Honing on extremely hard jnats

[rhgg2]

Hi all,

I am interested in general thoughts on honing on extremely hard jnats. I have had success finishing razors with various other jnats from medium hard to very hard, but so far have only succeeded in producing slightly undercooked edges on extremely hard jnats. There are two aspects to the technique required, mechanical and logistical. Mechanical skill I just have to learn but in terms of structuring the honing on an extremely hard jnats I am still trying to figure out what the fruitful approaches might be. Of course this will vary from stone to stone but I am hoping to hear about general principles.

On average, the grit from the extremely hard stone should be finer, but the question is how best to access it. The hardness means that (1) tomo slurries will tend to be largely tomo and (2) the stone cuts a lot more slowly. (2) could just be because my extremely hard stones are not very grit rich but regardless they are I think by their nature going to cut more slowly.

I have experimented with a few options:

(i) use a softer but very fine tomo.This kind of works, but I don't like it, as the base stone is not really bringing anything to the party.

(ii) use an extremely hard tomo and suck up the fact that it's going to take like 5 minutes to raise a slurry.

(iii) take an edge which is already well finished to it, and raise a very thin slurry, just enough to provide lubrication, and sit on it for ages so the base stone has time to get somewhere. (Sort of treat it like an ark).

I have not yet had much luck with (ii) and (iii) and am going to keep trying, but wondered if there are other fruitful approaches to explore.

 

[Christian1212]

I would just take edges that are ready for the final finishish to the hard jnat with tomo slurry. Matching tomos can be weird but just have to try them all. On my hardest stone I can use my hardest tomo but usually go with a very fine slightly softer tomo. I am using only weight of the blade at this point.

My go to progression for the dream edge is asano naguras on a hard full size jnat. This jnat though does not finish where I want so then I use tomo on my nicest jnat for the final finish. Usually that gets the edge where I want it, however an additional tomo session on the final stone has never hurt me.

While I don't use DMT slurry often, it can be used to compare 2 stones. Using a light DMT slurry to finish on 2 hard jnats will give a decent idea of how they finish compared to each other. While a smoother surface will make both of these edges better - diamond slurry let's you compare the stones with close to the same surface prep, and slurry from base stone only. Just know if any diamonds get in the slurry though you will have to set up the razor/stone again.

 

[JPO]

Have you tested that your stone has enough abrasive cutting power to work well as a razor grade stone?
You can try generating some diamond plate slurry and use a knife or a plane blade just to test if it is cutting well.

The stone does not need to be fast to be a good razor stone, but i would not spend allot of time trying to make it work if it is just a marble feeling stone without abrasive qualities.

(i) use a softer but very fine tomo.This kind of works, but I don't like it, as the base stone is not really bringing anything to the party.

I think you need a good tomo with allot of abrasive cutting power for this to work well. Sometimes the slurry is just polishing the stones surface, and you are predominately using the slurry to cut. If your other naguras did a good job you should be able to get a good edge, but it takes some more time.

(ii) use an extremely hard tomo and suck up the fact that it's going to take like 5 minutes to raise a slurry.

If you want to speed up this process you can lap your stone. Rinse of the slurry and then generate your tomo slurry. By doing this the stone will release more abrasive into the slurry. You still need to spend some time with the tomo to recondition the surface a little.
One alternative is to generate some slurry with a diamond plate and use your hard tomo to brake it down.
It will also depend on how much work you are doing on the final tomo.
Before tomo slurry i usually use a koma. So, for me it makes more sense just to spend a little extra time generation the tomo slurry. It also helps if you don't have allot of water when you generate the slurry.

(iii) take an edge which is already well finished to it, and raise a very thin slurry, just enough to provide lubrication, and sit on it for ages so the base stone has time to get somewhere. (Sort of treat it like an ark).

If the stone is good you should not have to spend allot of time on on a "already well finished " edge.
This will in most cases just create a unstable overcooked edge.
If i jump from something like an 8k, i don't need to spend allot of time on a jnat.
I generally have better results if i jump from a 5-6k, and spend more time with different slurries.

Some stones are just more suitable for tools then razors.
The really good razor grade stones i like is super hard but feels soft in use. So, super hard stones does not need to be difficult to use, but those that feel like marble without much abrasives in them is probably also common and might not be worth spending too much time with.

