Effective "grit size" of natural stones

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Honestly I like keeping it a bit mysterious. Natural stones are a finite resource. I like seeing people who actively pursue nuanced knowledge about them being the ones who buy them. I wonder if reducing them to grit numbers encourages reductionist pursuits. Maybe it just helps overall education. Maybe I’m a little elitist. Maybe I should take my nonsense to Unpopular Opinions.
 
Honestly I like keeping it a bit mysterious. Natural stones are a finite resource. I like seeing people who actively pursue nuanced knowledge about them being the ones who buy them. I wonder if reducing them to grit numbers encourages reductionist pursuits. Maybe it just helps overall education. Maybe I’m a little elitist. Maybe I should take my nonsense to Unpopular Opinions.
Numbers on naturals used to trigger me too. I guess I'm mellowing with age. If it helps someone I'm good with it, even if it is just a generalization.

I won't be putting you on ignore anytime soon for your "unpopular opinion".
 
Honestly I like keeping it a bit mysterious. Natural stones are a finite resource. I like seeing people who actively pursue nuanced knowledge about them being the ones who buy them. I wonder if reducing them to grit numbers encourages reductionist pursuits. Maybe it just helps overall education. Maybe I’m a little elitist. Maybe I should take my nonsense to Unpopular Opinions.
This makes a further case for leaving out rare stones.

Incidentally I would appreciate a reply to the private message I sent, even a simple "no thanks."
 
This is grossly oversimplified.
But here is the Arkansas family, according to me.

Washita 500-8000
Soft Arkansas 600-1200
Medium Arkansas 1200-2000
Hard Arkansas 2000-4000
Translucent Arkansas 4000-6000
Surgical Black Arkansas 6000-8000

I found some earlier estimates you gave in another thread, copied below. It raises a few questions:
  • Would you say a typical good Washita works 500 to 2000, and the finer action is less common or harder to get?
  • "A hard ark is basically an 8k stone" yet I see you now rate the Translucent as 4000-6000—a change in view or a different expression of it?
  • You rate the Belgian Blue coarser than most other references. Do you think this is variability in stone, different application, or simply incorrect?
A good coticule can cover a range from 1500-8k synthetic. I consider them to be the be all and end all for mid range razor work. A bbw might be 2k-4k, slower and not capable of finishing as fine. I wouldn't use one for razors but they are great for finishing knives.

I wouldn't normally use soft arks or washitas for razors. But I do use them for knives and tools a lot. A washita (in my mind) should be able to do work from about 500-2k. Whereas a soft ark is basically like a slow 1000 grit stone. And that's it. Kind of boring by itself but I like them for touching up apexes. I have about a dozen little soft Ark pocket stones stashed all over my house kitchen, work kitchen, basement, toolboxes, etc. A hard ark is basically an 8k stone (unless you lap it very coarse and then it can cut like anything down to a 500 grit diamond plate for a little bit).
 
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I think a list of the relative grit range of different natural stones is a great idea! Putting a grit rating can be tricky, though.

Would be nice to at least have an equivalency of naturals with synthetics, though.
 
[*]Would you say a typical good Washita works 500 to 2000, and the finer action is less common or harder to get?

Yes. There are harder and finer versions of washitas out there. They are mostly very very old (mined 120+ years ago). They don't have labels or boxes and you won't know if you have one until you have tried and struck out a bunch of times. The common labelled modern washitas (1930s on) are much more standardized in their composition and performance as coarse to mid-grit stones.


[*]"A hard ark is basically an 8k stone" yet I see you now rate the Translucent as 4000-6000—a change in view or a different expression of it?


I think that you can surface treat a translucent so it performs very close to a black (8000kish). But by it's nature it is slightly more coarse. I have an 8*2 Dan's surgical Black which is pretty much the top of the line in my opinion. It might even be 10-12k in a more patient person's hands as @captaincaed mentioned above. Fantastic razor finisher. So for me, I find the translucents more useful with a coarser surface treatment. This will actually make it work quite fast maybe even down to 1-2k speed. But the burst of speed will be short lived and settle down around 4-6k.


[*]You rate the Belgian Blue coarser than most I other references. Do you think this is variability in stone, different application, or simply incorrect?


