# Agate sharpening stone



## GorillaGrunt (Mar 23, 2021)

after posting the non-japanese natural stone thread I’ve been going haam buying these and some jnats too. This is the green marbled one, sold as agate and also as jade I believe, all over Amazon and Alibaba and sites like that, shipped from China I think. It’s listed as 10k, which I dismissed on account of its being a natural stone and not sieved grit, and also on account of its being a $11 Internet stone. I put a little ikasaki on it, worked the bevel a bit, then the edge. I looked at the scratch pattern, noticed a lack of contrast which again I didn’t expect to get since this is not a Jnat or kasumi-friendly-designed synth, felt the edge which was rather slick, and thought to myself well it’s no 10k but it’s 10 bucks so we’ll see.

Then I cut into a paper towel.

What I thought was the scratch pattern from this stone was the scratch pattern from whatever stone I had done those bevels on previously, brought out because this stone mirror polishes faster than anything I’ve ever seen. And what I thought was an edge that either hadn’t reached the apex or rolled over it was in fact sharp like a razor and completely burr free, swiping through the towels in a way I don’t usually see.

I then tried natural nagura slurry, which gave a little contrast and a toothier edge, then washed it and raised slurry with a diamond plate, which gave a different sort of contrast and a slightly toothier edge than plain but not as much so as with nagura. I suspect it works like a coticule in that slurry makes it coarser instead of finer, and clean with plain water is the finest mode.

I’m not saying it’s a great or magical stone, but it does a few interesting things that I haven’t gotten other stones to do, and it kind of does what I wanted the 12k Naniwa to do so I’m posting that up for sale. Potential minuses: no contrast at all, no toothiness, reveals any scratches on bevels, very slick with no slurry to the point where it’s hard to find the angle. Pluses: cuts and polishes very fast, apparently goes right to the apex like a razor edge without leaving any burr - like literally not any different without stropping versus with. I’m figuring I can get some cool results messing around with various nagura and slurry levels but it’ll likely take some practice.









Top is Murata Blue 1 165mm koyanagi, diamond plate slurry on agate. Bottom is Tosa 135 (?) ikasaki, maybe white steel? Clear water on agate, the reflectivity makes me think that the visible scratches are from previous stone finishes. I’ve just messed around with all kinds of stones on these knives and did not start with any sort of controlled finish on either.

And if anyone knows more about this, the geological or metallurgical mechanisms at play, I’d love to know.


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## DavidPF (Mar 23, 2021)

I only learned this just now by looking it up, but geologically there are two types of jade, and neither one of them has much to do with agate. Agate is a type of quartz; the two types of jade are jadeite (which is the "good stuff" from a jewellery point of view) and nephrite.

Agate is the least dense of the three, with a specific gravity around 2.6

Nephrite's specific gravity is just shy of 3

Jadeite's is about 3.4

(So you'll know which one it is by taking its weight in grams divided by its displacement in millilitres.)


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## Walla (Mar 23, 2021)

Very interesting...I had always written them off as being crap..looks like I might drop the +-10 bucks.

Thanks for your insight.

Take care

Jeff


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## GorillaGrunt (Mar 23, 2021)

DavidPF said:


> I only learned this just now by looking it up, but geologically there are two types of jade, and neither one of them has much to do with agate. Agate is a type of quartz; the two types of jade are jadeite (which is the "good stuff" from a jewellery point of view) and nephrite.
> 
> Agate is the least dense of the three, with a specific gravity around 2.6
> 
> ...



I’m assuming it’s either something to do with translation or something to do with SEO-type keyword loading. looks like probably agate. Also quartz content makes sense as a sharpening rock.

ive got another on the way that is allegedly granite, which ive never heard of as a sharpening stone, but also contains quartz.


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## DavidPF (Mar 23, 2021)

GorillaGrunt said:


> Also quartz content makes sense as a sharpening rock.


Makes sense.

The part of granite that isn't quartz is often mostly feldspar, a major component in ceramics and nearly as hard as quartz, so I guess it's not so weird.


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## GorillaGrunt (Mar 25, 2021)

Got the granite; it looks like it’s literally a scrap from a countertop so I probably overpaid, but it wasn’t too much. Initial impressions are — not exactly like the agate but closer to that than to a sedimentary stone. I’ll have to try on some different steels and with some nagura to get a sense of the range of this thing, but the one thing I noticed right away was that there’s a rougher side and a polished side, and surprisingly the polished side is the more aggressively cutting one. Edge feels kind of like off the agate but maybe more a slicing than pushing edge, if that makes sense.


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## DavidPF (Mar 25, 2021)

Total speculation on my part, but maybe on the diamond-sawed polished side the individual crystals that have been sawn in half have fresh sharp edges.


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## GorillaGrunt (Mar 26, 2021)

Maybe - we'll see what happens when i lap both sides with the diamond plate or stone fixer


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## jwthaparc (Mar 26, 2021)

Wow I totally wrote those agate stones off as complete crap, when I saw them for sale. Maybe one day when I have an extra ten bucks laying around I'll grab one.


