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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

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71 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

    Like

    • 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.

      Like

  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.

      Like

  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

    Like

    • 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/

      Like

      • 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

        Like

      • 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

    Like

    • 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

      Like

      • 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

        Like

    • 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

      Like

      • 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

      Like

  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

    Like

  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

    Like

    • 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.

      Like

  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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