I have never been a fan of Belgian blues. I have had ten or twelve. But I have only had ones attached to rather magnificent coticules. The blue side always seemed both coarser and slower than the yellow side. That's a pretty terrible combination of attributes so to be perfectly honest I have barely used them. I'm probably not the best judge.
 
Here's where a natural Belgian combo is such a great trick. The yellow layer will usually cut fast regardless of grit(and has great tactile feedback, and helps keep the burr small and in check). Because the range of potential grit of the yellow is so vast, sometimes you get lucky. This is an "island of disappointment" yellow layer. But the BBW layer is usually more consistent rock to rock. After refining the edge, I can knock it back down to "useful in food" grit with the blue side.

 
As it relates to objective particle size, I do think that it's a pretty useless measure of how natural stones work. Pretty much every stone from the Kyoto area (which includes 90% of the Jnats people think about) have the same particle size. Same goes for cuticles, novaculite, etc. And yet there is HUGE variation in the sharpening behavior of these stones. So in terms of scientific, get out the microscope and measure particles... yeah, I think its not a good idea and perhaps misleading in terms of performance.

I 100% see the motivation. As I said, I don't like assigning numbers to JNats, but it is also the thing I get asked about the most and unless you have a deep experience with these stones to draw on, it can be hard to compare. Having some frame of reference for what to expect is valuable.

While there are all sorts of caveats, there is value in having ballpark numbers, however rough. Knowing directionally what to expect from a high hardness eastern mine suita vs a soft western mine suita is helpful.

But the polishing bit complicates things too, which is more than half the point with Jnats in particular. So not sure how to get that info into a chart either...


Have you managed to come across any PSA numbers for JNATs? just for interest
 
Here is a first draft of what I am thinking. How does this design look?

Naturals draft1.png
 
https://loosbrynet.se/en/ reads "Loosbrynet (meaning Loos Whetstone) is a fine-grained Swedish waterstone, quarried locally in the northernmost part of Hälsingland; it is cut from slate formed on the ocean floor, with a grit varying around 1200-1500."

Are these JIS or perhaps FEPA equivalent values? @RDalman
 
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I take from the "Likes" on #39 that my format is approved. I turn my attention to selection. I combined Hard Translucent and Surgical Black into a single item as I believe these are too similar to chart separately, with natural variation being larger than any difference between them. If you feel this is wrong please say.

This is my current selection. What do you think of it?
  • Amakusa
  • Aoto (combined soft & hard)
  • Belgian Blue
  • Coticule
  • Cretan Oilstone
  • Dalmore Blue
  • Gotlandsbryne
  • Hard Arkansas
  • Hard Translucent and Surgical Black Arkansas
  • La Lune
  • Omura
  • Orsa Bryne
  • Pierres Levant (same as Aiguiser Naturelle de Saurat?)
  • Rouge du Salm
  • Rozsutec
  • Sasaguchi
  • Soft Arkansas
  • Tam o' Shanter
  • Thüringian
  • Washita
  • Water of Ayr
 
https://loosbrynet.se/en/ reads "Loosbrynet (meaning Loos Whetstone) is a fine-grained Swedish waterstone, quarried locally in the northernmost part of Hälsingland; it is cut from slate formed on the ocean floor, with a grit varying around 1200-1500."

Are these JIS or perhaps FEPA equivalent values? @RDalman
I'd guess FEPA. I don’t know, am not affiliated with them, but ime the loos hone finishes somewhat 1500-2000. Similar to your belgian blue in action but maybe ~half in grit.
 
I don't think I have room for both the Saurat 'Genre Levant' and the Loos stone. Which one should I pick, or neither? @cotedupy I know you have the Saurat; do you also have the Loos?
 
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I don't think I have room for both the Saurat 'Genre Levant' and the Loos stone. Which one should I pick, or neither? @cotedupy I know you have the Saurat; do you also have the Loos?

I'm afraid it's one of the very few types of (documented) western whetstone that I don't have and have never used. I don't see any problem with taking the info from G&H though if you want to include it.

NB - the name 'Pierre de Levant' shouldn't be used in a chart like this, as it can be confusing. I know of at least three completely different types of whetstone (from three different countries) that have all historically been called PdL or 'Stone of the East'.

---

Here's a go at some of your list above, I've left off the Japanese ones because even when I have used them - other people will have more knowledge. And also a couple of Swedish sounding things that I'd never even heard of! And added in some other very common types of historic whetstones at the bottom.