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## GorillaGrunt (Mar 26, 2021)

I wrote off pretty much everything that wasn't a jnat - then i decided to buy a couple more jnats and just ran into so much more potentially interesting stuff that wasn't too expensive


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## jwthaparc (Mar 26, 2021)

Jnats are great, but unless you are buying koppas, they are way too expensive (for the most part) I have 4 and 3 of them are koppas. I need to start trying other naturals when I get a chance.


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## GorillaGrunt (Mar 26, 2021)

Jnats are great for polishing bevels, and I really do like the edges. But if you're not polishing for contrast there are more options out there besides jnats and jsynths. Haven't tried any of these new stones on higher alloy steels though


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## jwthaparc (Mar 26, 2021)

GorillaGrunt said:


> Jnats are great for polishing bevels, and I really do like the edges. But if you're not polishing for contrast there are more options out there besides jnats and jsynths. Haven't tried any of these new stones on higher alloy steels though


Like what? I have a venev diamond bonded stone, also a Bryxco manticore on the way. Is that what you are talking about? As far a new stones for wear resistant steel.


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## GorillaGrunt (Mar 26, 2021)

Oh I mean there are lots of natural options out there outside of Japan, the various natural razor hones and so on plus the quartz based ones and gathered slates, but I don’t know if some of them are only suitable for the simpler carbon steel.


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## jwthaparc (Mar 26, 2021)

GorillaGrunt said:


> Oh I mean there are lots of natural options out there outside of Japan, the various natural razor hones and so on plus the quartz based ones and gathered slates, but I don’t know if some of them are only suitable for the simpler carbon steel.


Oooh. Gotcha. 

I think the quartz ones might be able to handle higher end steels actually. From what I've heard. I believe Arkansas stones are quartz based, and I've heard of people using them on high vanadium content steels. Though they may be slower than stones like my venev diamond.


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## KingShapton (Mar 26, 2021)

jwthaparc said:


> Though they may be slower than stones like my venev diamond.


So did your Venev stone arrive? What is the first impression like?


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## MarcelNL (Mar 26, 2021)

many years ago my dad was using Arkansas stone to sharpen chisels, I just remember a seemingly endless process with what I now think was caused by him jumping from rather course to way too fine. I have also recently seen 'natural Ruby' and Agate stones ; Natuurlijke polijststeen voor Higonokami #3000/#10000 and always wondered how that would feel with a knife.


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## jwthaparc (Mar 26, 2021)

MarcelNL said:


> many years ago my dad was using Arkansas stone to sharpen chisels, I just remember a seemingly endless process with what I now think was caused by him jumping from rather course to way too fine. I have also recently seen 'natural Ruby' and Agate stones ; Natuurlijke polijststeen voor Higonokami #3000/#10000 and always wondered how that would feel with a knife.


Ruby is basically aluminum oxide.


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## GorillaGrunt (Mar 26, 2021)

Yeah i know quartz is "harder than steel" but i don't know if that applies to the kinds of steels we use here, or the more abrasion resistant ones. I do know that the only ones I've tried that simply wouldn't sharpen on a jnat - the steel abrades the stone instead of the other way round - were ZDP and HAP. I'm pretty sure I saw some benefit from finishing SLD on naturals but i haven't had any SLD in a while and i keep getting better at sharpening and realizing that just a little while ago i wasn't that good at it.


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## Bolek (Mar 26, 2021)

jwthaparc said:


> Ruby is basically aluminum oxide.


Ruby contain also Cr. Al2O3 is sapphire


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## MarcelNL (Mar 26, 2021)

In the end all stones are chemistry, the difference is how it's presented and what it does to which steel.


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## jwthaparc (Mar 26, 2021)

GorillaGrunt said:


> Yeah i know quartz is "harder than steel" but i don't know if that applies to the kinds of steels we use here, or the more abrasion resistant ones. I do know that the only ones I've tried that simply wouldn't sharpen on a jnat - the steel abrades the stone instead of the other way round - were ZDP and HAP. I'm pretty sure I saw some benefit from finishing SLD on naturals but i haven't had any SLD in a while and i keep getting better at sharpening and realizing that just a little while ago i wasn't that good at it.


Yeah I was saying that you can use them on high vanadium content steels from what I've heard. Though I havent tried this myself


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## jwthaparc (Mar 26, 2021)

Bolek said:


> Ruby contain also Cr. Al2O3 is sapphire


Yeah so basically aluminum oxide.


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## GorillaGrunt (Mar 27, 2021)

The granite is much much grabbier than the agate, not slick like that at all. Very easy to find the angle. Especially on the polished side for some reason, maybe as DavidPF says or something like that.


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## Tzasabi (Mar 27, 2021)

Greek Oil stones may be of use , natural stones from the mountains on Crete.
Help give a pretty good edge.


