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Quantifying Sharp

Definitions of Sharp and Keen

Sharp and Keen part 2

A Comparison of Several Manufactured Blades

The Bevel Set

The Honing Progression

The Diamond Plate Progression

It’s too big of a jump!

SWARF!

Abrasion rate vs “Grit”

What is a Burr? – part 1

What is a Burr? – part 2

Burr Removal – part 1

What Does Stropping Do?

Abrasive Particles Under the SEM

Optical vs Electron Microscopy

Diamond Plate break-in – part 1

Diamond Plate break-in – part 2

The Pasted Strop – part 1

The Pasted Strop – part 2

The Pasted Strop – part 3

The Pasted Strop – part 4

Simple Straight Razor Honing

Dulling on Glass

Does Jnat Slurry Break Down?

Jnat Slurry – part 2

The Barber Hone

Sharpening on the King 1k/6k combination stone

Ceramic Blades

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106 responses to “Home

  1. Recently a question came up on a woodworking forum that recurs from time to time, and seems to get different answers without much supporting data. Namely, will “better” steel get sharper, or will it simply maintain an edge better. Can you shed any light on this, perhaps comparing a few tool steels with the same sharpening regimen, preferably one that would be used by a woodworker.
    http://www.ukworkshop.co.uk/forums/does-better-steel-get-sharper-t89727.html

    Thanks
    Bridger

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    • We know that a simple carbon steel, properly heat treated, can take an extremely keen edge; one so fine that it is damaged by simply cutting paper. In other words, we can form an edge that is sharper than we can possibly use.
      Therefore, we must consider edge retention in this discussion. We then have to define what we are cutting, and how the edge dulls/fails during use (blunting, wear, chipping, etc). A “better” steel would be one that resists the relevant wear mechanisms. The properties that make the steel “better” in terms of retention may limit the initial sharpness. This then becomes a very complex question.

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  2. Todd, can you please give some quick advice based on your experience?

    I follow your regimen on stones, and after coming off the 8k, I go to hanging denim with CrOx (as opposed to AlOx), and then .25 diamond paste on smooth leather, then 30-50 laps on latigo.

    Should I strop on clean mesh/linen in between CrOx and diamond paste? Should I switch to Aluminum oxide instead of CrOx?

    From a qualitative point of view, I do get smooth shaves already with no razor burn or irritation. But maybe it could be better. I’d really value your feedback. Thanks!

    Liked by 1 person

  3. Polishing compound “crayons”.

    We’ve all probably bought and used them at some point. When I started sharpening knives, I rushed out and ordered a 6-pack of Enkay (various colors) off of Ebay to use on a home-made paddle strop.

    Based on what I’d seen from a guy on Youtube, after 2-3000 grit stone edge leading strokes, I would strop with a motion that start at a low angle and end about 30-40 degrees, “medium presure”, on flesh side (furry), using the “green stick” of compound. What I found was that I was getting a level of keenness that was unexpectedly high. Not only that, but the durability of my kitchen knives, or the time I went before needing to re-sharpen, increased roughly 10x. I use a nylon cutting board.

    I haven’t bothered using any other compounds, or colors, from that original Enkay pack. One would assume that Hand American, Enkay et al. use similar “grits” or formula so that the standards for this color system are somewhat the same.

    I would LOVE to see what exactly goes into these compound crayons, or at least view the abrasive particle sizes for each color. After becoming familiar with all of your material, I would assume that Enkay green has a decent amount of Aluminum Oxide in it. I think it would greatly benefit the sharpening community to have a better understanding here.

    Thanks!

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    • Green is almost universally Chromium Oxide, particle size can range all over the place with those sticks, but it’s often described as .5 micron. Different manufacturers may add other abrasives into their sticks as well though – there’s no way to say for sure what exactly it is short of asking the maker or Todd-style analysis with SEM or other high technology equipment.

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  4. I hope that Todd covers “stropping on paper with compound over stone” one day and uses 1, 2 etc layers to see how microconvex it gets and whether we see a burr or not and how this compares to denim with Alox und subsequent leather with Diamond.

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  5. Your honing method for straight razors has worked wonderfully for me, thank you very much for making it available.

    Apart from straight razors, concerning the sharpening of plane blades and chisels, do you think this same method would be advisable, or should it be modified somehow (aside from beginning with a coarser stone like 1000#)?

    [for wood working tools] There is the belief that the large particles of coarser stones at the same time as they abrade the edge, they create microfractures or tensions that even if polished on the surface leave the edge fragile and prone to failure. There is also the belief (it would likely be more than simple belief) that Japanese natural stones leave longer lasting edges than synthetic waterstones, but there is no clear explanation about that.

    Do you have any insight on these subjects, or have you tested not only the attainable edge but also how does it actually perform under stress? It would be great throwing some light about the edge resistance between synthetic stones, natural stones and micro convexing with pastes.

    Last, if those microfractures affecting the edge integrity were real, would they be equal with edge leading vs edge trailing strokes? And their depth would it be such for being able to remove them with denim strop + paste?

    Thanks!

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    • I have only used this approach once on a plane blade, and 2 or 3 times on chisels. As a very occasional woodworker, I was pleased with the results, but I simply don’t have enough experience to draw any conclusions. The one issue to be aware of is that the amount of micro-convexity increases with pressure (obviously we want to minimize this).

      One of the great advantages of micro-convexity is that we remove the steel from the apex that is damaged by the stone.