  • Belgian Blue 3-5k*
  • Coticule 600 - 14k**
  • Cretan / Turkish Oilstone 2 - 10k
  • Dalmore Blue 3 - 5k
  • Hard Arkansas 6 - 8k***
  • Hard Translucent and Surgical Black Arkansas 15k+***
  • La Lune 10k
  • Pierre de Saurat / Pyrenees Stone 2 - 6k
  • Rouge du Salm 3 - 5k*
  • Rozsutec 6k
  • Soft Arkansas 800 - 2k
  • Tam o' Shanter 6k - 10k
  • Thüringian 15k
  • Washita 600 - 6k
  • Water of Ayr 10k - 14k
  • Charnley Forest 8k - 12k ***
  • Llyn Idwal 6k - 12k ***
  • Welsh Slates (Yellow Lake Oilstone, Glanrafon, Nantlle Valley &c.) 6k - 14k
  • Hindustan 3 - 5k


* I wouldn't include both BBW and RdS (or indeed La Lorraine). It's a matter of some confusion as to what might be what, and what's been called different things in different mines at different times. They all act similarly enough.

** You don't get all of this range in a single stone. More friable cotis can have a significant range, but it's never this large.

*** Arkansas and other hard novaculites are extremely difficult to rate in this way. If you raise an atoma slurry on a translucent ark / Charn / Idwal it will abrade like a 1k synth. If you use a burnished surface they'll finish as high as any natural whetstone, and in the case of trans and black arks - higher than anything else.


---

Coupla other things to note...

While I have a good amount of experience with the stones above (most of which I've had dozens of example of), I'm certainly not claiming my analysis of their 'grit rating' is any more valid than anyone else's. People interpret different stones in different ways, and use them in different ways.

For instance my ratings above refer to what I think about edge finish levels, and a lot of them for razor finishing, which happens with next to no pressure. And very few of those stones would ever get used for polishing in the way that Japanese stones do. On the other hand Ed T has given more bias toward the polishing level of the Jnats he rated, and that's going to come out slightly lower than an edge finish rating. There are jnats that will happily finish the edge of a razor at the 15k level I've put Thuringians at.

The reason for that difference is complicated, but I'd just emphasize again what I said previously on this thread: Hardness or friability of natural stones is an overwhelmingly important factor, both in terms of polishing and edge finish. It's considerably more significant than particle size.
 
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I have a thuringian (thanks oli) and a Dan's surgical black. The finest stone I have is way beyond them. It is the hardest glassiest stone I have encountered. Let's call it 20k. It was sold to me as jasper. I have only had one other piece similar and it was totally different colors and not quite as hard or fine. This one is nuts. Makes the razor too sharp for several shave until it mellows a bit. Whoever originally lapped it put hundreds of little scratches in it. Without those little scratches everywhere I don't think it would cut at all. Just burnish. But after a few strokes of a razor you see slurry. You can use water or oil or even dry. It's really remarkable. But doesn't work great for the chart because I've been looking for another one for the past 4 years.
PXL_20240303_134803180.jpg

PXL_20240303_134813107.jpg
 
I want to second what cotedupy is saying about stone range, from my more limited experience.
  • Hardness is often more important than abrasive particle size since the line between abrasive and binder is fuzzier in natural stones vs synths. If you have a solid mass of abrasive and the particles are large-ish, let's say 5-10um, the close packing and non-friability means you'll have a flat honing surface that finishes in the 0.1-1.0um "effective grit" range since you're only using the very tip of each abrasive iceberg. If you slurry a stone line this it'll cut more like its particle size implies, e.g. translucent Arkansas
  • Many top end stone ranges are when honing razors with fixed angles and light pressure. For knives I find the effective top end of the range much lower unless you're being incredibly careful/fussy.
 
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And also a couple of Swedish sounding things that I'd never even heard of!
Info 20M G&H3 page 107 and following?

