What actually is Hardness in natural stones, and how it affects sharpening

I have followed the Shoobie Doobie Asagi thread with great interest for weeks now, very nice stones shown here and there throughout and that thread as developed some great off topics. The topic of Hardness in Natual stones is universal and I do have some opinions about how it affects sharpeing that I would like to explore.

Sharpening is the act of removing steel, it is a grinding process that is used to create a geometrical profile to a blade. If a stone is not grinding it is not sharpening, period.

The hardness of a stone is the action at the stones very surface and it is all about the stones ability to shed particles from the stones surface during the sharpening process, period. All stones are hard, but their relative softness might be important also as an attribute.

I think it is overly complicated to merge synthetic stones and natural stone together in the discussion of natural stones, but to not recognize that some synthetic stones are hard or not is helpful in part because we here on this forum do use some of the same synthetics as others here do, so their names and numbers can be a jumping off point. But that is about as far as it goes in my opinion.

I know that some members would like to know if all Nakayama stones are harder than Ohira. This is not really a question with a logical answer as many will agree. Each natural stone is unique in itself, and even within one mine, any given strata will provide a wide varity of stone characteristics and hardness is one component that can vary slightly. And I further suggest that within any one mines history, the hardness of the stone mined can vary for particular reasons from one decade to another.

The hardness of a stone and a stones cutting abilities are related.

On the hardness side, if a stone does not shed dulled used grit particles, but instead retains those as bound up dulled grit particles on the surface, this is when the stones cutting speed begins to decrease and eventually halts. When it halts the cutting action, the stone action will only be that of polishing the blade, a burnishing effect, it will not continue to grind or remove steel. This is fine if you want a polished blade that looks shiny. As the glazing of the stone progresses I will suggest that the stone will continue to cut steel but with ever decreasing efficency and there will be a point in time when the cutting action actually stops. If you continue to rub the blade on the stone after this point other factors come into play as far as the metallurgy is concerned.

On the stones cutting abilities side, it must be recognized that not all stones are created equal, and as measured per weight some stones have a greater amount (per pound) of grit particles verses binder clays, while some stones on the other hand have less grit and a greater amount per pound of binder clays. The stone with more grit per pound will always have more cutting power if all other things are equal like surface hardness, grit size, etc.

If you an scratch a stone with a tool this is a crude type of proof of the hardness, the stone has in fact shedded grit particles. Incorporating a given force upon a tool with given and known characteristics, this simple test on a stone could be useful in rating stones as having a certain hardness. The closest entity we have on this forum to conduct this test are the various descriptions of hand pressure, and various qualities of tool steel in the from or shaving razors. This is a start. Alx

the way i look at hardness is through density the more compacted the stone is the hard the stone will be the harder the stone the less of a cutter but it will be a better polisher

trust me, it is not that simple

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Sharpening is the act of removing steel, it is a grinding process that is used to create a geometrical profile to a blade

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That is right, but what about polishing? There is evidence that at high grit ratings, the grinding action (ie. removing steel) gets less important.
Tha major action here is a plastic deformation, rather than grinding (even though always both is present). Grinding per definition involves removing metal at a fast pace,
wich is hardly what we want to do. I would suggest reading some of this, b/c we always think there is so little knowledge about sharpening
but indeed there is. But it is disguised :)

Grind - Wikipedia, the free encyclopedia
Polishing - Wikipedia, the free encyclopedia

and heres something reall special, quite in depth theory of the difference in polishing and grinding
Metallography, principles and practice - Google Books

And heres another one about polishing mechanisms
http://www.asminternational.org/cont...85G_Sample.pdf

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The hardness of a stone and a stones cutting abilities are related

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Maybe, but there are many exceptions to that rule. Not only is "hardness of a stone" still undefined,
but what I would call a very hard synthetic stone (the shaptons, 16000 or 30000 for example, or the pro 12000) may be extremely quick
at removing scratch patterns and cutting microbevels etc. The Shapton 16.000 is staggeringly quick and can (not should) be used after the Cerax 6.000 with a couple of circles.

My Shoubudani is it appears to me a harder stone than my Nakayama Kiita.
But it also appears to me that it is quicker.

