What is hardness in a finishing stone, and how does it affect its finishing character

[alx gilmore]

I saw this question earlier today, and it seems to me to be worth some discussion. I quote Filarmonicafreak,

"to the jnats, i am thinking that the harder stone is finer. is that right?".

I see this question as two seperate issues, the hardness issue & the finess issue. Any ideas?

 

[Obiwan]

Not sure what he meant exactly by "finer". Finer grit or finer as in a sign of quality? (Maybe he can ellaborate). As for me, I find that a quality edge can be achieved with either type stone. It's ones technique that has to be altered slightly to yield the desired results. I have some ultra hard stones and some softer ones. I've learned over time (thanks to you. lol) great results can be obtained with most of the JNATS out there. It's just a matter of adapting to the stone.

My preference: I prefer as stone a spot or two below the ultra ultra hard ones.

 

[Gamma]

Hard is hard, fine is fine.
Hard does not equal fine, fine does not indicate hard.
They are two different concerns if the word fine is meant to indicate the size of the abrasive particles in the stone.
6k is finer than 4k, and so on.

Some confusion occurs, often I think, when people say things like "this stone is ultra hard, for experts only" - that seems to translate into "experts want the finest stones so the hardest stones must be the finest."


The Kyoto Whetstone Org has published a report claiming that allJnats have particles in the 2-3 um range, which is about 4-6k.
If that's an accurate statement, the concept of which stone is the finest becomes a seemingly insignificant point.
Then - which stone is harder could become the more important point of interest of the two.

there is, no doubt, more to the story than just particle size - particle density being one major quality, followed by particle friability, shape, etc- and so on.

It really depends on one's definition of 'fine' and how it applies to Jnats.
But -as a baseline idea, hard and fine are two different things.

 

[Woodash]

Hardness: usually a function of i) thickness of overburden (degree of compaction); ii) particle size and particle size distribution (grading) and its effect on void space packing; and also iii) commonly dependent on the degree of cementation (commonly silica cement in the Jnats).

Fineness: principally a function of the particle size distribution (i) function of the original sediments and depositional characteristics, but can also be related to ii) post-depositional dissolution/recrystallization characteristics).

Hardness may or may not be related to fineness. Finer stones are commonly considerably finer than 2-3u in avg. particle size.

 

[Gamma]

Are you saying that you know of documentation stating that there are Jnats with abrasive particles finer than 2-3um?

 

[Bayamontate]

I had a LV 4 Shoubudani Namazu that was soft / thirsty than finished like a LV 5+ and a LV 5+ Nakayama Kiita that was hard with almost no feedback but finished like a LV 3. I guess my answer is, who knows. I read the 2-3 um thing somewhere and it made no sense to me in theory or application but what the hell do I know.

 

[alx gilmore]

Hardness: usually a function of i) thickness of overburden (degree of compaction); ii) particle size and particle size distribution (grading) and its effect on void space packing; and also iii) commonly dependent on the degree of cementation (commonly silica cement in the Jnats).

Fineness: principally a function of the particle size distribution (i) function of the original sediments and depositional characteristics, but can also be related to ii) post-depositional dissolution/recrystallization characteristics).

Hardness may or may not be related to fineness. Finer stones are commonly considerably finer than 2-3u in avg. particle size.

Steve
That was a very hard level 5+ explanation, full of information compacted into just a tight sentence space. I wish you could elaborate somewhat.
There is a Dorko waiting for you at the end of a string.


I have noticed that a very hard stone (selfish in giving up slurry) can mimic a very fine stone when the grit is bound so tight that under normal honing circumstances it stays in place and is not released into or as a slurry medium: i.e. the water medium remains clear and not colored or muddy. In this case we normally refer to this as a clear water stage as opposed to a slurry stage.

When using this type of noticeably very hard stone, as the blade engages the stones top surface, the steel edge glides from particle to particle only touching the exposed tops of the grit. But because the Jnat grit is friable, in this scenario the pointed particles tops are quickly cleaved while the remaining bound up portion of the particle in Sutu assume a flatter or more rounder exposed profile. If the sharpening session continues the less sharp or the flatter or rounded profile particles will continue to leave ever and ever shallower scratches. So in this way a shallow scratch is similar to a finer scratch because in each case the abrasive action and the visual effects imparted on the steel is kept to a minimum.

I do not feel that ultimately a shallower scratch has the intrinsic quality of a fine scratch, but instead a shallower acts only as a mimic of the finer scratch.