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  6. Hi,
    Amazing work!!!
    Some questions:
    – Do you have pics of Kyocera ceramic edge? I saw some comments that shaving sharpness is possible, however the practicle size is 1 micron. Theoretically it can be done with diamond film to break these to form a 50-100nm edge, but never saw any SEM pic of this. The great advantage of ceramic is that it can not make burr, however obviously it will chip. Also would be good to see pics after some run on cardboard. In theory the chipped edge is still good for longer time than any steel, but would be perfect to see some hard facts 🙂
    – Did you make any tests with differetn steel types? I think the 50-100nm sharpness is achievable with any steel, the “only” difference is how long they keep that edge. Obviously this can be very time and resources intensive test…., so just the most popular metals would be tested to see if they can really make that low nm edge. E.g. I have some doubts that PM steels with large grain are able to make it. Personally I feel that they can be sharp, but very quickly degrading.
    Thank you for your blog, showed many extremely valuable info,
    Best

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    • Ceramic blades are on my (long) list of things to look at. I have looked at a few steels (several are shown in various articles already posted). Steel “type” is characterized by features at the 1 micron and larger range, much greater than the apex dimensions of a “shaving” sharp blade.

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  7. Todd, you have a slide of an edge after only 3 passes I believe on CBN that makes a huge difference. As I look through the entire blog, I can’t find it. Do you remember where it is? Thanx

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  8. For straight razor honing do you use a different progression of stropping / honing than you will use on a knife blade? ……….. What do you use for each ….. and what progression of abrasives hones / strops do you use? ………. Do you have a simple formula for a simple-mind like me? ………..

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    • There are many ways to sharpen a knife, and most recently I have been using the same approach as I do for straight razors.
      Assuming the knife has already been thinned below 30 degrees and just dulled from normal use, I typically use a 1k stone/hone followed by the metal polish on hanging denim and some sort of leather strop with sub-micron diamond or CBN. For a straight razor, I would use a 4k stone rather than a 1k.

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  9. We have recently had some discussions on an ice skating board (e.g., http://skatingforums.com/index.php?topic=7339.0 ) about a technique that some skate techs use in sharpening skate blades. In particular, rather than deburring the edge, a few sharpeners like to repoint the burrs downwards into the ice, to increase lateral resistance to sideways skids. While quite fragile, such edges act more sharp. I have played with such things, using simple hand tools. But some people question whether such a thing is even possible. Have you played with pictures of such blades under an electron microscope? Thanks!

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    • I don’t know much about skate sharpening, but I would expect that at the range of apex angles you are working with, the burr will break off fairly easily if you leave one.

      When you sharpen a knife by forming a burr and breaking it off, the edge will typically feel “toothy” (as with the Murray Carter “three finger test”). If the burr is removed to form a relatively keen and uniform edge, it may not “feel” as sharp or pass the three-finger test.

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  10. It does break – or more often bend over sideways – easily if you walk on the rubber mats around most rinks without wearing “blade guards”. If you deburr the edges, and maybe dull them a little, the edge becomes much more durable, though it feels less sharp. But ice itself, at ice rink temperatures, is somewhat soft. But many skaters love skating on very sharp blades, so a fair number of skaters do this. It’s particularly common in the speed skating community, though it should be noted that serious speed skaters often re-sharpen before every race heat.

    It’s a trade-off: people often say that deburred edges glide better, but push (pushing is approximately lateral, not along-track) less well. In addition, if you sharpen, then deburr and dull a bit, sharpening, as long as it is done often enough, doesn’t alter the feel of the blade as much, so some competitive figure skaters prefer that style.

    I’ve looked at sharpened skate blades under a 50-100x $30 USB optical microscope camera, but the pictures you produce much, much better. Much clearer, much more 3D looking. I imagine your electron microscope cost somewhat more than $30… 🙂

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  11. Sorry, I should have proof-read that.

    To clarify, those few skaters who use extremely sharp blades do not deburr or dull after sharpening. But most professional skate techs (for hockey and figure blades) do deburr somewhat.

    Also, ice isn’t really soft, unless you count the top few hundred Angstroms, which are probably liquid at ice rink temperatures – but I don’t think skate blades receive comparable stress to that required to cut across hardwood grains, or to cut metal.

    BTW, I don’t understand why razors dull so quickly. Isn’t hair soft?

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      • I guess what I was really thinking is that hair is flexible (perhaps because it is thin).

        Which actually makes hair hard to cut, because it bends out of the way, limiting the amount of sheer force available to break its chemical bonds. So it works exactly opposite what I said.

        (I presume a razor cuts hair while shaving through sheer, like a scissors, because the apex isn’t thin enough to get between the bonded atoms. I.E., the hair root is held in place by the skin, while the razor applies a sideways sheering force, which, like any sheer force, pulls apart the bonded atoms, and also changes the inter-atomic angles away from the orbital angles at which bonds for those atoms can occur. Both effects break the chemical bonds holding the hair together.)

        If sheer, not compression, cuts hair fiber while shaving, a razor apex doesn’t need to be thin to increase the pressure (force/area) on the area of contact. Instead, a thin apex reduces the distance between the bound hair root which holds the hair in place (and somewhat confines the orientation of the base of the hair), and the closest place the blade applies a sideways force, increasing the sheer stress.

        Likewise, perhaps shaving cream and wet skin don’t really “soften the beard” in terms of making the hair easier to cut. Instead they allow the blade to slide against the skin smoothly without damage even if you press the blade into the skin, again decreasing the distance between the root and the sheering blade, again increasing sheer stress.

        Did I get it all right this time?

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      • The outer shell of a hair is composed of hard keratin plates that allow it to be flexible, but these plates are quite hard (like fingernails). Shaving will occur when the blade “catches” an irregularity in the shell of the whisker (edge of a cuticle plate, for example) and then penetrates shell and is pulled through the hair. This generally requires the apex to be on the order of 100nm (0.1 micron) or less to achieve sufficient pressure. The severing of a hair is simple push-cutting, chips in the blade will produce striations in severed surface of the whisker.

        https://scienceofsharp.wordpress.com/2015/03/24/sharp-and-keen-part-2/

        When hair (whiskers) absorbs water or oil they generally become more flexible and much easier to shave. I don’t believe the individual cuticle plates soften, but rather the plates more over each other more easily when lubricated. Maybe teenagers or people with the beards of teenagers can shave dry, but it has been decades since I have been able to shave without having a shower first.