So my prediction is that there won´t be any consens about what is hardness and how does it affect a stones performance.
There is too much to take into consideration

I have very little definitive knowledge about this topic. What little I know comes from a barber in Newark, NJ nearly 30 years ago, and my own hands on honing since then. He told me, when selling me a coticule, that the best razor hones are softer than harder. They would cut faster if they were soft, and you could tell if you dug into the edge of the coticule with your thumbnail and it left a mark.

Of course we can watch our water and see if the stone develops slurry merely from the honing action, or if we have generated a slurry with a slurry stone, how quickly the slurry turns color. This gives some indication of the speed of the stone's cutting power. I have tried the thumbnail test on a coticule or two but it doesn't really work for me. Is the mark I'm leaving caused by the coticule cutting my thumbnail or my thumbnail cutting the coticule ? Anyhow ....Attachment 73822Attachment 73823Attachment 73824Attachment 73825Attachment 73826

Then a couple of years ago I saw a yellow green Escher with two end labels. The first was the familiar "gelbgruhn", meaning yellow-green, and the opposite end had a label reading "guaranteed soft". I was very excited by this and was lucky to acquire the stone.

I already had the same stone without the guaranteed end label so after testing the stone and finding it equaled my y/g I sold it to finance some other craziness. I later regretted selling it, you can't have too many Eschers, and lo and behold lightning struck twice .... I found and acquired another. :y

So forgive me for cluttering your thread with photos of my prize, but I promised a friend to show some photos of it, and this is an ideal thread to insert them in. Note the last photo. There is part of an ink stamp on the honing surface indicating to me that the stone has never been used. A condition that I intend to remedy sooner than later. :)

lesslemming you are right about there is alot to consider when it come to stones when i think of hardness i try to keep it simple and think of density most of the time but not all of the time the harder the stone the slower it cuts but hardness has nothing to do with speed of cutting its what the stone is made of the "cutting agent" (and speaking of only natural stones because synthetic's are a different animal) take the ark stones their made of microcrystalline quartz once you start honing on the stone the quartz wears down flat it doesnt break apart it gets smooth and flat jnats are the completely different you could have two jnats from the same mine same hardness one having su and one w/o the one with su will cut faster like you said its alot to think about

Alex, thnx for the post.

Could you explain why some very hard stones
still have very good cutting abilities whereas
other hard stones are very slow? I know you
wrote that depends on grit per pound, but
what affects this?

The scratch test makes sense.

Basically what I would do, is I would hold the stone
in my hand to check its weight/density. Then I would
knock on the stone to listen what kind of sound it makes.
I assume a soft stone would make a duller,lower sound
whereas harder stones a more ''ping'', higer pitched sound.
Next thing I would do is sharpen on the stone, if I feel that
the surface of the stone is very hard(indentation wise, no
scratching ability), then I would think ''man this thing is like
glass!'' and conclude this is a hard/very hard stone.

Sharpman

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Originally Posted by Lesslemming

Maybe, but there are many exceptions to that rule. Not only is "hardness of a stone" still undefined,
but what I would call a very hard synthetic stone (the shaptons, 16000 or 30000 for example, or the pro 12000) may be extremely quick
at removing scratch patterns and cutting microbevels etc. The Shapton 16.000 is staggeringly quick and can (not should) be used after the Cerax 6.000 with a couple of circles.

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Yes, but the Shaptons are synthetic stones. They are still quick,despite being
hard, because they are loaded with grit particles. If a fine and hard stone is very
quick that either means the particles are very hard(think diamond)or the stone
has a lot of sharpening particles per square unit or both. Might be wrong though.

Sharpman

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Originally Posted by SharpMan

Alex, thnx for the post.

Could you explain why some very hard stones
still have very good cutting abilities whereas
other hard stones are very slow? I know you
wrote that depends on grit per pound, but
what affects this?

The scratch test makes sense.

Basically what I would do, is I would hold the stone
in my hand to check its weight/density. Then I would
knock on the stone to listen what kind of sound it makes.
I assume a soft stone would make a duller,lower sound
whereas harder stones a more ''ping'', higer pitched sound.
Next thing I would do is sharpen on the stone, if I feel that
the surface of the stone is very hard(indentation wise, no
scratching ability), then I would think ''man this thing is like
glass!'' and conclude this is a hard/very hard stone.

Sharpman

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checking for hardness do the water test put one drop of water on a few of your hardest stones which ever stone holds the water the longest is the hardest

Jimmy,

That stone is amazing, you really are lucky to find one that NOS. The one I have from you is amazing, I love it, I hug it in my sleep at night.

