Diamond stones versus natural stones (and ceramic stones)
- This topic has 9 replies, 5 voices, and was last updated 10/05/2017 at 2:56 pm by
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Just like the previous topic I wrote, this one originates in another thread (here), but we’ve discussed it more often. Just never structurally.
It is perhaps best introduced by a quote from Tom:
I recall some years back hearing that there was a faction of older sharpeners who complained that diamond abrasives were inferior when compared to other media. This is similar to the stereophiles’ complaints that digital music (CDs) was inferior to pure analog systems (meaning LPs and vacuum tube systems). Yeah, there maybe was an audible difference if you had really, really good ears, but you couldn’t buy a stick of gum on the difference.
One of the statements made sometimes (not necessarily on this forum) is that diamond stones cause more chipping than natural stones. (By “natural stones” I mean both synthetic stones like Choseras and Shaptons as well as true natural stones like Coticules.) I doubt this is the case, but I may be wrong.
A sharpening stone consists of abrasive particles embedded in a binding substrate. (A ceramic stone is an exception. See my blog.) The reason such a stone sharpens is that the abrasive particles are harder than the steel that is being sharpened. As far as I am aware it doesn’t matter whether these abrasive particles are only a little harder or a lot harder, like diamond particles. (Well, it does matter for the amount of steel that is removed in a particular time and thus the speed in which one can sharpen, but not for the final result as long as one takes enough time.) This is the reason I think diamond stones don’t cause more chipping.
What does matter is the size of the abrasive particles. If the diamond particles are larger than the particles in the natural stones, they will have a different effect and may cause more chipping. But we have diamond particles in all sorts of sizes, just like we have abrasive particles in natural stones in all sorts of sizes.
What also may influence the sharpening result, and this is what I am not sure about, is the binding substrate. I think that in diamond stones the abrasive particles are held in their place very well. In some natural stones, this may not be the case (?) and the particles may start “rolling around”, like on a strop. Maybe this is why some people say that natural stones polish more than diamond stones. Or maybe it is because relatively soft abrasive particles get rounded easier than harder abrasive particles like diamonds. And maybe they are right for certain stones, maybe not. I just don’t know.
Here a quote by Tom from the other topic is relevant again:
What I’m leading up to here is the fact that diamond abrasives are a form of machining – they don’t polish, they scratch. And when the grit is low and the steel is relatively fragile, pieces may break off. While this seems obvious at low grits, we don’t know at which grit level the breakage stops, or at least becomes insignificant.
What do you think?
Molecule Polishing: my blog about sharpening with the Wicked Edge
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I think the only way to get a definitive answer would be to get high resolution images of the apex on knives that were finished with similar grit abrasives of varying types. I don’t think I’m experienced enough to offer even anecdotal evidence since my primary sharpening experience has been with diamond abrasives.
Mark, this can be a tough discussion. A lot of it is based on our theory, guesses, hypothesis and personal experiences. Then the personal experiences are interpreted based again on theory, guesses, and hypothesis. Some of my knowledge has some scientific basis and a lot of it is just experiential with photographic observations of the results of using the abrasive mediums to sway my theories.
You grouped them into two broad groups, Diamonds VS Natural Stones. I really think there are at least three distinct groups: Diamonds and Synthetics Stones, the Natural Stones, and last the Ceramics. They are all, in general, as you wrote, abrasive mediums of basically hard particles suspended or held in place in or on a solid matrix.
The Diamond stones and Synthetic stones, IMO, are the most alike and most similarly rated or described. These are both man-made manufactured solids with known size abrasive material attached to the outside as is the case with diamond stones or mixed through-out the solid as in Synthetic Stones. With diamond stones the size of the diamonds and spacing determines the grit. With the Synthetic stones different hardness and size abrasive materials in a determined density determines the grit rating. The pointed or sharpness of the diamond particles removes steel as we sharpen knives by scratching it away, (machining as Tom put it) while cutting groves in the steel. As the diamonds wear, get knocked off and lose their points the diamond stone becomes less effective.