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    • The primary difference between skates and razors is the bevel angle. A razor will be in the range of 20 degrees (inclusive) while I would guess skates (depending on the ROH) would be more than 60 degrees.

      A burr is the result of steel bending or “flipping” from one side to the other to “avoid” being abraded. For a razor, this only requires a 10 degree deflection each way and most steel can accommodate this without much damage. For a skate blade, the burr will be deflected more than 30 degrees each way and so the burr will consist of damaged/softened steel and this burr will likely torque the apex below the burr, causing damage to it as well. This is not necessarily bad if the goal is to break the burr off and leave an irregular (rough) apex. With a knife, a broken off burr will typically “feel sharper” than the more regular, keener apex resulting from de-burring by stropping.

      Razors can dull, but more often (at least with straight razors that have smaller angles than commercial blades) the damage results from micro(nano)-chipping due to lateral forces. With the large apex angle of an ice skate, the dulling will almost certainly be blunting due to abrasion and polishing of the apex parallel to the blade.

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  12. I probably still oversimplified. In particular, even if sheer starts the tear/cut, other forces might continue it. For example, my approximation only considers the bottom portion of the blade, and would suggest that the top surface, and its thickness, are irrelevant. I also didn’t model the interaction of blade shape and tilt, with skin – e.g., bumps and cuts.

    Also, compression, sheer, tension and torsion might only be macroscopic approximations that don’t adequately describe the quantum physics of microscopic level motions and stresses.

    So maybe I should just try to empirically determine how to sharpen blades to shave better (and skate better), and ignore the physics of shaving (and skating).

    In that vein, I’ve a very practical problem. As I’ve aged, my hair has gotten thinner and harder to cut. Electric razor cutters only remain sharp enough to work at all for about a month. Disposable Bic (sensitive skin) razors work slightly better, for one day or sometimes two. And so far I’ve been unsuccessful at making a ($5 to $10 stainless steel) straight razor work even as well as either. 😦

    I haven’t tried your sharpening methods yet. You’ve definitely used fancier tools than me. Maybe something in your page will give me a magical answer to my fine hair shaving problems.

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  13. I love the “edge view” images you show. They show edge defects so clearly, and are some of the most beautiful scientific imagery I’ve seen. (It might be good enough to enter into the “science as art” competitions.)

    That seems to requires a pretty wide depth of field, right?

    John D. Verhoeven, in

    http://www.bushcraftuk.com/downloads/pdf/knifeshexps.pdf

    (an artical others have cited here) says that optical microscopes are of limited usefulness for examining knife and razor edges, because they have poorer depth of field than SEMs, at high magnifications.

    Do you agree?

    Alas, SEMS are a bit pricey for the average person. Is there any way that you can think of to use relatively inexpensive optical microscopes to evaluate edge quality?

    Is it purely a matter of simultaneously focusing different parts of the image?

    Thanks.

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    • I don’t agree that depth of field is of great consequence in this application.

      The issue with optical microscopes, even ones costing as much as a luxury car, is that they cannot resolve features at the relevant scale. Optical microscope can still be useful, but we must understand that we are making indirect observations, for example to determine whether scratches terminate before they reach the apex.

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  14. Todd,

    I don’t know if this is the right page to post my question, so please move it if not.

    Something that has intrigued me for some time is the ability of my Thuringian stone to hone ZDP-189, quite contrary to my expectations; This because I believe that the abrasive ingredient of this stone is softer than the chromium carbides in the steel. Microscopic inspection @40x reveals no relief polishing of carbides and a near mirror polish.

    Any ideas as to the action/s involved?

    Cheers
    John

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    • The “harder” carbides are wear-resistant, not wear-proof. The carbides will limit the abrasion rate (how long it takes to sharpen) but they will not sit proud of the matrix by more than a small fraction of a micron as they prevent abrasion of the matrix until they are abraded themselves.

      This is an image of an S30V blade stropped with aluminum oxide metal polish – you can see the carbides are slightly proud of the matrix.

      s30v_edge_02

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    • The problem is that it takes far longer to assemble one of these articles than it does to do the experiments and take the images.

      I do have several results that I hope to find time to write up in the next few months.

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  15. Gentlemen,
    I love this approach to understanding sharpness / keenness and would very like to perform a similar study albeit with a reduced scope.

    I plan to document the surface expression of sharpening steps from initial bevel setting to final stropping of a good quality chef’s knife. I have a new Edge Pro Professional sharpening system and will buy a good quality metallurgical microscope equipped digital imaging. I have a scientific background but only peripheral knowledge of microscopes.

    Thus, I NEED HELP SPEC-ING / CHOOSING THE MICROSCOPE.
    Can someone please point me to an expert on that type of microscopy?
    Karl Gunter
    Sugar Land, Texas

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    • Kari,

      I think you would be better served with a low power, say up to 50x, maybe 100x but not higher, stereo microscope.

      In practical terms, there is little to gain by viewing edges above 50x, unless one can access a SEM.

      Cheers
      John

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    • Karl,
      An optical microscope will never be able to resolve the relevant features directly, but we can indirectly determine what is happening in many situations.

      I think you would be better served with an inspection microscope than a metallurgical microscope.
      I would suggest a trinocular stereo zoom microscope with a ring light as well as a incident light than can be adjusted to glancing angles. There are “consumer” grade microscopes like Amscope that are reasonably affordable.

      http://www.leica-microsystems.com/science-lab/factors-to-consider-when-selecting-a-stereo-microscope/

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      • John,
        Thanks for the follow-up. You might think that your observations / advice is sooooo basic, but its exactly what i need. The link to the leica site taught me a lot.