 

[lightfoot]

I think part of the problem with natural stones is the whole concept, idea, and backstory that comes with that particular natural stone variety. If you’re bringing a razor that isn’t quite shave ready to a Jnat for example then I generally focus on getting the edge to that shave ready point rather than thinking about the backstory from working on a particular stone variety and Tomo combination for example although these things obviously factor in. In other words I’m thinking about whether or not the Razor is sufficiently thin at the cutting edge for the bare minimum of being “shave ready”. Once I am at that point then I think about the following work being related to the comfort level or face feel.

In other words while I’m trying to get to that shave ready stage I’m thinking about “shaping” or thinning the edge first and foremost as opposed to what kind of stone I’m working on. As long as the stone is appropriate for the stage of work I’m focused on the Razor and not the stone.

 

[Herrenberg]

I've done a fair amount of finishing on very hard JNats, including one that seems off the charts. They can make some really nice edges.

The geometry of the bevel must be perfect, or you can get some nasty skipping and vibration, which can cause damage to the edge.

I've not found just water to work well; not enough lubrication. I use slurry generated by a very worn-out diamond plate. As long as there is a reasonable amount of slurry in there, I don't have problems.

These stones are hard enough that nagura of any sort are not a reasonable option.

I had some nice results by soaking one for a couple of hours, which made it noticeably more tractable, although certainly not soft. I plan to experiment with this more. It probably carries risks (I'm imagining water getting into unseen structural flaws and breaking down the stone, however unlikely that seems at this hardness), so I'm only going to do it with one of my stones.

 

[SliceOfLife]

I've got one or two stones that are mystery stones; but which I think are jnats based on the markings and other similarities to other stones I've owned that would qualify as great, easy to use finishers.

My first Jnat was a crazy hard Karasu from MMJP on ebay... I used it on and off for a few years when I was starting out with Razor honing before shipping it off, to David I think. It gave good edges and didn't seem to have anything toxic in it; but I remember it being quite slow and in the end I don't remember it giving me anything I've been unable to reproduce with much faster stones since, other than being pretty. I had also bought a bunch of cheap 330mate stones and other stuff like the $60 honyama from one of the reputable sites/etc. Most of them felt like prefinishers to me. Shaveable... but really why bother. One or two of the 330mates were decent finishers; but again slow and nothing special.

Around the same time I kind of stepped back from the Nagura and the whole Jnat progression as well. Now I just use Jnats the same as any other finisher... and I wouldn't say that an ultra-hard is necessarily any better or worse than softer ones; as long as they are fast... and so the Jnats I've kept around have all been faster examples in that finisher to great finisher range... and with stones like that; they fit my honing method without any fancy strategies; worrying about slurry or nagura or progression. And I don't think I'm alone; because almost every provably vintage Jnat I've bought is like this. Every eBay vendor claims their rocks are from 1950's or before and from XYZ popular mountain... but the rocks I've actually gotten stuck to vintage hardware (for razors or presumably Kannas) are ALL fast and easy to use. The more modern ones are more mixed. Some great, some good, most pretty unexceptional. Which may be how it goes; since I'm not willing to drop $400 on a Jnat; so I'm most likely buying the stuff that doesn't cut it as a top notch stone when I buy modern stones.


TLDR: I've had some very hard Jnats I bought from a few different eBay vendors... and they're definitely harder to use than softer ones. I've also got some vintage mystery stones I THINK are Jnats that are similarly hard and aren't really any harder to use... but I can't say 100% they are in fact Jnats.

Consequently; I suspect that hard, fast, easy to use Jnats are pretty rare and command a premium enough price; I'm not the type of customer buying them. They surely exist; but maybe those are the stones that are like 8x3x2" and listed for $1500 on eBay that I scoff at?

 

[rideon66]

These super hard JNATS are why Mikawa nagura became popular on jnats. The other options are Atoma plate, a softer Tomo nagura or a really hard Tomo nagura and spend sometime making slurry. All these options can work depending on the base stone that is.

 

[rhgg2]

Thanks, all!

I think the edges I am taking in are okay geometry wise as I don't experience skipping or chattering. Even plain water seems workable (though I don't think helpful) so long as there is not too much water.

