“Dulling on Glass”


A commonly used technique in honing a straight razor is to begin by dulling or joining the edge by drawing it across the lip of a glass or bottle, or across the edge of a hone.  The purpose being to remove the existing edge and ensure that a completely “new” edge is created with subsequent honing.    The effect is not well understood, primarily since the effect occurs at a scale not resolved by conventional microscopy.  It has been suggested that this edge may be ‘realigned’ by stropping; here we investigate this possibility.

Coti_dulled
Edge “dulled” by drawing across the lip of a glass beaker.
Coti_dulled_stropped
The same edge as above, after stopping on linen. The deformed metal has broken off and burnishing has begun to reshape the edge.
rolled
Razor edge “dulled” by drawing across the lip of a glass beaker. FIB cross-section exposes the profile of the edge.
stropped
The same edge as above, stropped on clean leather. The edge has neither re-aligned nor broken off, instead, the burr has scraped away a layer of leather. The edge is obscured by leather fibers, except where the FIB cross-section has been made to expose the “still dull” edge.

13 responses to ““Dulling on Glass””

      • Really outstanding stuff. I have actually calculated some of these things using gauss’ packed sphere limit and slurry concentration approximations for fun. I kept hitting applicable pressure limits for set angles around 4 micron. I stopped buying stones above this thinking I was just smearing metal around making the bevels pretty. I always just stroped with diamond to finish up. But it looks like the funtion of the edge geometry will hit the minimum convexity of the edge of the material if you were to proceed with progressively smaller micron stones. I would love to see the images of various super/powder metals taken to this limit before overhoning/feathering occurs. I would also love to see what actually happens stropping with compounds after 4 micron bevel setting with various strop densities such as hanging leather, leather on glass, and some sort of fine “lamina like” paper on glass. Im still not convinced there is any advantage to full honing past 4 microns if the material limits nonconvexity at this point.

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  1. I will be presenting the pasted-strop data and discussing “overhoning” in future posts. But you are correct, the data indicate that there is no reason to go beyond 4 micron (Shapton 4k) if you finish with a diamond strop.

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    • Oops! Yeah. I said over honing. After reading a few websites the last few days I am picking up a bit of lingo. I dont want to comment on that.. but if you were interested in some pertinent mathematical stuff, maybe some maple 17 work send me an email. I assume you have it. I would also consider lending various high grit hones if you ever felt like comparing. Once again. Fantastic stuff. Got you bookmarked

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    • Thank you greatly for the quality SEM research. I was so inspired by it, I tried renting a SEM. I am afraid I won’t be able to offer any competition. Nonetheless, the little play time I got has made me appreciate your articles even more.

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  2. HA! I have always thought is was bull to straighten the edge by stropping, it would be interesting to show the effects of a steel. I would suggest that a steel “may” I say may straighten it out if you go edge trailing not leading like most do. But even then I think you now have a weak spot that will either break off or bend back. I believe once you have got damage like that it is best to re-establish the edge. Great work!

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  3. Sir:
    Long time lurker, first time poster.
    I have never been a fan of dulling a razor and have a hard enough time for the prescribed method of removing chips from the edge of a newly purchased antique/vintage razor. I feel, perhaps unjustified, that the loss of blade width and cutting edge is prohibited especially with rare or wide specimens.
    Without disparaging others who have, over the years, gone from one ‘best stone’ to another like the flavor of the week or who berate others on videos that I can no longer watch or subscribe to their technique/philosophy, I am trying to find the best way to test an edge on any given razor with any give stone without reducing or causing damage to the blade, do please bear with me here.
    I have quite a few natural and a couple of high grit manufactured ‘finish’ stones and after a successful bevel set and midrange hone from 5 to 8k I then begin to set about the choice of which to use. My problem in testing is the mentally perceived notion that some of the say coticule is still present on the newly developed shobudani tomae edge or the ouzuku is ‘contaminating’ the hard black Arkansas edge, ect ect.
    So my question is, is there something I should or should not do in testing which ‘stone’ provides the best, comfortable, keenest or closest shave for me?
    On a side note, I must say that you have provided me with the best knowledge of attaining a workable and usable shaving edge without all the background noise of brand, technique or philosophy, and I can’t thank you enough.

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    • There are basically two ways to achieve a “good” razor edge – with fine grit abrasion or with coarser, smooth grit burnishing. Both can achieve a sufficiently keen edge for shaving.
      What is important to understand is that the differences between the various edges that can shave is measured in tens of nanometers, and that is an amount of steel that can be removed or altered with a clean linen/leather strop. In other words, don’t overthink it.

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