A sharpening thread of my very own (Japanese Natural Stones).

[Pat Barry]

Mike, allow me to insert some additional opinions.

Two points I would like to remind you of before I share my opinions:
1. Remember, what really determines the sharpness of a blade at the microscopic level where the cutting of wood gets done are the last few strokes on the last stone in the process. Everything before that is prep.
2. It is very difficult to objectively measure sharpness, and objectively measuring how long a blade remains "sharp" (whatever "sharp" means) is even more difficult. Anyone who tells you otherwise is blowing smoke up your skirt.

Let's compare synthetic and manmade stones a bit, sans the romance and history and Japanese words.

Modern manmade stones cut HC steel very, very well. This capability is extremely useful for wasting metal. Why do I believe that synthetic stones cut steel so effectively, and why are they more effective than natural stones, you may ask? The chemical particles used to make synthetic stones are measurably harder than the stone particles that comprise natural stones, so they cut steel more efficiently. In addition to being harder, the individual particles in synthetic stones have distinct, sharp corners, whereas the particles in natural stones (at least the Japanese version) tend to be rounder. Hard and angular versus soft and round. Oops, starting to sound a like a romance novel, perhaps "Love's Savage Secret?"

That reminds me of an old Japanese saying that goes something like this (not intended to be erotic): "A wife should be a stone to polish the blade that is her husband." Sharpening stones have a place deep in Japanese culture.

Anyway, back to the subject at hand.

While is is difficult to quantify the results, the process of sharpening a blade is straightforward. When you finish (vs "shape" or "prep") a blade on a any stone, whether synthetic or natural, the stone's particles plow a parallel row of furrows in the surface of the blade. The extreme leading edge of the finished blade viewed under a microscope looks quite jagged. The sharper a blade is, the thinner and more uniform this jagged edge will be. How long it will stay sharp is driven by how long it takes for the carbides exposed at this thin jagged edge to be torn off, and for the edge to round over. The sharpening stone can increase the amount of wood a blade can cut before dulling by creating furrows that tend to support the carbide particles and protect them from being torn off.

According to Ron Hock, and consistent with other studies I have seen, synthetic stone particles, being sharp and jagged, tend to plow furrows that are deep and V-shaped with walls sloped at relatively uniform angles, and narrow bottoms. The angled sides of these parallel furrows reflect light in a uniform manner, which explains perfectly why blades worked on synthetic stones easily achieve a mirror finish. By comparison, the rounder particles of natural stones cut shallower furrows with curved sides, and of course, rounded bottoms, diffusing reflected light, and producing a cloudy, misty appearance (at least ideally).

Appearance aside, I believe a high-quality high-carbon steel blade containing fine, evenly-distributed carbides as found in most hand-forged blades made of high-purity steel, and finished on a natural stone will stay sharper longer than the same blade finished on a synthetic stone of the same grit size. I have no hard data to support this opinion. But I believe the shallower, rounder furrows (or scratches) created by natural stones tend to support and hold in place the carbide crystals longer. This seems consistent with the SEM photographs I have seen, and feels consistent with how my blades perform when cutting wood.

I have been using natural Japanese finishing stones for a long time, but I don't care what mountain, or mine they came from, or what goofy name they have stamped on them. All I care about is how they perform during those last few strokes. I know the job is complete when the blade is free of visible scratches and the HC steel edge is a beautiful misty white color, and the low-carbon supporting steel is a matt grey. I don't have to test such a blade for sharpness, because I can sense it is very sharp. This is a very satisfying feeling, and one that is difficult (but not impossible) to obtain with a synthetic stone.

My advice is don't venture too close to the edge of this rabbit hole until you are truly ready to jump.

Stan

Very interesting theory Stan. I think you have done a good job of explaining the process and result. I do find your conclusion about round particles leading to the misty white color and grey matte finish or not because my initial thought would be that sharper points would lead to finer scratches and thus the milky appearance - who knows without a SEM study? I have a question though and it ties in with Brian's initial postings and or video and your description. Do you tend to use the final stone with a slurry built up on it or just clean with water. I recall Brian mentioning that he develop a slurry although I don't recall if this was for the coarse work or the final steps.