        Yesterday i went a great lil microscope, telescope, marine instruments shop in Houston (can i give their name on this site?). Their primary biz seems to be repairs, adjustments, etc but the also sell new and used instruments.

        Les Swift spent over an hr with me putting my never used Kasmui “standard” 8″ chef’s knife under 2 different scopes: a 45X stereo and a standard binoc reflecting light unit. As you said, the stereo showed the abrasive tool marks beautifully, whereas the higher power standard scope was able to show better edge detail (honing?)

        Today, Les has a 200X Olympus unit set up, says he put a razor blade under it and got great detail. I’ll go there this afternoon.

        This stuff is so much fun, i can barely contain myself 🙂
        Thanks again for your help

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      • John & Todd
        I much appreciate you guys taking the time to respond, give advice.

        After looking thru both the 50X stereo and the 50X (min) metallurgical it was very obvious that the stereo’s view was WAY, WAY better at discerning surface texture than the metallurgical. It was also evident that at 200X and even 400X the metallurgical scope saw things which were just too small for my un-educated eye to pick up on the stereo. I am not being hard-headed in buying the metallurgical first, i intend to buy a used stereo after a while.

        Les & I did experiments with incident light rather than thru the lens and yes indeed, features became visible as the light direction changed. So i got a two headed goose-neck, LED lamps. The stage on my “new” Vanox is very large with X-Y verniers and 270* rotation.

        I have just started this and already saw something i never would have guessed. The brand new Kasumi has abrasive scratches which are very coarse, then just the very edge looks like it was finely honed at a little greater angle than the primary bevel. I had thought the whole bevel was routinely brought to a finer and finer surface???? Maybe i am interpreting this “scratches” incorrectly? Anyway, revelations like this are exactly what my project is all about.
        Please be patient with my ignorance, i mean well 🙂

        BTW: for some reason i didn’t see Todd’s remarked until John re-posted them???

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  16. John,
    Thanks much for your rapid reply; just pointing me at a stereo scope is helpful.
    Could you very briefly tell me why the stereo scope is preferred?
    BTW: i am scheduled to look at a used Leitz stereo scope this afternoon. Of concern, it doesn’t presently have a dedicated digital camera, thus one of the eyepieces would have to be removed to take pix.
    Thanks again,
    Karl

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    • Hi Karl,

      Optical microscopes have very limited depth of field focus at higher magnifications, hence the need for SEMs in this kind of work.

      Also, at higher magnifications one can only see a very small portion of the edge, whereas at the lower end, a more representative portion can be observed, giving more feedback.

      Incidentally, congratulations on your Edge Pro Professional, a very good system indeed!

      Cheers
      John

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      • Hi John,
        my “project” is defined below. This is fun for me, but i’m kinda serious about it.

        1. KDG learn about the kitchen knife sharpening world (John Harper material for hi mag pix & explanations)
        2. Learn to use the Edge Pro sharpening system using my generic 8″ chef’s knife
        3. micro-photograph the sharpening stages w/microscope equipped with a USB camera
        4. Document the surfaces, grit, bevel geometry, edge smoothness of my old “Chef’s Choice” vs my new “Edge Pro”
        5. Measure cutting effectiveness of my test knife done with “Chef’s Choice” vs my new “Edge Pro” (how?)
        6. KDG make a knife blade “sharper” than my friend Alex Batard’s best free hand effort
        7. micro-photograph Alex’s best efforts, compare w/my best result
        ?8?. learn different knife geometries & measure effectiveness, e.g. Japanese chef’s knives

        I have a USB “scope” which gives pretty good pix at about 70x, but i will get an optical scope. Your advice is noted about 50X-ish being the most useful, and the worst case i could buy a scope whose higher magnification isn’t used in the end 🙂
        Thanks for being patient with me,
        Karl Gunter

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    • Hi Karl,

      Any decent optical microscope that goes up to 50x, or thereabouts, is infinitely better than no microscope at all. However, stereo microscopes are more convenient to use. This will explain it better: https://en.wikipedia.org/wiki/Stereo_microscope

      I think that you are doing the right thing by buying one, because in my opinion without one one can never account for the sharpening results obtained with any certainty. In fact, I would go as far as saying that the microscope is the second most important tool in a sharpener’s kit after the abrasive.

      Cheers
      John

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      • John,
        thanks again for your thoughts.
        After visiting the “used microscope store” 3 times and looking at my unused Kasumi 8″ chef’s knife under both stereo and metallurgical scopes i am pretty well convinced i eventually want to have both: 1) hi mag metallurgical, 2) and a 50X stereo scopes.

        I also now know that good new scopes are perhaps outside my budget, and that looking for used scopes is like a treasure hunt, gotta be flexible. I went into the microscope shop yesterday, sure i was going to buy their used 50x stereo . However, Les had found a 20year old Olympus Vanox trinocular, 10X eyepieces, 5,10, 20, 40 objectives, thru the objective lighting. It must weigh 20-30#! On it, I saw edge features on my Kasumi i had no idea were there, so i bought it :-). They are gonna tweak it and mount a 5MP Moticam camera. I should have it home in less than a week, then the fun begins as i learn how to use it correctly.

        Thanks to you guys for all the advice!
        Karl

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    • Hi Karl,

      From what you wrote, it would appear that the lowest mag on that microscope would be 50x. Is that right?

      If so, that is not what you want, because you need to go down to 10x or 20x as well. Also, you do not want a fixed stage, rather just hold the blade with your hands and manipulate it around, so that the light strikes it from different angles to reveal the scratch pattern and edge formed in full.

      And then there’s the matter of through the objective lighting, which again is not what you want, incident light being better in my experience.

      I recommend that you follow Todd’s advice.