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Originally Posted by eleblu05

checking for hardness do the water test put one drop of water on a few of your hardest stones which ever stone holds the water the longest is the hardest

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Wouldn't holding water longer be a matter of density ?

BTW, my posting the Escher seen above, within this thread, was due to the label "guaranteed soft." I think the relevance to this thread is demonstrated by Escher finding guaranteeing softness for a razor hone, which is what Eschers were/are, an important enough selling point to print and apply a special label noting that characteristic.

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Originally Posted by JimmyHAD

Wouldn't holding water longer be a matter of density ?

BTW, my posting the Escher seen above, within this thread, was due to the label "guaranteed soft." I think the relevance to this thread is demonstrated by Escher finding guaranteeing softness for a razor hone, which is what Eschers were/are, an important enough selling point to print and apply a special label noting that characteristic.

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yes the denser the stone the harder the stone is. if the water gets absorbed into the stone that means the stone is porous not as dense as the other stone holding the water on top of the stone

Quote:

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Originally Posted by JimmyHAD

Wouldn't holding water longer be a matter of density ?

BTW, my posting the Escher seen above, within this thread, was due to the label "guaranteed soft." I think the relevance to this thread is demonstrated by Escher finding guaranteeing softness for a razor hone, which is what Eschers were/are, an important enough selling point to print and apply a special label noting that characteristic.

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Jimmy I am with you here.
I have been thinking about it for a while and I am not sure the water drop test is actually that indicative.
Example Escher, it is considered soft but it holds no water at all, it is just the binder is not hard compared to some Jnats.
On another hand I feel like the harder the stone the more compact it will be and thus the less water will it absorb. In this light water drop test will show that the hardest stone releases water the fastest. If anyone knows how to explain the test please do so.

the denser the stone the less water it will absorb density = hardness the porous the stone the more water it will absorb

It seems to me that hardness would have more to do with the mineral composition of a stone than the density.

Maybe I'm not thinking of hardness the right way though.

That is why I repeat: there is no definition of hardness of a stone. Why should there be?
What could be the benefit of a unified hardness system for naturals?

BTW I had very hard and very quick coticules.
It remains difficult to find a definite consens for naturals

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Originally Posted by Lesslemming

That is why I repeat: there is no definition of hardness of a stone. Why should there be?
What could be the benefit of a unified hardness system for naturals?

BTW I had very hard and very quick coticules.
It remains difficult to find a definite consens for naturals

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I too have a coticule that is extremely hard (a La Verte), but also is fairly fast on water. It's speed on slurry is on the slow side, but on water it catches up quick. Interestingly it is also the only coticule I have that leaves an edge that I can get weepers with, similar to a thuringian edge if I'm not careful, yet my thuringian I would describe as soft.

Trying to relate hardness of a stone to the edge it gives for naturals I think would be in vain, as there really is no uniformity IME.

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Originally Posted by SharpMan

Alex, thnx for the post.

Could you explain why some very hard stones
still have very good cutting abilities whereas
other hard stones are very slow? I know you
wrote that depends on grit per pound, but
what affects this?

The scratch test makes sense.

Basically what I would do, is I would hold the stone
in my hand to check its weight/density. Then I would
knock on the stone to listen what kind of sound it makes.
I assume a soft stone would make a duller,lower sound
whereas harder stones a more ''ping'', higer pitched sound.
Next thing I would do is sharpen on the stone, if I feel that
the surface of the stone is very hard(indentation wise, no
scratching ability), then I would think ''man this thing is like
glass!'' and conclude this is a hard/very hard stone.

Sharpman

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Hi Sharpman
Without actually trying out the particular "hard stone" I would venture to guess that some hard stones do cut very fast at first because they are loaded with grit. But if the swarf from the steel blade is not carried away in some manner, the stone will become loaded with compressed cleaved grit particles that are essencially welded into the voids of the stones surface along with ground off steel. This glazed stone will at this stage stop being a hone but more like a burnishing plate. Here again some people think that a bright shiny blade must be sharper, but I suggest that the metallurgical changes necessary to polish a blade a blade by burnishing will have mixed consequences including destruction of the temper of the steel maybe by a few points, and an ultra thin but very fragile edge that will only last a few shaves at best.

