action. If you see lower magnification photos, like I take, of a surface without scratches it is because it’s either a highly burnished surface or because the scratch valleys are filled with light when the photo was taken. After all sharpening is just the removal of steel, and a shaper blade is just that same task done with finer grit abrasives than those used before. The caveat being low magnifications, of course with higher magnifications scratches will eventually appear in the photos although possibly ill defined.

I had waited a couple of years, watching all of the forums hoping that someone else, more scientific then myself would stick their neck out and say, my tennen toishi is 15,000 grit, and this is why. Or this one is 24,000 because I measured it and this is how it was measured. No one would venture beyond “it is hard”, “it is fine”, “it is the finest I have ever tried”. So-san even when so far to skirt the question completely by only by passing on that “my father never talks in those terms” and suggesting that no one else is Japan does either.
　
　
Think of it, why would Shapton or Norton take the time and cost to measure the grit particles of a natural stone? They do it with their own stones, they grade them by microns and ascribe numbers. It appears that the mystery surrounding the grading of natural stones seemed better left not said by those with the resources to demonstrate such facts. The miners who by risking dangerous conditions extract these muddy gems are too busy to bother and in any case the domestic market is not demanding it of them.

The system I used to photograph the scratch pattern for my website can be copied for about $50, and you end up with a great camera to use for other things. This system using a Bushnell Portascope and a Olympus camera was designed so that others worldwide could copy it by buying the items on E-bay, and I hoped it would create some common ground for a conversation to begin. Now granted there are better ways to take photos, sharper lenses, higher magnification, more consistent comparison grit particle medium, etc. but my system has only 3 components, the light, Portascope and the camera. But believe me I have been waiting for someone with access to a university lab to really get into it.

I have also found however that you can magnify a scratch pattern too closely, sort of loosing the trees for the forest syndrome.

There is another quality that is important to the sharpener that is a little more difficult to quantify, and that is the use ability of the stone, how well does the stone perform. We describe this when using synthetic stones; the stone cuts fast, or it loads too fast with swarf, it is soft and dishes quickly, etc. We ask, how good is a stone that glazes every few strokes? There are a lot of factors in how we choose stones. In synthetics we tend towards brands that feel good with some steels, shun others that don’t or even go to the expense to match up stones for particular steels we keep in our quivers.

In many ways the language we have and use is too crude for the job of describing the complicated yet subtle task of sharpening with natural stones. Ascribing numbers will not do this completely, they may help some but really in the end it does come back to testing out the stones first. Like they say, the proof is in the pudding. Alx