* I wouldn't include both BBW and RdS (or indeed La Lorraine). It's a matter of some confusion as to what might be what, and what's been called different things in different mines at different times. They all act similarly enough.
This is a surprise. Henk Bos, Info 20M G&H4 page 48:
  • Wine Red colour.
  • Grit 4000 - 8000 depending on thickness of the slurry and the applied pressure.
  • The "Rouge du Salm" sharpens considerably better than the "Belgian Blue" whetstone.
  • It is possible to bring a knife up to shaving performance. Including the HHT!
Is not the wine red color a useful identifier? You disagree on the finer performance and "considerably better" sharpening? His series is by far the most extensive I have found, and includes six samples of this stone, so I am reluctant to disregard it.

** You don't get all of this range in a single stone. More friable cotis can have a significant range, but it's never this large.
Very useful information which I will try to represent reasonably. What would you say is a normal range for a good representative Coticule sample?

*** Arkansas stones and other hard novaculites are extremely difficult to rate in this way. If you raise an atoma slurry on a translucent ark / Charn / Idwal it will abrade like a 1k synth. If you use a burnished surface they'll finish as high as any natural whetstone, and in the case of trans and black arks - higher than anything else.
I want to include the Arkansas stones due to their ubiquity, but I understand that this received-finish behavior makes any assigned value less useful and more contentious. (At least in the case of sintered ceramic there exists a factory finish that is a reasonable reference point.) I will leave out the Charnley Forest and Llyn Idwal stones unless you suggest otherwise.

There are jnats that will happily finish the edge of a razor at the 15k level I've put Thuringians at.
Are there any fine Japanese naturals that you would suggest including? It seems that this area is highly specialized and highly variable, and outside the scope of my chart.

The reason for that difference is complicated, but I'd just emphasize again what I said previously on this thread: Hardness or friability of natural stones is an overwhelmingly important factor, both in terms of polishing and edge finish. It's considerably more significant than particle size.
I understand that individual samples will have different hardness levels, but would it be useful to include a color coding for the general nature of soft, medium, or hard for each type? This may be too much and too confusing within the GLGC but I could at least try it out. I may try to create a separate natural whetstone chart with an additional axis and room for more information.

Thank you for the detailed reply!
 
I want to second what cotedupy is saying about stone range, from my more limited experience.
  • Hardness is often more important than abrasive particle size since the line between abrasive and binder is fuzzier in natural stones vs synths. If you have a solid mass of abrasive and the particles are large-ish, let's say 5-10um, the close packing and non-friability means you'll have a flat honing surface that finishes in the 0.1-1.0um "effective grit" range since you're only using the very tip of each abrasive iceberg. If you slurry a stone line this it'll cut more like it's particle size implies, e.g. translucent Arkansas
  • Many top end of many stone ranges are when honing razors with fixed angles and light pressure. For knives I find the effective top end of the range much lower unless you're being incredibly careful/fussy.
A pithy summary. Do you mind if I borrow this for my README?
 
I have a thuringian (thanks oli) and a Dan's surgical black. The finest stone I have is way beyond them. It is the hardest glassiest stone I have encountered.
Have you by chance used a polished sintered ceramic, like a resurfaced Spyderco Fine or Ultrafine, or resurfaced Norton Ascent?
 
  • Cretan / Turkish Oilstone 2 - 10k
In this video you gave a range of "800 and 8000" and earlier, quoted below, you gave 500 to 7000 and described it as faster than a Washita. Why the change?

The Turkish Oilstone is a remarkable stone. In terms of speed it is completely unequalled by anything, natural or synthetic, that I've tried.

The stone is comparable to a Washita in that it can be used with varying pressure to give an effective 'grit' level going from around 500 up to about 7k. But it's faster than a Washita, and doesn't clog as much, both of which I assume are down to how friable the stone is - grit is released and new surface is being exposed constantly when worked heavily.
 
Have you by chance used a polished sintered ceramic, like a resurfaced Spyderco Fine or Ultrafine, or resurfaced Norton Ascent?
I have tried the UF and also resurfaced a Fine. I haven't used them enough to have a strong opinion yet but I can if it would be helpful. My knee jerk respond is "around a Trans Ark but not quite there".
 
I have tried the UF and also resurfaced a Fine. I haven't used them enough to have a strong opinion yet but I can if it would be helpful. My knee jerk respond is "around a Trans Ark but not quite there".
I currently have the Spyderco sintered ceramics charted based on estimates of the performance of their factory finishes. If there is a consensus on how finely a resurfaced one performs on the razor forums—or you become confident in asserting one yourself—I may add it to the "Other" column.
 

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