Natural Stones and other abrasives (are grits just grits?)

[Fred]

If only it had something to do with cutting. I'm still baffled by the interest in "finish." I understand that polishing an edge reduces friction and that's good for most kitchen edges. Beyond that, none of it makes any sense to me.

[ksskss]

Ah but it does. I'll post more about this later when I return from a trip in about 5 hours.

---
Ken

[ksskss]

Well Fred there are both subjective and objective issues. There is also a cultural appreciation here as well. Lets review a few subjective points first and then dismiss that as something of no interest to you and go on to objective issues. It is time to try to loosen your deathgrip on the 'grits is grits' concept and the fallacious 'objective audio analogy' defense of your position on the topic. I hope you view my attempts as a positive learning experience - as it is intended. I mean no disrespect in this topic to you.

So classically natural stones were used long before synthetic stones. It was EXPECTED that a stone should bring out qualities in the metal that accentuated the sword polisher's technique, who was responsible for bringing out the characteristics of the steel as it was processed by a particular swordsmith. Thus one finds a natural stone - or a number of them - to scratch the softer cladding differently than the harder core steel. Natural stones have a much lower hardness ( Mohs hardness, not composition hardness) than synthetic stones and one sees a differential in how that abrasive handles softer steel from harder steel. One also sees this in differentially hardened blades and particularly so along the borderline between these levels of hardness, bringing out structures in the steel that would otherwise go unnoticed with a synthetic finish. A synthetic finish treats the hard and soft steel in pretty much of a similar manner for most stones, with exceptions. The result is a total whiteout, much like turning the contrast ratio knob all the way 'up', reducing the contrast to pretty much of a total whiteout. There is beauty in this. Much of this is cultural too. I find a kasumi finish attractive BUT I also find a perfect mirror attractive too. Does one or the other affect cutting ability - no, not directly so. So I get that this is of no concern or interest to you. It does however exist and is of interest to others.

Now let's get into the grits is grits discussion. Is there a difference between a diamond particle or even different diamond particles and say Aluminum oxide or Silicon Carbide or Chromium oxide or cerium oxide? Clearly there must be some difference here or else MULTIPLE INDUSTRIES from optical manufacturers to multiple industrial processes, stone fabricators, glass fabricators, machinists, etc etc etc etc would all be wrong and you would be right that there is no difference - just particle size. They would all get the same stuff only picking out grit sizes. Clearly this isn't the case. Would it matter if a particle size was tightly specified - exact tolerances - or poorly specified or even inaccurately specified? SURE it would. Would particle hardness or shape matter? If a particle looked more like a beach ball or a sharp edged multifaceted structure, would that make a difference? Would a carbide fare the same with a particle harder or softer than it? Of course. If the particle was more flake shaped with dimensions of length width and thickness completely different, could you even specify an accurate grit to this, even moreso if it changed these dimensions with use and the surface characteristics had more to do with it's abrasive qualities than it's actual dimensions? Would abrasive density be relevant - would a stone with few abrasive particles act the same as one with a heavy density of particles? I hope this is obvious. To reduce the discussion to a univariate description of a particle and ignore all of it's other characteristics is not an objective or scientific description of the parameters that affect the results. If I've misstated your position that grits is grits and that just the grit size is the single criteria for understanding an abrasive's performance, please correct me.

So now we go on to natural stones. Here we have a relatively more heterogeneous distribution of particle sizes, particle hardnesses and particle shapes. Indeed, accurately characterizing this with a grit number is pretty meaningless. Can we be objective about this? Yes. The finish is more of a matte finish under the scope, somewhat like a sandblasted finish. A synthetic finish is typically defined by a scratch pattern more like rows of corn. This is an objective visible difference - they don't even look similar. Depending on the steel's hardness the scratch pattern is different too. Would you assign a grit value to rows of scratches that are perfectly uniform - yes and you would be somewhat accurate depending on the types of scratches the particles leave. This is all objective reproducible data. This is not the type of data one gets asking about sound differences in various copper wires - an apples and oranges comparison at best - or if one sound 'feels' better than another. This qualitative sound data with all of it's lack of objectiviity and irreproducible results is not at all the same as the quantitative date in this discussion. Would the laws of parsimony dictate that we assume a difference in two totally different patterns from natural and synthetic stones or would we assume them to be the same? You know the answer.