      Cheers
      John

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  17. Let me first say that I deeply appreciate your work here, i find it a more valuable source on information than just about any other site for any of my many hobbies. I am very much a DIY and knowledge-based hobbyist and this fits the bill perfectly.

    You have made made passing remarks about the capabilities of Belgian coticules as well as name dropping your acquaintance with the guys at coticule.be, but you have yet to provide any SEM imaging of the results (IIRC). I have read much of the information on that site, but am left with the desire to take the hypothetical and make it real and observable. Do you have any plans to publish a coticule-focused article? I would love to see images of basic coticule honing, from post thick slurry all the way to “water-only” in even increments. I would love to see the changes on and off slurry going edge leading has versus spine leading. I would be interested to see what, if any “micro-convexing” occurs naturally or is recommended afterwards. I would especially love to see you attempt to optimize the process and get an exceptional shaving edge from only a coticule and whatever various loaded/unloaded stroppings seem to compliment and finish the coticule honed edge. I would love to see some SEM images of a coticule honed edge produced from two very “different” feeling coticules, to get an idea of the edge variance we could expect from their natural differences. I feel as though the information already provided on this site enables me to make educated guesses about many of these results, but there isn’t anything like the feeling of true discovery and measurement!

    Thanks again!

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  18. Todd,

    From time to time I read of someone advocating the sharpening of cutting implements parallel to the edge, as opposed to the customary transverse (to the edge). usually, but not always, this is done because the edge is too wide for the stone, as with wood plane blades or scandi ground knives.

    Have you ever examined an edge under the SEM sharpened this way?

    Cheers
    John

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  19. Greatings Todd,
    I’m a pasionate straight razor user and restorer with an acute interest in hones and honing…I wanted to ask if there is any way you can help shed some light on a cerains hone…There has been lots of talking and debating about a certain Lidian hone lately…some people are selling them on groups and forums for a handsome price… claiming extremly fine grits … some even up to 50000.
    I got curious and got one for testing … i was not impressed….in my testing it showed little to no cutting power especialy on hard steel…but more of a burnishing effect…
    Is there any way you would be interested in looking into this type of hone and perhaps testing it and giving it a fair trial?

    Thank You!
    Best regards from Bucharest,
    Dr. Ovidiu Cotiga

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    • Ovidiu, I’ve analyzed samples of all the common natural hones, and not found anything that interests me enough to continue looking at other variants. I believe that assigning grit values to synthetic hones is problematic, and assigning grit values to natural hones is beyond the pale.

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  20. Dear Todd , if you can make some pictures of obsidian or flint chips edges so we can look into our past blade tech..prior steel times. The obsidian edges can get a magnitude sharper than the steel ones they say. You can clarify the myth . best wishes Z

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  21. Dear Todd,

    there is that old advice, that the edge of a straight razor will last longer when it is not used every day (7 day razor sets).

    The modern interpretation is that the steel may get deformed on microscopic level during a shave, introducing stress/tension to the steel which will get relaxed/relieved after some time.

    Exposing the edge to stress (stropping, shaving) before the edge had time to relieve would damage/fatigue the edge.

    Did you ever encounter any of those effects?

    Best Regards
    Borsif

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    • Anecdotally, I haven’t observed any difference in longevity between blades used daily until they need honing and alternating blades from my 7-day set box.

      I have looked at foil edges in the SEM and observed no evidence that they “realign” over a period of hours to a week.

      If there was some annealing effect occurring at a time scale of a day, we should also expect a difference between rinsing the blade in hot water vs cold water, or even a difference between summer and winter room temperatures.

      I tend to agree with the consensus that this is advice invented by razor salesmen.

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  22. Thank you, I greatly appreciate your empirical investigations. Knowledge like this is empowering for practical effectiveness. I have obtained considerable empirical knowledge to guide my home knife sharpening and use.

    There are many practical applications of sharpness where accurate empirical knowledge can benefit. When I think of all of the cutting done around the world it is such a fundamental of life. If you want to branch out from razors, I think it could be of great benefit to get some your type of empirical knowledge for some of the most wide applications such as say the kitchen chef knife in cheap stainless which is used so widely by so many and by many accounts it does about 90% of the cutting in many home kitchens.

    Cliff Stamp has done some investigations on kitchen steels, one in particular on a 420J2, $1 or $2 kitchen knife. I find these investigations very interesting as the sharpening techniques are very simple, on cheap stones, and result in long term practical ‘kitchen’ sharpness. Seeing what is happening to the blade edge during his sharpening and perhaps over a month of kitchen use would be widely applicable information.

    Perhaps Cliffs ‘burr-less’ technique could be refined from grinding the apex to his 20micron visible apex more towards your 1micron technique?

    Again, thank you … having a mental picture while sharpening, actually influenced by what really happens at the apex under certain conditions, is so helpful compared to what we imagine without the benefit of SEM images.

    Like

  23. I have been doing alot of reading/research on this subject, and I had a thought…..

    At the final stages of honing/stropping, there is always a small burr on the edge….some people say to run it thru the a peice of wood on the end grain to pull it off….

    If you cool the blade in liquid nitrogen ( -196C, 77K) you take the material below its Ductile-to-Brittle transition point.

    Now either another run on the leather, or drag it thru the wood and you might do a much better job of removing that burr……your thoughts??

    Sam

    Like

    • If you read this blog you will learn that avoiding or removing a burr is not difficult. Also, I have shown that running a burr through wood generally does not pull it off.

      The issue with a foil burr being flexible is a result of the thickness, not the ductility or brittleness of the metal. This is simple beam mechanics – just as 2×4 floor joists will flex much more than 2x12s and if I take my plane to those joists, the transparent shavings will be extremely flexible.

      Like

      • Thank you for the reply!

        I am not convinced quite yet….at cryogenic temps the impact resistance also drops. So as you quickly drag the foil thru something….it may be enough to shear it off. Remember this is still a crystalline structure with very low energy so it may cleave easily at slip planes in the structure.