There is always the question, is it the stone or is it me. My intuition is that in this case it is a bit of both. I think all the extra hard stones I have are a bit slow. So I don't necessarily expect the best possible edges from them, but I'd like to make the best edges they are capable of. I find it more motivating to make an unsatisfactory edge than a superlative one because I am stubborn and refuse to admit defeat to a bit of stone.

I am going to try again with a very hard tomo and/or DN and see where I can get!

 

[rideon66]

One thing I find on really hard stones that works is finishing on light slurry with the lightest of lap. Like floating the edge. It takes time and patience, but gets easier and faster with practice.

 

[Herrenberg]

One thing I find on really hard stones that works is finishing on light slurry with the lightest of lap. Like floating the edge. It takes time and patience, but gets easier and faster with practice.

Exactly this.

 

[Steve56]

The hardness means that (1) tomo slurries will tend to be largely tomo and (2) the stone cuts a lot more slowly.

This is true most of the time but not always. Hardness isn’t the only factor in play here, the abrasiveness of the base stone and tomo is significant. I have hard stones that will produce tomo slurry even from hard tomo and visa versa. These very abrasive stones are less common but they do exist.

(ii) use an extremely hard tomo and suck up the fact that it's going to take like 5 minutes to raise a slurry.

This works but is a PITA. Keep both stones deglazed with a worn diamond plate and life is easier.

(iii) take an edge which is already well finished to it, and raise a very thin slurry, just enough to provide lubrication, and sit on it for ages so the base stone has time to get somewhere. (Sort of treat it like an ark).

Try diamond plate slurry, it’s easier to generate a heavier slurry and diamond plate slurry is usually faster. You can also ‘break’ diamond plate slurry with your hard tomo.

Good honing!

 

[H Brad Boonshaft]

What is the condition of the bevel and edge when you go to this Jnat?

Is this a condition with all razors or just one? With all razors for optimum performance, you must match the steel to the stone.

Hard steel soft stone, soft steel hard stone.

If your razor has an edge, 8-10k by adding too much slurry you may be edge dulling. Try finishing with water, 10 laps dunk, 5 laps dunk, 2 laps dunk, 5-6 single laps dunk after each lap. Or under running water.

Hard stones are stone face dependent, like Arks you have to find that sweet spot of stone face finish. So, a stone lapped with a 300-400 diamond plate will finish differently from the same stone finished to 1k diamond plate then finished again, polished with a tomo nagura and slurry rinsed off for honing. And sometimes stones load up and get clogged, lap with a 3-400 plate to cut a new surface/face.

Experiment with stone face finish. Try Diamond slurry of different grits and finish on water.

As Steve said and you don’t hear talked about much, “You can also ‘break’ diamond plate slurry with your hard tomo”. An excellent technique.

Using a nagura is not just about making slurry, it also surfaces the stone, and if worked properly can refine the slurry. If you make too much, just wipe off half of the slurry with a clean sponge.

If your bevels are flat and you are honing all the way to the edge, slurry impact may be dulling the edge.

Match the stone to the razor and match the slurry/nagura to the stone/razor.

 

[rhgg2]

This is true most of the time but not always. Hardness isn’t the only factor in play here, the abrasiveness of the base stone and tomo is significant. I have hard stones that will produce tomo slurry even from hard tomo and visa versa. These very abrasive stones are less common but they do exist.

That is interesting. It is actually the case that some of my mikawa nagura, although rather soft, make a slurry has a shade of base stone colour, even on pretty hard stones. When I saw this I thought it meant I'd overestimated the hardness of my base stone but from what you say it may actually because the nagura is highly abrasive.

 

[Steve56]

That is interesting. It is actually the case that some of my mikawa nagura, although rather soft, make a slurry has a shade of base stone colour, even on pretty hard stones. When I saw this I thought it meant I'd overestimated the hardness of my base stone but from what you say it may actually because the nagura is highly abrasive.

Could be, some shiro nagura are grit rich. I’ll try to post an image tomorrow.

 

[Steve56]

OK here’s an image of about equally hard stones not raising equal slurry proportions. The asagi is extremely abrasive. You can partially see the kiita tomo, it’s one of @alx gilmore stones and he might remember it, he still has the other end of the stone!

 

[Gamma]

Hi all,

I am interested in general thoughts on honing on extremely hard jnats. I have had success finishing razors with various other jnats from medium hard to very hard, but so far have only succeeded in producing slightly undercooked edges on extremely hard jnats.

I hone almost exclusively on super hard Jnats.