My Shapton 30k on glass becomes black when I use it, the grit is so sharp and the action is so fast and the stone so hard that the black metal filings just have no where to go but to fill up the surface voids of the stone. Do I just continue to use a stone that was pure white but is just becoming blacker and blacker? Or should I lap the stone to clean off the swarf and in doing so reveal fresh grit? When does the 30k start acting like a burnishing plate?

Also I like your idea of testing the hardness, totally sensual and empiric and based on observation. And the ping of a stone will deduce consistancy and reveal any imperfectons. The water test has some cautions with japanese stone. Some miners coated the top surface of freshly surfaced stones ready for market with an eggwash to prevent the soiling of the surface with grime and dirt. And also I have found that Jnats will over time from a natural oxidized film that is microns thin, both of these issues will imped water. So unless the stone is lapped, but with a used stone the water could be uses as an indicator. I have to agree that a dense stone will be more compact and will shed water more easily than a porous (more voids between physical particles) but also a dense stone may be less porous because of a high concentration of binders.

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Originally Posted by Lesslemming

That is why I repeat: there is no definition of hardness of a stone. Why should there be?
What could be the benefit of a unified hardness system for naturals?

BTW I had very hard and very quick coticules.
It remains difficult to find a definite consens for naturals

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Lesslemming. Maybe we do not need a hardness test or scale. If you could arrange and enforce the use of the word "hard" on this forum, then we would not. But as it stands almost all posts comment in some way about how hard this or that stone is. I myself do not feel that the hardness of a stone should be forefront, to me the imparitave is the cutting qualities of a stone. 20 strokes on a slightly softer stone does more for me than 100 strokes on a harder stone if the grit particles sizes are equal. And if sharpening is the goal, the blade is less distorted with the fewer strokes.

Also I think that Dr. Naka uncovered a unique answer as to why some edges are more comfortable than others. His description of Iwasaki-sans using his hands to describe the profile shape of a finished blade, all finger tips touching and both palms together, with fingers straight or with fingers bowed. The bowed being more comfortable for softer skinned beards. A slightly rounded blade profile. The perfectly straight flat profile may be sharper but usually harsher. A softer stone will aid with its free roaming grit to provide this splayed profile, the harder stone will provide a flat profile. Alx

P.S. I did not mean to use the term grinding as in coarse grinding or gross removal, but instead to mean just the mechanical act of steel removal at all or any grit levels. a

Yep i think too that there are different prefferents on the edge, coticule is a lot coarser then a Jnat but still shave very nice and sometime better, the hybrid coticule that i have is a lot harder then my Ozuku but stil bit coarse but shave is super nice like any jnat !

For hardnes there are a lot of different stones and hardnes and you cant prove them all i have a Okudo suita that is lv 5 hardnes but lv 2 fines, so you cant realy comper hardnes on Jnats or others natural stones you just have to try them and give approx value on fines and hardnes and what they have to be used for :) there is not realy right answer here !! Becouse they are all different !!

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Originally Posted by maxim207

:) there is not really a right answer here !! Because they are all different !!

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Well said Max. I was just thinking about this today. I don't get hung up on one particular stone, because they're all good for something. Variety...

Hence, HAD....

This is a very complex subject. How well the stone cuts is dependent on so many things. The minerals the rock is comprised of, the kind of rock, the density, the particle size and shape, the mix of minerals in the rock and how they are mixed, and a host of others. Remember that running water is the best cutting force there is. It formed the Grand Canyon and can polish a rock to a mirror effect.

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But as it stands almost all posts comment in some way about how hard this or that stone is

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As far as I could make out the statement of hardness always stands in comparison to other stones of its kind.
"My Coticule is fairly hard" could mean "For a coticule mine is fairly hard"

I don`t think people actually take their Ohzukus into consideration when deciding if their Coticule is a soft one or not.
They compare it to others, or express their opinions. Hardly ever has there been a cross referencing.


I believe hardness is an information that can not stand alone. It is much more interesting to know, and tells a bit about the feel the stone should provide than about the performance

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And if sharpening is the goal, the blade is less distorted with the fewer strokes.

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Well, that depends! If your technique is good, you can do 100 or 200 laps on a slow Chinese without disorting the edge.
It is not recommended to do much more than necessary

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to me the imparitave is the cutting qualities of a stone

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The cutting quality of a stone is highly dependend on the very nature of the stone.
That´s why you can find hard and coarse, soft and fine, quick and fine, quick and hard stones across the universe.
Hardness is of no value unless it stands in bulk with the rest of the information.
It is a bit like saying the weight of a Car defines how fast it will go.