        Sam Sloane, B.A.Sc, P.Eng.

        Like

      • In principle, this is a trivial experiment. The problem is that the foil/burr has a very small heat capacity and minimal heat conductance to the bulk of the blade, so the foil/burr would rapidly equilibrate to the temperature of the wood block.
        Of course we could freeze the block instead, but then we wouldn’t know if any positive result is due to the increased abrasiveness of the block or the cooling of the steel.

        Like

    • I’ve tested this with mono- and poly-diamond as well as CBN and they all had the same effect. The 250ml bottle of poly-diamond suspension (814-312) is a good product, although it can be challenging to apply to leather. Usually I clean the leather with alcohol and lightly sand the surface. I use small plastic spray bottles (from Ali-Express) to apply these suspensions and then spread them with a gloved finger.

      Like

      • Thanks. I will be using an old Illinois 835 strop for the diamonds. Is it important that it be water-based spray, or can I use a different product that would make it easier to adhere to the leather?

        Like

      • I’ve used the oil-based syringe of 0.5 micron diamond from China (Badak) and it works just fine. It’s definitely easier to spread on a leather strop than a water-based product.

        Like

  24. It would be very interesting to study the novaculite, for example, the translucent hard arkansas, those stones that do not know the grain, the important thing about these stones is their density.
    They are very famous stones

    Like

  25. I have been on a week long excursion going down the rabbit hole of sharpening. It all started with a video on Reddit about a guy sharpening a $1 knife with a single bevel into something impressively sharp. That lead to me deciding I should probably finally figure out how use a steel honing rod. The internet videos and other sources I found are riddled with contradicting methods which are based on varying explanations that don’t seem to logically make sense. (ie tutorials recommending steeling with edge leading and how that pushes any deviation curves back in line).

    As a fellow man of science (albeit medical), these anecdotal widely varying and contradicting explanations obviously did not suffice. I didn’t want a chef telling what was probably happening I wanted a scientist to show me.

    While browsing around for hours I further learned about the foil edge, beautiful knife craftsmen like Bob Kramer, different techniques, stones, polishes, single bevel vs double bevel, hardness of metals, ceramics, crappy kitchen pull through setups, blades honed for draw cut vs push cut vs durability and just really the whole culture of sharpening etc.

    Lots of stuff that seems to work, but didn’t really explain (or show) in detail enough what was really going on. So this lead me to the deciding that I should search for some visual proof of what all these people were talking about, rather than just hand drawn diagrams. So I found a couple optical microscope investigations, but unfortunately even these were not detailed enough. Then I realized that SEM was really what was required for the next step up in detail. I thought the probability was zero of there actually being someone with access to this equipment who was also highly skilled with it, had the interest in the topic, the scientific mind to do it correctly and the dedication to make it all available online… I amazingly and quickly found you.

    And yes, oh my lord, Jackpot.

    I have spent the last two nights reading every post and also every comment.

    The detail and scientific rigor of your work here is incredible.
    The quality and clarity of your imaging is unmatched.
    The objective rational you have in your writing and explanations is perfect.
    And most of all the willingness to lay out new information, and in virtue of doing so challenge and disprove commonly held beliefs, is refreshing.

    Thousands of years of humans sharpening things is finally explained and visualized. And done so very well too. With all the millions of people with an interest in this I’m surprised your work isn’t plastered over every single discussion on the internet. I see this work as a trump card and proof for most topics of discussion. I’ll be sure to shine the light on the facts I’ve found here and link back here whenever I can. (btw is it crazy how many internet arguments there is regarding what’s going on and how dead set some people are about their opinion with zero proof. In the medical field we try to work solely by means of evidence based practices & explanations, so seeing others not do the same in other aspects of life is frustrating)

    So the ironic part of this newly found interest that I’ve spend several hours a night looking into is I that don’t own any high quality knives/razors/blades, I have never used a straight razor and have never sharpened anything. In fact I’ve only played around with a steel for 2 mins on a ‘too dull to accomplish anything’ cheap knife, and then contemplated using a bottom rim of a ceramic coffee mug to try some sharpening haha. But at work I always appreciate a good and perfect scalpel.

    Anyways, now that I am done praising you and framing where I’m coming from:

    1) Back to my original journey before I got sucked down this rabbit hole, any thoughts on how a honing steel rod actually works and what method is best? Do you use one in the kitchen?

    2) I didn’t see any work imaging a Japanese style single bevel kitchen knife (or single bevel scalpel). I feel having the bevel from only one side would cut the sharpening angle in half and possibly aid in improving keenness by halving the edge width. Any thoughts or plans on this topic?

    I see you are regularly inundated with questions and requests for other investigations but any response regarding these two topics & anything else I’ve said above would be most appreciated!

    Thanks for all your dedicated work here!

    – Andrew

    Like

    • Andrew, Thank-you for your interest. Your question about honing steels is timely – I am currently working on that article.

      Honing steels, rods and crock sticks provide a simple method for producing a micro-bevel to a blunted apex. I would say that they work best on a knife that has been thinned (to 30 degrees inclusive, say) since you must use an angle greater than the bevel angle for them to work. The more blunted the blade, the higher the angle required. I’ll have more to say about this in a few months.

      I don’t see anything special about a single bevel blades, in some ways they are easier to sharpen. Recently, I’ve been sharpening my chisels and plane blades using the same technique that I use for my straight razors.

      Liked by 1 person

      • Well then I am looking forward to a couple months from now. I hope you answer the questions of if it realigns vs sharpens and the method of edge leading vs trailing. Thanks!

        Like

    • Andrew:

      I’m not a real expert, but believe that sharpening techniques vary substantially with the materials and the application.