[ken hatch]

Ken,

Interesting, they must have a big range in hardness. It seems the Yaginoshima Asagi are the same way, people use them for razors and for knives, which as you know are totally different, so my assumption is that there is a pretty wide range of hardness for some mines. The stone I have is fairly hard for how fast it cuts.

Sounds like you have one on the harder side, which is great. Is it easier to use than the Nakayama?

Brian,

I can't answer ease of use for the Nakayama just yet. It is too new and I'm still getting use to it but I just sharpened one of my #2 White Steel push chisels using the Kiita and finishing on the Nakayama. The Kiita finish was more than adequate with no lined up scratches to the edge, the chisel was good for anything you could ask of it. The follow up with the Nakayama just refined the matt finish, I expect a slightly sharper and longer lasting edge but in use I doubt there would be a noticeable difference.

Enough fun, time for the monkey suit and strapping my butt to a dark box for several hours.

ken

[Kees Heiden]

If someone could explain what burnishing is it would be appreciated. Must be my frenchglish!
Normand

Burnishing happens for example when you slide a ball (for example a sharpening grit particle) over a steel surface (the chisel edge) with enough pressure to exceed the yield strength of the material. When you exceed the yield strength, the material doesn't react elasticy anymore, it deforms permanently. In other words, the deformations don't jump back after the passage of the ball, they are permanent.

If the grit particle has sharp edges or corners, then it works with a cutting action, it makes a groove and really removes material. If the grit particle is rounded (and it is hard enough) then it also makes a groove but the material isn't removed, it is smeared aside. With a bit of luck you smear the tops of the grooves into the valleys, and thus make the surface smoother. You also make it harder.

I don't know if that really happens when you use a fine Arkansas stone that hasn't been dressed for a long time. I also don't know if it desirable or not. In theory it doesn't sounds too bad, so I am curious if Stanley has other information.

I don't think this happens with synthetic waterstones, because the surface of the stone is continually refreshed, so you always have fresh grit particles. With all the talk about slurry building I also think burnishing doesn't really happen with natural water stones, but I could be wrong. The grit particles of natural waterstones are not very sharp to begin with. But when you grab an old, dished, black Arkansas from a long forgotten toolbox, then the chance that it hasn't been dressed in a loooong time is likely, so burnishing could be real.

Edit: I think there is another kind of burnishing which happens when the stone is fully loaded with steel swarf and doesn't cut anymore.

[Brian Holcombe]

Thanks Brian and Stan, this is the information I have been missing, which explains why and how natural stones may actually work to provide a very good or excellent final surface. Stan thanks for your extensive effort here to demystify these stones and the methodology to use to get the most from them. It all makes sense in relation to those other "truths" I have clung too in regard to sharpening. Stan thanks for warning me of the edge of the rabbit hole. I worry about that smoke up the skirt too, IMHO there is always a great deal more theory than fact. Even the best theory eventually seems to find variations that are even better....

I am wondering if a similar final result can be achieved with very hard ceramic stones like the Spydercos and green compound? I am guessing this is debatable. It may be that the nature of the fine but still sharp particles in these man made stones tends to cut or rub off softer steel vs pressing it between carbides?

Brian, I try to sharpen with a similar methodology to yours. I try to sharpen before my tool gets completely dull, at the time I can feel it slowing down/meeting more resistance..It takes less time and allows me to use a sharper blade more of the time for a similar amount of sharpening effort. Short breaks from the work do not interrupt ones flow whereas sharpening very dull tools can.

Thanks for the replies, sorry to steer a little off course Brian.

Mike, I believe that is why George tends to wear in his green compound. I don't want to speak for George on the off chance that I am misremembering, but maybe he will comment.

I never mind if my topics go well of course, it's part of the fun.

Very interesting theory Stan. I think you have done a good job of explaining the process and result. I do find your conclusion about round particles leading to the misty white color and grey matte finish or not because my initial thought would be that sharper points would lead to finer scratches and thus the milky appearance - who knows without a SEM study? I have a question though and it ties in with Brian's initial postings and or video and your description. Do you tend to use the final stone with a slurry built up on it or just clean with water. I recall Brian mentioning that he develop a slurry although I don't recall if this was for the coarse work or the final steps.

Pat, WRT the slurry, I slurry all of the finish stones. However I would like to add some comments.