Well that may be true in some cases, but obvioulsy there is way more to take into consideration

For razors we ussealy talk about polishing stones and only final polish, not realy sharpening !!
Thats why i like coticules a lot they sharpen and polish very greate and i use them a lot my self, but if you take Ozuku or Thuri they are ONLY for final polish and coticule can not get that kind of polished edge !
You can get some prepolishers Jnats in same grit range as coti, but they are bit slow for razors, and some very fast ones is super expencive.

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Originally Posted by thebigspendur

This is a very complex subject. How well the stone cuts is dependent on so many things. The minerals the rock is comprised of, the kind of rock, the density, the particle size and shape, the mix of minerals in the rock and how they are mixed, and a host of others. Remember that running water is the best cutting force there is. It formed the Grand Canyon and can polish a rock to a mirror effect.

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true.... and a blade of grass can crack the strongest concrete...

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Originally Posted by alx

If you an scratch a stone with a tool this is a crude type of proof of the hardness, the stone has in fact shedded grit particles. Incorporating a given force upon a tool with given and known characteristics, this simple test on a stone could be useful in rating stones as having a certain hardness. The closest entity we have on this forum to conduct this test are the various descriptions of hand pressure, and various qualities of tool steel in the from or shaving razors. This is a start. Alx

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Maintaining a flat bevel geometry while sharpening for me is not as crucial with a razor as say a gouge or a plane blade. From discussions I have had here coupled with the fact that so many great shaves are accomplished from so many methods where flatness in not considered makes me think. An accomplished sharpener knows from experience that a harder stone will not deform and round the bevel. With the light pressure used in finishing up a razor, I wonder how stone hardness applies?
I have accomplished great edges happen on stones like the Nakayama from you which happen to be hard. Eschers also give me great results and as Jimmy noted they are considerd soft? Good food for thought, thanks:)

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Originally Posted by Kingfish

I have accomplished great edges happen on stones like the Nakayama from you which happen to be hard. Eschers also give me great results and as Jimmy noted they are considerd soft? Good food for thought, thanks:)

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I used to fish a lot & there were always people arriving for the run in tide & those for the run out tide. They all caught fish but disagreed with each others beliefs about when to fish :confused:
When you're talking about 10-15 finishing strokes with no pressure will an Escher give a better edge than an Asagi or vice versa ??? I think there's a lot more to it than hard vs soft.

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Originally Posted by Kingfish

Maintaining a flat bevel geometry while sharpening for me is not as crucial with a razor as say a gouge or a plane blade. From discussions I have had here coupled with the fact that so many great shaves are accomplished from so many methods where flatness in not considered makes me think. An accomplished sharpener knows from experience that a harder stone will not deform and round the bevel. With the light pressure used in finishing up a razor, I wonder how stone hardness applies?
I have accomplished great edges happen on stones like the Nakayama from you which happen to be hard. Eschers also give me great results and as Jimmy noted they are considerd soft? Good food for thought, thanks:)

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Hi Kingfish
I am on the same bevel with you as far as plane blades are concerned which traditionally are based on flat bevel configuration. Razors are also requiring flat bevels, but currently there are custom and finely tuned bevels that go beyond what most tool users require or consider. Razors edges are immediately critisized by their users as they tug on our skin, edges tug because of improperly formed bevels which converge poorly or intermittently. Shaved wood boards do not talk back with swear words.


Granted, hard stones will not so easily round a blade in part because the stone itself dishes more slower, but a faster cutting softer stone will dish to the same small degree if the same amount of actual sharpening (bevel formation) is done with fewer strokes. Here is a scheme I worked out a few years ago to compare stone hardness. I used the same blade to test each stone using the same amount of hand pressure, length of stroke and water.

So you can see by the black swarf in the water and slurry that with a faster cutting stone using fewer strokes you can remove the same or equal amount of steel. Now this is useful if you are actually sharpening a blade. If you are just polishing a blade to make it shiny then any hard stone or maybe even glass or would work.

www.thejapanblade.com/hard203.jpg

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Originally Posted by alx

Hi Kingfish

Granted, hard stones will not so easily round a blade in part because the stone itself dishes more slower, but a faster cutting softer stone will dish to the same small degree if the same amount of actual sharpening (bevel formation) is done with fewer strokes. Here is a scheme I worked out a few years ago to compare stone hardness. I used the same blade to test each stone using the same amount of hand pressure, length of stroke and water.