Now if the scratches in the edge are of a certain dimension, this strongly implies the 'edge of the edge' has a certain type of edge - roughly the extension of the scratches as they meet the edge of the edge, with finer scratches producing a finer edge - ignoring burrs and fractures produced by the edge from breaking off burrs for the moment. Now if the scratch pattern is non uniform it stands to reason that the edge will also not be a homogeneous distribution of scratches either. Thus as one level of scratches (teeth) wear off the less prominent scratches come into play. This results in a different process of edge degradation and failure - a more prolonged level of function than a more uniform distribution which would have a single point or level of failure. It also implies a more complex 'toothiness' with both refined and less refined edge characteristics resulting. this results in a different interplay between slicing and push cutting performance. Try cutting a paper towel with two edges and you will see a quantifiable difference.

Another area of discussion is the binding of the abrasive. This has implications on the rate of abrasive release and the hardness of a stone. Both of these characteristics have implications in the ability to effectively apply an abrasive to a task, with harder stones giving more precise edges and softer ones giving a less precise but more accommodating edge, each with it's advantages and different results regarding the flatness or convexity of an edge used under the same circumstances. With synthetic stones this is controlled by the binding agents, not the abrasive, with binding agents ranging from magnesia, resinoid, sintered, and even in industrial processes in metal bonded preparations. This has a marked effect on performance, longevity etc etc. With natural stones there is really no unique differentiation between binder and abrasive. They are largely one and the same with components contributing to both parts of the equation from the skeletons of the radiolaria and the oceanic 'ooze' and volcanic particulates that make these unique formations to the geological as opposed to industrial means to which these stones are produced.

I hope this begins to be a good starting point to going beyond the grits is grits stance into a more multivariate viewpoint about the qualities of abrasives and how they affect the sharpening process.

Fred, could you tell me what natural stones you've tried - both Japanese and otherwise? And on what sort of steels. I'm trying to understand the objective data that you base your supposition that this has nothing to do with cutting ability. Again if I've misstated your positions on this topic, please correct me.

---
Ken

[thombrogan]

the fallacious 'objective audio analogy' defense of your position on the topic.

What is fallacious about Fred's analogy comparing "audio junkies" to "stone junkies?"

[ksskss]

Well I'm in complete agreement with Fred's views and ideas regarding audio and subjective qualitative measurements - and the observer bias and lack of reproducible results and placebo type effects etc, but the comparable situation isn't applicable to this discussion regarding stones as there is objective data to support it. IMO. I'm not ascribing any evil notions here, just an alternative point of view and answering an asked question. Thom, as a person who has expressed opinions of one stone over another, what are your thoughts on the matter?

---
Ken

[thombrogan]

Aside from cosmetic preferences and preferences on how to achieve them, I go more into "grits is grits" territory every time I resharpen my favorite snippers.

Now for objective data, if you mean on finishes, I'll accept it with minimal criticism (studied and applied lapping theory as part of my enjoyment don't you know). If you mean on edge performance, where is this data?

[ksskss]

Thom, since this is of genreal interest to sharpeners and not really a trading issue, perhaps this thread should be moved to the sharpening section so we can explore this data in more detail.

---
Ken

[wsf]

Here's a portion of a long treatise on sharpening by Alex Gilmore of thejapanblade.com. It's a great explanation of how natural stones do what they do. Not putting it here to argue for or against anything; it's just a nice piece of writing and, as a bonus, contains the word "radiolarians."
-----------------
Natural sharpening stones, the type found near Kyoto but also in other parts of Japan, are complex in their material make up and contain tens if not
hundreds of different elements and compounds. Some of the minerals and fossilized organic material act as cutting and polishing agents while
some make up the binder portion of the stone that holds everything together. The harder minerals like chert, a form of flint, do most of the cutting
while clays mostly make up the binder. Users of Japanese stones notice the contrast between the hard steel and the soft iron after sharpening; in
Japan this is called Kasumi. Kasumi is a word that describes the fuzzy or hazy look objects take on when viewed over hot summer ground. The
kasumi look is desirable to most Japanese tool users but few understand how this effect is achieved.

Taking into account the hardness of these blades, in the Rockwell 60-65 range, only a fraction of the available abrasive grit mix in these stones will
actually polish the hard steel cutting edge; the clay certainly will not. But conversely because the iron backing on laminated blades is so soft almost
every thing in the grit mixture will affect the polish of this softer iron material, even the softer flakier grit particles.