The synthetic stones, like diamonds also scratch grooves and remove metal to sharpen knives. I believe the synthetic stones are more efficient, predictable and consistent. By varying the density and size of the abrasive material imbedded throughout the solid matrix, during the manufacturing process, the Synthetic stones can be made to have a greater variety of predictable effects. As the synthetic stone with the embedded abrasive wears the stones wear away, what we call dishing. The synthetics have the advantage of being renewable by flattening them, called lapping, to bring fresh abrasive material to a level surface for continued use.
The natural stones are truly natural and are quarried from the earth like granite and marble. Different hardness, coarseness and abrasive natural stones come from different areas. These are then cut into useable shapes and flattened and polished for use. Natural stones are similar to some synthetic stones in that they form an abrasive slurry with water on the surface and this slurry is what actually removes the metal when sharpening. Some natural stones like Arkansas stones are used with oil.
Being natural I believe the grit rating is more varied and less predictable then with the man-made stones and can vary also in the same types of stones. I think there’s a mystique to sharpening with natural stone. A “Zen” kind of thing.
Last the ceramics stones are a whole different animal. They can be made of same minerals used as the abrasives in the synthetic stones but they’re melted, sintered, together and shaped into usable sharpening stones and rods. They are usually only finer grit stones and can be used dry. They also tend to be brittle and can break if they are dropped. The ceramics work because they are very hard on the order of diamonds. Rating they’re grit level can be difficult.
This is my opinion: The ability to manufacture synthetics stones with a variety of types, sizes and densities of abrasive I believe makes them more controllable and predictable for sharpening and therefore possible will cause less chipping. They are used with water, serving as a lubricant and cooling the metal surface. This may also help prevent chipping. Diamonds, called the hardest mineral, known to man, possibly with their narrow sharp points, cut deep grooves and I believe can catch on carbides in the steel matrix and being so hard the diamond doesn’t break, they break the steel matrix possibly causing more chipping. The abrasives in the manufactured synthetics stones can break down or wear off before busting the very hard carbides loose from the matrix therefore may cause less chipping.
I do think the acuteness of the bevel contributes to the brittleness and chipping of hard steels. I don’t believe these hard steels need to be sharpened to a fine polished edge to feel sharp, to cut and slice well and to be a durable edge. I have observed this with new, out-of-the-box knife edges of some of the super hard steel knives I’ve purchased. Fine grits are associated with finishing an edge, that is when the edge is its narrowest. This is when, IMO the hard steels are the most fracturable or chippy. Diamond stones as I related above are very hard and I believe with these very fine grits and narrow thin edges may perhaps cause more chipping than the less hard abrasives in the Synthetic Stones.
Marc
(MarcH's Rack-Its)Thanks for your extensive reply, Marc. I think you also gave a good analysis.
Mark, this can be a tough discussion. A lot of it is based on our theory, guesses, hypothesis and personal experiences. Then the personal experiences are interpreted based again on theory, guesses, and hypothesis. Some of my knowledge has some scientific basis and a lot of it is just experiential with photographic observations of the results of using the abrasive mediums to sway my theories.
You and Organic are completely right: this is partly a theoretical discussion (and partly empirical). Some of my knowledge, not necessarily in the area of knife sharpening, has a theoretical basis as well and I usually don’t only want to know what works, but also why it works. That can be tough, but fun too. I once read that the people who can judge steels best are the people that sharpen them. And given the level of many discussions on this forum, I certainly feel at home here.
I think you’re right that synthetic stones can be more consistent than diamond stones and natural stones and that this is one of the reasons they can be more predictable. Although I do not know how large this effect is. In addition, it may be that the hardness of diamonds can cause them to knock out carbides more easily than the softer abrasive particles (in a slurry) of natural stones and synthetic stones. My gut feeling says that this might well be the largest difference. But as Organic said, the only way to get a definitive answer would be to get high-resolution images of the apex on knives that were finished with similar grit abrasives of varying types. Maybe, maybe, the new grit chart Clay is working on will include such information.
Also, as you write, fine grits are associated with finishing an edge, that is when the edge is its narrowest. This is when hard steels are the most fracturable or chippy. We discussed this before in another topic and, obvious as it may be, it was a new insight for me back then. When I can sharpen again (broken arm) I’ll try to compare the high-grit diamond films to high-grit synthetic stones (15K and 30K Shaptons). I hope my microscope has a resolution that is high enough to show the difference if there is one. (Diamond films are a little different again from diamond stones.)