So you can see by the black swarf in the water and slurry that with a faster cutting stone using fewer strokes you can remove the same or equal amount of steel. Now this is useful if you are actually sharpening a blade. If you are just polishing a blade to make it shiny then any hard stone or maybe even glass or would work.

www.thejapanblade.com/hard203.jpg

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I definitely see what you are saying from the pics. Softer stones from the selection you have get the job done much quicker. Of course that is contingent on many other factors being equal in terms of quality, etc.

I never would be happy if a Jnat could only polish. I expect way more than that from a Jnat, that is why I kept the stones you sent me!

Wow this is one fine thread!

One way to explore this is to try and
sharpen butter and cheese.

Some tools shave off curls some tools
smear the surface or gather a lump.

Steel like butter can be brittle (when cold)
or soft and malleable (warmer)....
Compare and contrast a soft cheese
with a hard cheese like Parmesan and
all the ones in between.

Then explore hardness tests... take
a marble and "measure" how it dents
the cheese with pressure.

The hard Parmesan cheese is interesting because
it shows "micro chipping" and also has salt
crystals.

The obvious thing missing
in my cheesy analogy is work
hardening. Work hardening can be key
to the shave-ability of many steels and has
applicability to final stropping.

I was just reading this thread again, very interesting points.

I only have 4 natural stones. A takashima karasu, an okuda suita, a nakayama
namito(I guess,got it from mainaman) and a chinese guangxi hone. When I tap
all stones:

-the okudo doesn't really give a high pitched voice, the others do.
The okudo also feels softer and produces easier slurry.

-The karasu, namito and guangxi are close in hardness. All three give high pitched
sound. They give their slurry very slowly.

Then I tried scratching one stone with another.

1)The karasu did not really create any scratch on the chinese guangxi hone(CGH) and
vice versa. My conclusion, both stones are about the same hardness.

2)Used the namito to scratch the karasu and it did. The karasu could not
scratch the namito. The namito also scratched the CGH.

Conclusion, the namito is the hardest. This is hardness based on the scratch
test, feel of the stones and the sound they give when tapping the stones.
A clear caveat is of course that the sound given after tapping has to do with
the size of the stone.

The scratch test is confusing for me because I would guess the sharpening particles
in all japanese stones have the same hardness. It's just the how tough the binder
is and how much compression there is that AFAIK defines hardness in these stones.

Sharpman

Maxim wrote:

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Yep i think too that there are different prefferents on the edge, coticule is a lot coarser then a Jnat but still shave very nice and sometime better, the hybrid coticule that i have is a lot harder then my Ozuku but stil bit coarse but shave is super nice like any jnat !

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I was always under the impression that your ozuku was the hardest stone you had. LV 5+++ you wrote on time. The coticule must be LV 6 lol. Interesting to see that harder does not mean finer even in natural stones.

When it comes to hardness I've always took it into account but its always been a lesser factor in determining cutting power IMO.

I have two coticules; a la verte and dressante. The Dressante doesn't leave a hint of a mark with the nail test but is a quick cutter and finisher but its a hard coticule. The la verte is very hard but quicker on water and easier to finish, so how that gets explained I haven't a clue.

I would go with the amount of mirror the surface of the natural hone creates when lapped and refined. In order of surface mirror from least to most noticeable of my hones; dressante, BBW, la verte, jnat, which correlates with how easy, sharp and how much of a polished bevel I can get off each hone. I would say the jnat is the sharpest for me but by a milidegree from my coticules, some are easier to get an edge but as with all natural hones its how you use them.

Remember that when we usually refer to hardness its with minerals which are relatively homogeneous substances. Most honing stones are rocks which are combinations of minerals so in one honing stone you may have minerals contained within, that range from a hardness of 4 or 5 up to 8 or nine (for example) and each mineral making up varying percentages of the rock.

Coticules act a lot different then Jnats so it is very bad comparison.
In general i will say harder Jnats give better edge on razors, but of course there are exceptions.
Lets say it like that, maybe 2 out of 30 softer stones i find good for razors
For harder stones it is 28 out of 30 that is good.
But its also really depend what you like and how you like your edge.