Hardness is only one part of a very big equation. Hardness does not equal quality. It just equals hard. And there are many qualities of hardness to know about. You can have hard and porous. You can have hard without wear resistance. You can have hard and super dense and no abrasive. And so on.

The HGAL system, for example, cites 4 points of interest to gauge a stone. The system is, essentially, useless though, due to subjectivity and no realy standards of qualification. Best you can hope for is for one seller to gauge everything the same, but don't try to match one sellers numbers to another. Then you have the sellers that lie about everything and just make stuff up and then you're stuck.

Most people won't do this because it's too hard, takes too long, and leaves no room for excuses.
IME, those that do do this get the process down 100% of the time.

Everything boils down to a set bevel.

Start there, if you can shave with the bevel, it's there or close.
Move to first Nagura - Botan usually. Hone till you think you are done.
Shave test the edge. did it improve the edge? Yes - proceed.
If the Botan edge did not improve the bevel, start over. Do not pass go, do not collect $200.
Handle the rest of the progression that way.
Eventually the finished edge shaves well, or you find out the technique, stone, or 1 or more Nagura are whack.
Stamps don't mean spit, btw - lotsa junk on the market these days, worse than ever before.

The full monty is on my website somewhere....

 

[alx gilmore]

I would just take edges that are ready for the final finishish to the hard jnat with tomo slurry. Matching tomos can be weird but just have to try them all. On my hardest stone I can use my hardest tomo but usually go with a very fine slightly softer tomo. I am using only weight of the blade at this point.

My go to progression for the dream edge is asano naguras on a hard full size jnat. This jnat though does not finish where I want so then I use tomo on my nicest jnat for the final finish. Usually that gets the edge where I want it, however an additional tomo session on the final stone has never hurt me.

While I don't use DMT slurry often, it can be used to compare 2 stones. Using a light DMT slurry to finish on 2 hard jnats will give a decent idea of how they finish cored to each other. While a smoother surface will make both of these edges better - diamond slurry let's you compare the stones with close to the same surface prep, and slurry from base stone only. Just know if any diamonds get in the slurry though you will have to set up the razor/stone again.

I know of no documentation that confirms that actual pieces of the loose diamond from a quality Atoma brand diamond lapping plate have chipped and or broken loose and were recovered to prove the shards were actually from the Atoma diamond plate. Do you have a link to any videos or photos of loose diamonds from an Atoma or a DMT plate or any other brand diamond plate, including that which might be termed Diamond Nagura?

There are many methods to hone a razor. But, if successful, they all end where the two bevels (A & B) meet. How they meet, maybe lopsided in width on side A or more so on side B, or one side is not fully developed and or the other side is over-developed. Ideally, Sides A and B should be of equal width, that is, from the cutting edge to the back where the factory hollow-ground demarcation line is. This bevel set procedure is not about the refinement/keenness of the edge but instead, it is only about the width of the bevels. The balanced width of A & B bevels acts as the framework platform which eventually will host the cutting edge be they sharp or not sharp.

The keenness, the true HHT 4+ or 5 or downright dull HHT 2, is what results when the sequence of the final progression of stones-sprays-powders or manmade or synthetic minerals or any other bound or loose abrasive form the apex as keen or not so keen.



The main reason that fellows are having trouble honing a razer is that they remove too much steel from one side.

If they over-honed Side A by 25% (25 strokes for the sake of argument) or so, then they will have to over-hone Side B by 75% to make them match symmetrically. This can be frustrating playing catch-up in the realm of micrometers. With the above scenario, you must then, with a microscope or good eye loop, count your next group of abrasive passes and begin to balance the two sides. You are playing catchup so it may take some time and effort. But once, and only then, by using a honing routine that works out to eventually represent an equal number of strokes on A & B will you find that you can create what is, and probably will be, the most demanding and fulfilling craft experience a guy will ever find. Not to mention the money saved by not having to buy expensive engineered but easy-to-dull commercial razor blades.

Once you have established a balanced edge-wise equal width of your bevels you can begin your abrasive sequence from coarse to medium to fine and super fine grits. This is most easily done and dependable when you count strokes by training yourself to balance your hand pressure. Heavy hand pressure has the same effect as adding more strokes. You don't want to go there, especially with rare, expensive tools, or oddly smithed razors or kamisori. This also holds for the stropping of leather. The abrasives in leather (silica) or those added Mohs 6-8 hard products (silica, included in linen along with juiced-up "super" products that are usually too coarse for shaving razors.

