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

Maxim wrote:

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 !

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.

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

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.

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.

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

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.