With a medium or rough grit stone they build their own slurry very quickly, so in order to maintain a flat bevel on a chisel or something of that sort I let them build their own slurry. If you have ever used an India stone the effect is somewhat similar.

With medium fine or fine stones they're usually slow to slurry in my experience, so you can let them build their own slurry but I prefer to speed up the process and build one, that being said the finer the stone the finer the slurry. Most people would probably not describe what is happening on my Nakayama asagi as a 'slurry' at first glance, but it is one it's just incredibly light.

Brian,

I can't answer ease of use for the Nakayama just yet. It is too new and I'm still getting use to it but I just sharpened one of my #2 White Steel push chisels using the Kiita and finishing on the Nakayama. The Kiita finish was more than adequate with no lined up scratches to the edge, the chisel was good for anything you could ask of it. The follow up with the Nakayama just refined the matt finish, I expect a slightly sharper and longer lasting edge but in use I doubt there would be a noticeable difference.

Enough fun, time for the monkey suit and strapping my butt to a dark box for several hours.

ken

Ahh, the Nakayama took some time for me to get a handle on, just one word of caution (or to be aware of) it's the only stone I've had that is so hard that it actually became convex from regularly use with a 1200 atoma, so I check it for flatness now every so many uses. It's a handy stone to have if you need that extra fineness. I use it on my sushi knife and that thing zips through fish. I bet if you used it on Steve's smoother it would turn a piece of cypress into a mirror.

[Patrick Chase]

According to Ron Hock, and consistent with other studies I have seen, synthetic stone particles, being sharp and jagged, tend to plow furrows that are deep and V-shaped with walls sloped at relatively uniform angles, and narrow bottoms. The angled sides of these parallel furrows reflect light in a uniform manner, which explains perfectly why blades worked on synthetic stones easily achieve a mirror finish. By comparison, the rounder particles of natural stones cut shallower furrows with curved sides, and of course, rounded bottoms, diffusing reflected light, and producing a cloudy, misty appearance (at least ideally).

Appearance aside, I believe a high-quality high-carbon steel blade containing fine, evenly-distributed carbides as found in most hand-forged blades made of high-purity steel, and finished on a natural stone will stay sharper longer than the same blade finished on a synthetic stone of the same grit size. I have no hard data to support this opinion. But I believe the shallower, rounder furrows (or scratches) created by natural stones tend to support and hold in place the carbide crystals longer. This seems consistent with the SEM photographs I have seen, and feels consistent with how my blades perform when cutting wood.

The degree to which this is true is going to depend on both alloy and heat-treatment, as it's basically a stress-concentration argument in disguise, and therefore largely a matter of toughness. Japanese tools are an extreme example, as HCS tempered to Rc64-65 is extremely brittle stuff (low toughness as measured by Chapy C-notch scores etc). I therefore wouldn't be surprised if such tools' wear life is indeed sensitive to "furrow geometry" as you describe. In that sense natural waterstones may be very well matched to Japanese blades.

EDIT: It's probably worth noting that Ron Hock also uses HCS at higher-than-typical hardness (he tempers O1 to Rc62, vs common practice of ~Rc58-59 in Western tools), so his blades would probably also be unusually sensitive to notching.

[george wilson]

I repeat again,the maximum hardness for 01 is supposed to be RC 60. And,I consider that to be too hard for maximum edge retention. Over many years and many antique plane irons that I tried,back when you could get then for $2.00,I found that the ones that would hold an edge the longest could barely be files with a new,fine tooth file. This indicates a hardness of about 55 RC. Of course,these were carbon steel. However I have made very many cutting tools from 01. The ones that were too hard just would not hold a good edge. The microscopic cutting edge would break off.

[Patrick Chase]

I repeat again,the maximum hardness for 01 is supposed to be RC 60. And,I consider that to be too hard for maximum edge retention. Over many years and many antique plane irons that I tried,back when you could get then for $2.00,I found that the ones that would hold an edge the longest could barely be files with a new,fine tooth file. This indicates a hardness of about 55 RC. Of course,these were carbon steel. However I have made very many cutting tools from 01. The ones that were too hard just would not hold a good edge. The microscopic cutting edge would break off.