Ideally, if you schedule to always work in a sequence of ever finer and finer abrasives, the margin of error (as in all things natural) you will find that if you count strokes, and you keep notes as to what stones work with what razors you will if you are paying attention be spending less time on the stones and you shaves will feel professional.

Honing a knife or razor, a scalpel for an eye surgeon, since honing steel is the reduction of the thickness of the blade, it is wise to have a Step-by-step routine, and since stropping is also about reduction (we all know that horsehide contains silica don't we) careful stropping also benefits from a routine. I do not use pasted strops, they require care and feeding, like a small child. Co-mingling different abrasives kills a progression. I recommend that if you must use engineered powdered abrasives, have a separate strop for each one.

I do not know the math exactly, but I would guess that the difference to the average person in an attempt to judge if a razor was finished previously on:
500 grit. It is easy to see and deep scratches
1,000 grit. Harder to see and shallower scratches
2,000 grit. Not much harder to see, and not that much sharper
4,000 grit. Visually similar to 2k but much keener
8,000 grit. Visually as 4k but much keener
12,000 grit. Much much finer but not that much keener.

With this illustration, you can see that beyond 4,000 there is not enough difference or advancement benefit by going beyond 4.500 just as long as the edge geometry is perfect. The endgame difference in the quality of the shave as its longevity-endurance of a keener 6k, 10k, 15k, 30k edge might even diminish under the strains of cutting beard hair with these keener blades thereby leaving you with an unfinished or harsh shave..

I find that the silica dioxide and alumina oxide playground of "4k to 20k" grit is mostly a moot point when you or I, and we all do when we include A Stropping Regime.
Stropping is the leveling partner. If the bevels create a perfect V, stropping can make the V act finer. Easier to do at 4k, and more difficult at 1k, or 2k but beyond 4 or 4.5k the natural or most likely "packed" silica of choice by the strop maker within the obligatory leather strop will dominate and have the final say regarding the final state of keenness and comfort.

Stones form the platform so that stropping can be more efficient and precise.

Alx

 

[alx gilmore]

Could be, some shiro nagura are grit rich. I’ll try to post an image tomorrow.

Like up to 75% silica grit rich.
Alx

 

[Empire straights]

Like up to 75% silica grit rich.
Alx

I've never used Shiro but I like aggressive stones/slurry especially if it breaks down. I've been thinking about getting a mid range jnat but don't know what I should start with, I've only really ever had finishing stones and Mikawa nagura(and a few different finishing 'tomo nagura'. I have an Aiiwatani that's insanely soft and muddy, but very very fine. I don't even know if it breaks down, never tried, but it can take an edge from upper mid(4k-5) to finishing(10k+) in like 10 strokes. And I usually leave a milk thickness slurry because I don't want to cut my throat. I found it in a drawer and had never used it. It's been in there at least 2 years. I've only used it once, but was very impressed. It'll be gone quick if I start using it regularly. It seems special but I don't know enough about jnats to say so or not(maybe that's why they stupid expensive). I'll put it to work to dollar value isn' important. If like to get a brick of it to saw up. I think it was from JA.

 

[Christian1212]

I know of no documentation that confirms that actual pieces of the loose diamond from a quality Atoma brand diamond lapping plate have chipped and or broken loose and were recovered to prove the shards were actually from the Atoma diamond plate. Do you have a link to any videos or photos of loose diamonds from an Atoma or a DMT plate or any other brand diamond plate, including that which might be termed Diamond Nagura?

There are many methods to hone a razor. But, if successful, they all end where the two bevels (A & B) meet. How they meet, maybe lopsided in width on side A or more so on side B, or one side is not fully developed and or the other side is over-developed. Ideally, Sides A and B should be of equal width, that is, from the cutting edge to the back where the factory hollow-ground demarcation line is. This bevel set procedure is not about the refinement/keenness of the edge but instead, it is only about the width of the bevels. The balanced width of A & B bevels acts as the framework platform which eventually will host the cutting edge be they sharp or not sharp.

The keenness, the true HHT 4+ or 5 or downright dull HHT 2, is what results when the sequence of the final progression of stones-sprays-powders or manmade or synthetic minerals or any other bound or loose abrasive form the apex as keen or not so keen.