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But its also really depend what you like and how you like your edge.

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I think your right maxim, I think how you get to that edge also matters with natural hones. How sharp an edge can get and how long and easy it is to achieve are big factors for me, but then that depends on the users skill and experience, If I had a natural hone that was soft but was easy to achieve a very shaveable edge, I would be more than happy with it.

The jnat that I bought from you is a very easy jnat to hone on and gives great edges which I'm sure I haven't maxed out even yet.

With Naturals It all comes down to perspective... A 'fast' jnat may be just 'medium' to another user and because there is so much variation in naturals, it confuses it even more. The experienced users of the stones have a better view of the whole spectrum of stones like yourself maxim with jnats or Bart regarding coticules.

I have only ever used 1 jnat and two coticules so can only describe them in comparison with each other, so when it comes to speed I talk in minutes of honing, but as a user becomes more experienced, other factors like feel, ease of honing, aesthetic qualities and learning curve come into play with naturals I think. How hard a natural hone is - as you mentioned - is more important on jnats than on coticules as coticules seem to show no correlation between speed and how hard the coticule is.

You really can't compare a Coticule, an Escher or J nat. They're different stones, and impart different edges. We don't really assign grit ratings, because they're naturals, but we guesstimate. The Coti would be the lowest, Escher in the middle, and J nat the highest (at least for the most part)

I was reading through this thread again, and saw the fingernail test. I still use it today, mostly on Coticules, If you can see the scratch, it's a soft stone, If you can't, it's hard. When you have many stones, and have seen different results, this test makes more sense. Now, with Coticules, I have always found softer ones, to be better cutters, and the harder, usually greenish to pale yellow to be better finishers. IME. YMMV.

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Originally Posted by zib

You really can't compare a Coticule, an Escher or J nat. They're different stones, and impart different edges. We don't really assign grit ratings, because they're naturals, but we guesstimate. The Coti would be the lowest, Escher in the middle, and J nat the highest (at least for the most part)

I was reading through this thread again, and saw the fingernail test. I still use it today, mostly on Coticules, If you can see the scratch, it's a soft stone, If you can't, it's hard. When you have many stones, and have seen different results, this test makes more sense. Now, with Coticules, I have always found softer ones, to be better cutters, and the harder, usually greenish to pale yellow to be better finishers. IME. YMMV.

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It might just be my deceptively hard and fast stone thats strange, its a bugger to finish on compared to the la verte, oh well

First of all, regarding most of the best or favourite or expensive naturals, there are no quarries left. The softer stones are the ones that disappear before the hard ones for obvious reasons. And soon people forget that a magnificent quarry had soft and hard stones, thinking that they where all hard ones( for example, I haven't seen many light colored Thuringians the last years, but the dark ones are plenty). The older the quarry, the most likely the softer of those stones are not around anymore. Second, honing a razor or whatever with a soft stone and no pressure, is like honing it with a hard stone applying more pressure. And the pressure we apply is a mysterious thing. If we use the weight of the razor on an escher, we get a nice shaving. Can we decrease this pressure? This way, we could get an even better shave. For me, that's the difference between a hard and a soft hone. Both have their abrasives and their binding material. The binding material and its hardness has nothing to do with the size of the abrasive particles.

(......The binding material and its hardness has nothing to do with the size of the abrasive particles.)

No, maybe not however the hone is a total package and the binder comes in contact with your razor and contributes to the overall hone quality.

This man Vasilis has opened an important door, I think he is on to something.alx

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Originally Posted by Vasilis

First of all, regarding most of the best or favourite or expensive naturals, there are no quarries left. The softer stones are the ones that disappear before the hard ones for obvious reasons. And soon people forget that a magnificent quarry had soft and hard stones, thinking that they where all hard ones( for example, I haven't seen many light colored Thuringians the last years, but the dark ones are plenty). The older the quarry, the most likely the softer of those stones are not around anymore. Second, honing a razor or whatever with a soft stone and no pressure, is like honing it with a hard stone applying more pressure. And the pressure we apply is a mysterious thing. If we use the weight of the razor on an escher, we get a nice shaving. Can we decrease this pressure? This way, we could get an even better shave. For me, that's the difference between a hard and a soft hone. Both have their abrasives and their binding material. The binding material and its hardness has nothing to do with the size of the abrasive particles.

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