During the sharpening process the soft iron has been honed and reduced in mass by the effects of all of the grinding compounds working in
unison. The chert which cuts the soft iron like butter and the clays, salts, radiolarians and even some silica that is a known element of some of the
older wrought irons will help to sharpen or reduce the jigane soft iron as it is coaxed out of the iron base. The kasumi effect is basically the result of
all of these lesser abrasives working together to sort of massage the surface of the iron, none of the abrasives acting on their own to overpower
the other, a little bit like Judo, which translates as "the soft way". The iron is changed and reduced and sharpened, but in a soft way.

The hard tool steel takes on a polished mirror look; some suggest it has the look of chrome. This microscopic scratch pattern in the hard steel that
makes it look polished has been cut by only the hardest of the hard abrasive particles and it looks regular and finished. The soft iron on the other
hand looks dull and complicated. This is the contrast in the polish that is achieved with the natural stones. Synthetic stones give an over all highly
polished bevel while the natural stones allow the soft iron to look soft.

[ksskss]

radiolarians are beautiful creatures in their own right, with such variety as to compare in diversity to the patterns among snowflakes. Some of my best friends are radiolarians The quoted text says it very well with little to disagree with - nothing at all really. It does address the aesthetic considerations nicely.

Thom, do you feel that the knife industry is unique in this regard that grit number is the single variable to determine sharpening performance (a point I disagree with) or do you feel that this is universal to all industries that use abrasives? I just want to see how deep the rabbit hole goes here. Also does this grits is grits concept extend past stones to sharpening belts, sandpaper, etc?

---
Ken

[Fred]

Ken. I'm not suggesting that different stones don't scratch the steel differently. I'm not suggesting that they don't impart a different finish to the edge. And I'm not suggesting that the subject isn't interesting and filled with cultural elements. What I'm suggesting is that these things don't affect blade performance in any meaningful way. I've only owned and used two natural japanese stones - both finishing stones. I have no idea what to call them. They did a perfectly competent job of doing what they were supposed to do. I liked the way they developed their mud quickly. The blades performed nicely after their use. I would say the finish on the edges was cloudy or "kasumi" compared to the brightly polished edges of the synthetic stones. Whether this was a function of the grit size or average grit size or whether it was due to the shape of the abrasives, I don't know. I only know that the edges performed about like I would expect after work with a finishing stone.

I have actually done some bias controlled testing on knife blade performance but never any tests that tested natural finishing stone edges against syththetic. Common sense would tell me that the polished edge should develop less friction than the kasumi edge. Common sense would also tell me that the difference is so slight that I wouldn't feel any difference in the actual use of the knife. And I don't feel any differences in terms of cutting power. These are subjectives things as are your reaction to the natural stones.

If you refer to the toothiness of an edge, then I suggest that is a result of grit size just as much as it is a result of abrasive shape. People, you included, misunderstand what I mean by grits is grits. I don't mean the results of different stones of the same grit size are exactly the same. What I mean is that they produce exactly the same blade performance. Nothing I've ever read has deterred me from that.

Finally, the case of bias controlled testing. Human bias is very strong. I studied it enthusiastically for a long time. If someone like you who is biased toward natural stones were to make a cutting comparison subjectively, I'll bet a dime to a dollar you would favor the natural stone edges in your results. It is human nature. The question is would the results be the same if you didn't know which knife was which. I'll bet a dime to a dollar the results would be random. Our beliefs and biases are stronger than our sensual perception when the sensual perception deals with subtle changes. I've never seen a bias controlled test conducted in this matter, probably because it too obscure a subject. So my opinion is no better than yours. My purpose in buying the natural stones was to see if they provided anything I couldn't achieve with synthetic stones. I decided there wan't anything for me. I'm not against natural stones at all. My problem is the notion that they impart some extra performance to a knife blade. I've not experienced any extra performance myself and I've seen no scientifically valid tests on the subject that indicate such a thing.

Incidentally, I don't think anyone can tell the difference between two knives sharpened identically, one with a 6000 grit synthetic finishing stone and the other with an 8000 grit or 10,000 grit or whatever. These things get into biases, belief systems, preferences, history, opinion and hobbyism if such a word exists. In the practical world they don't matter a whit any more than two audio amplifiers with inaudible distortion and a flat frequency response would sound different. There you go. There's your audio analogy.