The comparative for the very hard stone in languid water honing session can be examined to some degree with a softer stone used under running water. The running water mechanically flushes away the released grit before it has a chance to affect the blade and before it has a opportunity to develop a slurry. The polishing effects are not as pronounced with the soft stone as with the hard, but the casual shiny bright look is well advanced beyond what the soft stones abilities would have been if the released particles were left on the stones surface to re-engage the steel in successive passes.

Alx

 

[Woodash]

Are you saying that you know of documentation stating that there are Jnats with abrasive particles finer than 2-3um?

I'm saying that at least one of mine is from having imaged it, and further, that even a garden variety shale is often dominated by particles <2u.

 

[Gamma]

Are you talking about the abrasive particles, or just particles in general?

See - I haven't been able to get a copy of the published 'report' that the Kyoto Whetstone Assn. referenced in their journal - the one where that study 'proved' that all Jnats have abrasive particles in the 2-3 um range, but I'd like to read it. Probably won't happen though - finding it would be one thing, getting it translated is another - so it looks like I'll just have to forget it.
Anyway - I don't buy into that claim being a solid factual piece of info - and I suspect that context plays into it the interpretation of the facts somehow.

 

[mainaman]

How does one measure fineness of Jnat abrasives when they are not spherical? Essentially there is no way to take any thickness measurement only rough diameter measurement of the particles?

Alex why is hardness of Jnats bothering you so much? Hard is good soft also can be good. When the stones are tested and work , then that is that.

 

[mainaman]

Are you talking about the abrasive particles, or just particles in general?

See - I haven't been able to get a copy of the published 'report' that the Kyoto Whetstone Assn. referenced in their journal - the one where that study 'proved' that all Jnats have abrasive particles in the 2-3 um range, but I'd like to read it. Probably won't happen though - finding it would be one thing, getting it translated is another - so it looks like I'll just have to forget it.
Anyway - I don't buy into that claim being a solid factual piece of info - and I suspect that context plays into it the interpretation of the facts somehow.

Those 2-3 um are the diameter size not the thickness of the grit. The thickness however will determine the actual fineness before and after break down.

 

[alx gilmore]

How does one measure fineness of Jnat abrasives when they are not spherical? Essentially there is no way to take any thickness measurement only rough diameter measurement of the particles?

Very good point, the grit in the Honyama stones looks more like a Kellogs Corn Flake and not like a ball or cube.

Alex why is hardness of Jnats bothering you so much? Hard is good soft also can be good. When the stones are tested and work , then that is that.

Stephen you are right, when the stones are tested and they work then all is said and done. I think that the qualities of all of the particular stones from the different mines used in razor honing are all open subjects for discussion. Hardness is just one aspect in a hone, and how it relates to ones abilities or what naguras they use or technique is of particular interest to me. Hardness is a narrow subject I admit, but from Arkansas to Coticules to Jnats the factor always pops up.

Alx

 

[Woodash]

This conversation would be a lot easier if we were talking only about coticule where the abrasives are more or less equidimensional. Really. With Jnats, you have a mixture of both platy and non-platy material - particle size of the latter is similar to what you would see if you sectioned the stone and looked via SEM or whatever. The former are clay minerals where the particles that you would see in a sectioned image are really showing you the area of the particle rather than it's actual 'fineness' as people tend to want to describe here. Particle size of this kind of stuff is sometimes described as 'effective spherical diameter' based on its settling rate which is one way that people sometimes measure particle size distribution (it's a fudge factor...).

So, in short, particle size per se is easily quantified in a stone like a coti, but much less so in a Jnat. It's not meaningless with a Jnat because even the relative size of (platy) particle should tell us a lot about the polishing capabilities of the hone, or its resistance to breakdown of the slurry, etc, but Jnats are complex and different (requires big fudge factor)! And that's part of their intrique and mystery! But it does all boil down to your own interpretation of how your stone works and what you're looking for in terms of performance, aesthetic, etc.

 

[Gamma]

I do think particle size has a big hand in the overall performance of Jnats - even though there is argument to the contrary posted on the internet.
Hardness has a few roles - one is to stay flat, the others involve how the slurry breaks down and how new particles are released throughout the honing process. One also might consider how it slurries with a Tomo Nagura something that hardness affects too. But - I don't agree that it's the bottom-line performance indicator.
But - that's just my take on it.