      E.g., the “steels” used on kitchen knives and pocket knives do NOT sharpen – they re-bend the (already sharp) edge to be straight again. That assumes and requires some degree of flexibility in the steel. This page seems to be most concerned with razor blades. While you supposedly can straighten some cheap disposable razors, and thereby get a few extra shaves out of them, I am not sure the high end extremely hard steel straight razors this board mostly concerns itself with are flexible enough for that to be a major issue. (Note, however, that “working” steel sometimes tends to break down and/or remove the impurity structures that make steel hard. In addition, it may be much easier to sharpen a somewhat softer steel blades – you don’t need many, many grades of hone, diamond slurries, strops, etc, like you do with razors.)

      I assume a scalpel needs to be very sharp, but need not be very hard, because flesh is soft. So a thin foil edge, made out of somewhat softer steel than is in straight razors, makes sense there.

      Likewise, at least one person on a figure skating board uses a steel on those blades to extend the time between sharpenings (skate blade lifetime is inverse to the amount of steel removed, and is therefore also inverse to sharpening frequency. At the high price end, figure skating blades have a Rockwell hardness of about 60; cheaper blades are softer. Some figure, hockey and speed skaters want foil edges, some want a blunter, more durable edge. Some hockey skaters deliberately choose a softer steel, to make it easy to create a very sharp edge, though it doesn’t last long. Figure and hockey skates are hollow (concave) ground – but not on the side, as with some kitchen knives and straight razors. The hollow is on the bottom, and serves to create two edges, one on each side. Sharpening equipment can be very simple. Can be even simpler on speed skates – can be as simple as one flat stone. Speed skaters who want foil edges grind the bottom of the blade flat, and create a sharpening lip or burr to the sides, then straighten (by 90 degrees) and polish them into edges. (Skate edges cur into the ice to create lateral resistance to motion, and also increase pushing and stopping power, at the cost of adding a little extra drag when gliding along the blade.)

      I love sharpening ice skate blades with hand tools, and have done so for about 12 or 13 years. You can sharpen figure or hockey blades with tools as simple as sandpaper glued to a dowel rod with a diameter matching the desired hollow radius, though that is hard to center properly. It’s easier with purpose-built tools. I also use a flat stone to straighten and polish the lip or burr as mentioned above, though some people grind or cut off the burrs instead – and many pros do straighten and polish them, but then dull the edges so they are less fragile. You can arguably get a better edge than with even the highest end $20,000 – $30,000 powered machine tools present in skating pro shops, and remove less metal. However, I admit the machine tools are at least several times faster, and are more practical for the professional skate tech. In fact, long blade lifetime and long times between sharpening aren’t desirable from a pro shop’s business perspective.

      Again, a sword that was intended to cut through metal armor probably couldn’t be super-sharp – an extra sharp edge used that way would break or bend. Razors are something of a special case.

      I would, however, love to have access to an SEM, or maybe even a good optical inspection microscope, to study my edges. I have made do with a cheap 200X CCD optical microscope – but it lacks the detail and depth of field to see as much as I would like.

      The SEM micrographs produced by the owner of this board are flat out gorgeous – some of the most beautiful technical photography I’ve ever seen. But SEMs are not cheap. It is a fair bet that most of the people on this board do NOT save money relative to using cheap disposable razors. I think most of them don’t start with the $5 stainless steel straight razors like the one I bought at a beauty store – they sometimes use blades costing over $100 – $200! Then they spend lots of money on a variety of grits of stones, one or more strops, diamond slurries, etc., and spend countless hours perfecting their skills. I think it is more of a hobby and personal challenge to them to meet or exceed the sharpness created by commercial razor blade manufacturers. My interest was in saving money – I gave up. I could not, with minimal equipment, and limited skill, sharpen a $5 straight razor well enough to avoid sometimes cutting myself. I went back to BIC sensitive skin disposables. (My hair is too fine to cut well with electric razors – the edges wear out too fast. Disposable razors only stay sharp enough a few days, but that is the best option I’ve found so far.)

      Liked by 1 person

    • I am curious about the person running the website. If it isn’t too personal, who are you? What is your background? Is this project a hobby, a graduate thesis project, or funded research? If the latter, who funds it? What is your final goal – to sharpen razors sharper, or to learn about the technical aspects of sharpening?

      Like

  26. Hello, to the amazing owner of this website. I want to start by thanking you. I have read and continue to read your blog to understand how to proceed on my Senior Design Capstone Project. We are currently finding a way to sharpen 440C steal blades (they look almost like a bullet with a sharp edge). we are currently working on an old microtome blade sharpening machine Shandon style and we are creating some holders to adjust to our needs. Our next step is the fun part. we are going to start testing different diamond lapping films to sharpen the blades at a 30 degree angle. the Brinell hardness is of about 50-58. what would you recommend with your vast experience in the topic as far as micron size of the lapping film and products?
    thank you again!

    Like

    • If I understand correctly, the machine you are using is for re-honing used microtome blades.
      In general, there are 3 stages to creating a cutting blade – grinding, sharpening and honing (unfortunately these terms are not always well defined).
      Grinding is the large-scale removal of metal to shape the blade and is usually done with a grinding wheel or belt sander.
      I define sharpening as putting a bevel on the blade, again this is typically done with power tools, and/or coarse grits.
      Honing, or putting the final apex on the blade can be done with lapping film, typically as a micro-bevel, but not necessarily. 1 micron lapping film would be my preference, assuming that it is not necessary to remove too much metal. However, lapping film can be challenging as it often leads to foil-burrs, particularly with PSA-backed diamond (in my experience).