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## GorillaGrunt (Mar 27, 2021)

Is that the one called Levant hone?


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## Tzasabi (Mar 27, 2021)

GorillaGrunt said:


> Is that the one called Levant hone?


Yes, ladakono in Greece ...


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## cotedupy (Mar 29, 2021)

Some thoughts... 

I'm going to go against the grain (ho ho) and say I think it's more likely to be Nephrite Jade than Agate. For a start - it looks quite a lot like a nephrite jade stone, or at least the pictures of them I've seen, and they'd be a lot more common than agate stones I think. Secondly - fine stones based on quartz (of which there are many), are probably going to rely on at least some release of particles in mud, as quartz particles I think tend to be comparatively rounded. If your stone was agate, I don't really see it doing much quickly, even at a super fine level.

I might be completely wrong; it's just impressions I have from what I've read.

There's some stuff in here about Jade, particularly page 18: https://bosq.home.xs4all.nl/info 20m/grinding_and_honing_part_2.pdf

I'd be interested to hear how you get on with the granite. How fine is it? Can you see the quartz in it? I would have thought a granite stone is going to be better for grinding, or sharpening something like an axe, because of how hard it (or the bond) is. Or flattening. As a stone for kitchen knives, I'd imagine the differing hardness/density of quartz, mica, and feldspar might give you quite an uneven finish, especially if the grain size is larger.

Again that's speculation from things I've read... I've not tried any of these, so very keen to hear your and others thoughts.


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## GorillaGrunt (Mar 29, 2021)

Who knows, I looked at a bunch of pictures of stones online and guessed - so it could be nephrite or something else. I’m surprised that both that one and the granite sharpen at all, but I’m not a geologist, just a guy who’s only sharpened on sedimentary rocks and their synthetic analogues until now.

The granite isn’t a particularly fast stone I don’t think and I think none of these are good for bevel polishing or heavy grinding. I tried it on a bevel to see what happens and it’s nothing like the agate, not terrible but it doesn’t seem very even as you said. I’m thinking these are mostly good for edges as a finishing or prefinishing stone. Received wisdom at least is that you get a toothier, longer lasting edge from natural stones because of the varying particle size so that makes sense.


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## HumbleHomeCook (Mar 29, 2021)

jwthaparc said:


> Yeah I was saying that you can use them on high vanadium content steels from what I've heard. Though I havent tried this myself



I have a forty odd year love affair with Arkansas stones. Do NOT use them on high vanadium steels. There was a time when I thought you could and publicly declared such. I was wrong. The novaculite (quartz) is much softer then the vanadium carbides and all you're really going to accomplish is abrading the matrix and burnishing the carbides. Eventually, you'll glaze your stones over. If someone wants to lap a black or translucent for polishing, so be it but my Arkansas stones will not again see high vanadium carbide (4%+) or really any high hardness steels in my lifetime.

What's more, the high vanadium carbide steels are better served with diamonds.


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## DavidPF (Mar 29, 2021)

Bolek said:


> Ruby contain also Cr. Al2O3 is sapphire


Ruby = sapphire

Sapphire = ruby

Only in jewellery does the difference matter.


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## jwthaparc (Mar 29, 2021)

HumbleHomeCook said:


> I have a forty odd year love affair with Arkansas stones. Do NOT use them on high vanadium steels. There was a time when I thought you could and publicly declared such. I was wrong. The novaculite (quartz) is much softer then the vanadium carbides and all you're really going to accomplish is abrading the matrix and burnishing the carbides. Eventually, you'll glaze your stones over. If someone wants to lap a black or translucent for polishing, so be it but my Arkansas stones will not again see high vanadium carbide (4%+) or really any high hardness steels in my lifetime.
> 
> What's more, the high vanadium carbide steels are better served with diamonds.


Good to know. I was going off of what I heard a youtube sharpener say. I shouldn't have even believed him. 

I think in the same video he goes on about how Arkansas stone are the best out there and that he tried using his friends (super expensive he said) jnat, and it didn't get the knife sharp, so jnats suck (I should have completely wrote off everything he said after that).


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## captaincaed (Mar 30, 2021)

HumbleHomeCook said:


> I have a forty odd year love affair with Arkansas stones. Do NOT use them on high vanadium steels. There was a time when I thought you could and publicly declared such. I was wrong. The novaculite (quartz) is much softer then the vanadium carbides and all you're really going to accomplish is abrading the matrix and burnishing the carbides. Eventually, you'll glaze your stones over. If someone wants to lap a black or translucent for polishing, so be it but my Arkansas stones will not again see high vanadium carbide (4%+) or really any high hardness steels in my lifetime.
> 
> What's more, the high vanadium carbide steels are better served with diamonds.


I lapped a translucent ark. RIP diamond plate. 
The slurry cuts super fast though. Try it for a party trick sometime. The slurry goes dark grey in about a minute, and it chews up steel.


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