Molecule Polishing: my blog about sharpening with the Wicked Edge
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I haven’t seen a discussion on what actually happens between a blade and the slurry of a waterstone. The slurry would seem to be made up of particles of grit (and swarf) suspended in a liquid. Since the grit in suspension isn’t anchored, it can’t actually forcefully scrape away any steel. Surely the grit still anchored in the stone will scratch the steel, but the grit in suspension is doing something else. As I try to imagine what’s happening with the grit in suspension, I come to the conclusion that it’s rolling or sliding between the two surfaces. As such, the effect is (I think) a version of burnishing. This would be similar to stropping, a process where the grit is not solidly anchored. Rather than “machining” the surface of the steel, the grit particles are rubbing the steel surface, a process where the surface is deformed, but not scratched. The deformation has the effect of polishing the surface of the steel. If you’ve ever cleaned up a piece of rusty steel with a wire wheel, you saw that as you made progress, the surface of the steel not only is cleaned, but it is also getting shiny – a more typical version of burnishing. The steel wires aren’t appreciably harder than the steel being brushed, so they can’t really remove steel. They can, however, beat the crap out of the steel surface, pounding the irregular surface into a more uniform surface.
If you’ve been using diamond film with a microscope, you’ve probably seen instances where you’ve stepped from one grit of film to the next. But this new grit, doesn’t seem to be producing scratches. The surface is getting shinier, but why would 3 micron film leave scratches, but 1.5 micron film doesn’t? The difference in grit wouldn’t seem to be so great that suddenly the scratches are so minute that they can’t be seen. But clearly, there’s a big difference here, so why? I think it’s that the finer film grit, simply can’t get a purchase on the exposed ridges of steel left by the previous grit. It can’t scratch, so it is simply rubbing the surface and in doing so, creating a burnished effect. We call it polishing.
Now I’ll take this a small step farther. This finer film can’t get a purchase with the steel in the field of the bevel, but maybe it can at the more-exposed edge, where maybe it produces micro-chips or scratches. And maybe it these that are cleaned up by stropping?
(Diamond films are a little different again from diamond stones.)
I believe diamond films are just diamond stones of very fine grit. At first the finest WE diamond stones we had were the 3µ stones that didn’t stand up well to use or last very long. Now we have the WE 1500 grit diamond stone that is a good diamond stone and IMO works very well. The difference between diamond stones and DLF may lie in the solidness of the physical attachment of the smaller diamond particles in the plastic film adhered to the glass platen with PSA. Again this is just my theory or hypothesis. I share Toms observation, above, but not necessarily his explanation. That subject of DLF I’ll leave in the thread where it started.
Marc
(MarcH's Rack-Its)1 user thanked author for this post.
Thanks Marc, but my post wasn’t meant to be about DLF vs diamond stones. It’s proposing a theory that when the grits get too small to produce significant scratches, they begin to behave like a slurry – rubbing, rather than scratching – and thereby polishing. But what I am really interested in is what happens at the edge – and does this explain why stropping seems to produce a sharper edge?
I understand that Tom, and your theory is very interesting and valid. I didn’t mean to cut you off or shut down your point. I was just thinking that we have so much good information we’re collecting through shared experience, on Diamond Lapping Films in this specific case, that it may be better served to try to keep the subjects consolidated to make it easier for our forum information searchers to find the information all in one place.
“What’s happening at the edge” is a very good title and subject deserving to have it’s own thread. If we really knew what’s happening there we’d answer a lot of the questions about how best to sharpen different steels.
Thanks, Tom and please forgive me.
Marc
(MarcH's Rack-Its)From our own tests and from Todd Simpson’s SEM images about stropping, I think the main reason the edge gets sharper when stropping is that the strops pull the metal up into a peak with a much narrower cross-section. I imagine it like pulling up whipped cream or meringue with a spoon. The small cross-section further concentrates the force behind the knife, making it cut more efficiently. Stropping even improves toothy edges for the same reason as well as helping to comb all the micro-teeth into a line.
-Clay
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