      Like

      • awesome, thank you so much for taking the time to answer.

        yes, we are using an old machine to do the honing of the blade. the movement has to be slow to not create too much heat and anneal the apex.

        even at low pressure the foil-burs would form?

        i have ordered .1,1,9,and 30 micron lapping films of different qualities to do the testing. the blade approximately has .003″ of metal that needs to be removed in less than 5 minutes. our qualifying spec of “sharpness” is that the blade is not to reflect any light at 10X magnification.

        these are reefing cutting blades that are fired at a Kevlar braided rope to cut on impact.

        this project has been a lot of fun, but as you mentioned before there are very little to none studies on the sharpening of objects and your blog has been the main source of information, thank you again.

        Like

      • Sounds like an interesting project.

        3 thou (75 microns) is a lot of metal to remove with lapping film. Normally we are using it to remove less than 1 micron.

        Burrs are not the result of too much pressure, but of incomplete cutting across the apex. They can form readily on lapping film, particularly if you polish in the edge trailing direction.

        Light reflection from the apex is normally only used to determine whether or not an apex has been formed. It won’t allow you to distinguish barely sharp from extremely sharp. There is a very simple way to measure (quantify) the keenness of a blade – make a frame to hold a length of thread or fishing line and place it on a kitchen scale, then capture the maximum reading on the scale as you push cut the media.

        Like

  27. Hello Todd,

    I’d just like to say thank you for all the time and effort you have put into your research and creating this site. I have just spent the past few days reading through it and will be putting your findings into practice.

    I currently work at an abattoir boning beef. I’m always trying to improve my knives by working out knife geometry, edge honing and steeling technique. Currently there is no real set way or instruction for workers to sharpen knives just some India stones and 8 inch bench grinders and you just have at it.

    I will be trying your method up to the 3rd step as I don’t have any diamond compound for now and i will just do a clean strop. I will test one blade finished on a 2k Shapton Pro and another finished on a 5k SP, as I read in the comments you prefer to use a 1k for knives but I don’t have one and I would like to see how each performs. After I test this I should be able to work out the knife geometry to balance out the edge retention and sharpness/cutting ability.

    I also read in the comments you will be doing research into honing steels or sharpening steels whatever people want to call them. I’m very keen to see the results on this particularly after prolonged use as it is a major part of our job to use these and keep our knives going all day. No one has any real idea of what actually works. However I and a few other people who have pretty good knives, will line smooth steels with sandpaper to put small ridges kind of like a course steel but much finer, grits that seem to work for us are between 320 to 800 maybe it’s nothing I don’t know food for thought maybe?

    Once again thank you for your work and I’m looking forward to your future articles.

    Regards.
    Jason.

    Like

    • I’d be interested to know whether you prefer a blade that push-cuts or one with more draw-cutting aggression.
      Generally, all steels/rods cut a microbevel, even the smooth “butcher’s steel.” This only works for angles greater than the angle of the bevel though. I will write this article in the near future, but because there is so much misinformation on the topic, I want to be certain of my conclusions.
      I’m not clear on whether you are sanding the smooth rod to rough it up or wrapping the paper around the rod and honing on the sandpaper. I can see advantages to both approaches.

      Liked by 1 person

      • After trying several knives out over the week the push cut seemed to perform better. Both still worked well and were better than my usual but when finished with the 5k stone cutting was almost laser like. I will test out more to see if I get the same result.

        Perhaps the 2K stone isn’t aggressive enough? I do have a 320 grit stone so I will give that a go as well.

        Roughing the smooth steel with sand paper. Kind of making it like a bought fine cut butchers steel but not as agressive.

        Like

  28. I absolutely enjoy your blog, it is awesome and even if the last entry is quite old, it is (imho) by far the best source for straight razor knowledge in the internet.

    But I have a question: When I inspected my razors with a 20x loupe, I found tiny notches or chips on all of them.

    They were definitively not in the blades after honing. I also can’t see any correlation between used stones (used: Naniwas, Coticule, Thuringian, Shobudani, Ohzuku) and the amount of chips. I’m also very careful with my razors. I dry and oil them very careful after each use. I newer bump the edge against anything.
    What could have gone wrong or is this normal wear and tear?

    I can’t believe that I’ve made any mistakes. I hope you read this comment and can give me some feedback.

    Like

    • In my experience, micro-chipping is common but typically occurs at a scale below what I would expect to see with only a 20x loupe.
      It will occur more readily if you have tough whiskers or shave with too high an angle to your skin.
      Micro-chipping is a consequence of the relatively low angle bevel, and this is why I use a pasted strop to increase the apex angle.

      Like

      • Thank you very much! I rely on your simple honing method, so I strop on a “Mothers Mag” loaded cotton strop (15-20x) after the honing (and continue with 10-15 strops on 1/4 micron diamond).

        At the moment, I also guess that my tough whiskers (killing a razor edge, yeah) are a problem, especially together with a high angle. So I will try a differend shaving approach.

        By the way, I’ve got some other questions and hopefully, you make some new postings about these topics some day:

        Do you think that natural hones are “better” than good (for example) Naniwas or Shaptons? Some guys claim that synthethic hones would contain “bad” binders that would ruin the honing job. Or they claim that the abrasive particles would be sharper than those of natural hones, resulting in a “harsh edge”. In the end, honing on naturals would result in “better” edges for smother shaves. To be honest: I own a couple of natural hones as well Naniwas and I don’t see any practical advantages of the natural hones. Sometimes I think it makes more fun to hone on them and that it has some “culture” in it. But I can’t say that neither the shaves are better, nor the razors are sharper.
        Many people would also claim that a “hard” Ohzuku or a Nakayama or a Thuringian would provide a grit size of 15k or something.
        But, honestly, I think even a 3K or 5K Naniwa polishes the bevel more than my JNats, even after the entire nagura progression. What do you think?
        Excuse me for my bad english.

        Like

      • This is a complex question. There are several microscopic processes that occur when steel is removed by a hone/stone. What MAY be important the “condition” of the steel near the apex left behind by the various processes. I’m confident that nobody actually understands this, so whatever you read on “internet forums” is just speculation.

        Liked by 1 person

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