The main reason that fellows are having trouble honing a razer is that they remove too much steel from one side.

If they over-honed Side A by 25% (25 strokes for the sake of argument) or so, then they will have to over-hone Side B by 75% to make them match symmetrically. This can be frustrating playing catch-up in the realm of micrometers. With the above scenario, you must then, with a microscope or good eye loop, count your next group of abrasive passes and begin to balance the two sides. You are playing catchup so it may take some time and effort. But once, and only then, by using a honing routine that works out to eventually represent an equal number of strokes on A & B will you find that you can create what is, and probably will be, the most demanding and fulfilling craft experience a guy will ever find. Not to mention the money saved by not having to buy expensive engineered but easy-to-dull commercial razor blades.

Once you have established a balanced edge-wise equal width of your bevels you can begin your abrasive sequence from coarse to medium to fine and super fine grits. This is most easily done and dependable when you count strokes by training yourself to balance your hand pressure. Heavy hand pressure has the same effect as adding more strokes. You don't want to go there, especially with rare, expensive tools, or oddly smithed razors or kamisori. This also holds for the stropping of leather. The abrasives in leather (silica) or those added Mohs 6-8 hard products (silica, included in linen along with juiced-up "super" products that are usually too coarse for shaving razors.

Ideally, if you schedule to always work in a sequence of ever finer and finer abrasives, the margin of error (as in all things natural) you will find that if you count strokes, and you keep notes as to what stones work with what razors you will if you are paying attention be spending less time on the stones and you shaves will feel professional.

Honing a knife or razor, a scalpel for an eye surgeon, since honing steel is the reduction of the thickness of the blade, it is wise to have a Step-by-step routine, and since stropping is also about reduction (we all know that horsehide contains silica don't we) careful stropping also benefits from a routine. I do not use pasted strops, they require care and feeding, like a small child. Co-mingling different abrasives kills a progression. I recommend that if you must use engineered powdered abrasives, have a separate strop for each one.

I do not know the math exactly, but I would guess that the difference to the average person in an attempt to judge if a razor was finished previously on:
500 grit. It is easy to see and deep scratches
1,000 grit. Harder to see and shallower scratches
2,000 grit. Not much harder to see, and not that much sharper
4,000 grit. Visually similar to 2k but much keener
8,000 grit. Visually as 4k but much keener
12,000 grit. Much much finer but not that much keener.

With this illustration, you can see that beyond 4,000 there is not enough difference or advancement benefit by going beyond 4.500 just as long as the edge geometry is perfect. The endgame difference in the quality of the shave as its longevity-endurance of a keener 6k, 10k, 15k, 30k edge might even diminish under the strains of cutting beard hair with these keener blades thereby leaving you with an unfinished or harsh shave..

I find that the silica dioxide and alumina oxide playground of "4k to 20k" grit is mostly a moot point when you or I, and we all do when we include A Stropping Regime.
Stropping is the leveling partner. If the bevels create a perfect V, stropping can make the V act finer. Easier to do at 4k, and more difficult at 1k, or 2k but beyond 4 or 4.5k the natural or most likely "packed" silica of choice by the strop maker within the obligatory leather strop will dominate and have the final say regarding the final state of keenness and comfort.

Stones form the platform so that stropping can be more efficient and precise.

Alx

I only use my diamond plate to lap my stones and I have noticed that they become slower over time. From what I have read the diamond plates don't last forever because the substrate holding the diamonds weaken and the diamonds become loose but maybe they just slowly wear down? My comment was based off personal experience and some assumptions though so I could be wrong. I would be interested if you had any documentation on how/why a diamond plate wears over time and how that could affect slurry production.

From personal experience I always get better results from a good tomo nagura vs diamond plate (even a well worn dmt 325). I have had in the past slurry built from a diamond plate contain some sort of large particle that did bring the edge back. It is not a common occurrence but I have noticed it a couple times when I used diamond slurry. That is one of the reasons why I recommend a tomo over diamond plate. Diamond plate for slurry definitely has it pros, but my preference still falls with tomo naguras.

I agree there are many ways to get a razor sharp. I think if someone is able to get a good shaving edge and trying to test a stone for its finishing abilities - the best method for me, has usually been take an edge you know is ready for final finishing to that stone.