I agree with you that HCS tempered to anything over ~Rc60 is prone to chipping, but Hock clearly states in his book that he aims for Rc62. He also explicitly recommends tempering HCS to 325F, which is consistent with Rc62.

I should have been clearer that those Japanese tools up in the mid Rc60s are "white steel" and not O1, though it's low-alloy HCS either way.

[Stanley Covington]

Very interesting theory Stan. I think you have done a good job of explaining the process and result. I do find your conclusion about round particles leading to the misty white color and grey matte finish or not because my initial thought would be that sharper points would lead to finer scratches and thus the milky appearance - who knows without a SEM study? I have a question though and it ties in with Brian's initial postings and or video and your description. Do you tend to use the final stone with a slurry built up on it or just clean with water. I recall Brian mentioning that he develop a slurry although I don't recall if this was for the coarse work or the final steps.

The cause of the "milky" appearance was one proposed by Ron Hock on his blog, and is based on SEM photos. I have since confirmed it with a Japanese sword polisher with a somewhat scientific mindset. It is also consistent with studies I have read on, of all things, piano finishes, and how the shape of the girt and direction of the polishing (circular versus linear) can greatly impact not only the shininess, but even the perceived color of the black lacquer. But I have not done scans myself, so I present it only as a theory.

The slurry is absolutely essential, especially for the final steps. And you should gradually decrease pressure.

Stan

[John Kananis]

I use it on my sushi knife...

OK, that's it; you make sushi too - I'm in Jersey; I'm coming by to hang out... :-)

[Patrick Chase]

OK, that's it; you make sushi too - I'm in Jersey; I'm coming by to hang out... :-)

Nah, he merely said he has a sushi knife. Actual use of said knife hasn't been established. Tool-junkie-ism isn't limited to woodworking you know :-).

[John Kananis]

Nah, he merely said he has a sushi knife. Actual use of said knife hasn't been established. Tool-junkie-ism isn't limited to woodworking you know :-).

Tell me abut it, you should see my electronics labs, lol. Still want sushi, haha.

[Brian Holcombe]

LOL, John! ...My sushi making is hit or miss, my speciality is truly barbecue ribs, steaks and burgers.

Sashimi is fairly easy, good fish and my cutting work is fairly reliable, but I'm fine tuning my rice recipe (I realize that is sort of the life long goal of sushi making).

[John Kananis]

Barbecue, ha? In that case, you're coming to my place (I have a restaurant in Essex county and we grill on 1000 degree+ charcoal - our salmon is sushi grade too) but you have to be good with Greek food (real Greek food, no gyro!).

EDIT: Loving those chopsticks

[Mike Holbrook]

I can't believe you people are off topic on Que....whoever went off subject might need to be flayed, ohh wait.... I am more of a low, looong and slow guy, brisket, chicken, pork butt, ribs, hardwood charcoal and my own apple wood. It takes me at least two days to make serious Que. I hope you people know how to make slaw, because eating Que without slaw is just uncivilized. Steaks, now that is where you need a little more heat....

The Spyderco stones seem to work differently to me. They leave more residue on the stone with more of a "greasy" texture. The steel seems to smear across the surface of the stones. My Sigma Power Select 2's seem to work more like I think the jnats work. Steel seems to attach to the swarf more than the stone.

I use the green compound on MDF like George and his theory of the larger particles embedding in wood or MDF or breaking up after use seems probable from my experience as well. I believe Rob Lee supported that theory in another thread. I have wondered if the smeared steel residue on the fine Spyderco stone worked something like the MDF with embedded compound. The smeared steel essentially dulling the sharp particles.

I thought burnishing implied the moving of metal along an edge with a "burnisher", as used to make a feather edge on a scraper. If burnishing can make a feather edge on a scraper, I am wondering if it might fill in between the microscopic grooves in the edge as well.

I seem to chase a "wire" edge with the fine Spyderco that the green compound might be removing.

[Kees Heiden]

I'v read that the fine Spyderco's also have a burnishing action. Likewise I read an old comment from David Weaver where he wrote about the very hard Japanese finishers, also working more like a burnisher then a cutter.

Those things are never 100% one or the other. I still see plenty of black stuff appearing on my Arkansas translucent, but it sure doesn't feel like it is cutting.

I am still very curious to hear a further explanation from Stanley that burnishing should be avoided when using oil stones.