“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.

  10 comments for ““Dulling on Glass”

  1. November 18, 2014 at 3:47 am

    Your blog is great. Would you be able to do an article on edge sharpness after breaking burrs off vs. removal by grinding?

    Like

    • November 18, 2014 at 3:22 pm

      Thank-you. I do have some observations and images related to burrs and foil edges that I will present in the future.
      Todd.

      Like

      • cris
        December 7, 2014 at 10:30 pm

        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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  2. December 8, 2014 at 8:18 pm

    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.

    Like

    • cris
      December 10, 2014 at 1:40 am

      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

      Like

  3. Dr. Matt
    December 28, 2015 at 12:56 am

    Have you ever looked at the edge after dulling on the edge of the stone ?

    Like

    • December 28, 2015 at 7:37 am

      Yes, many times. The apex is usually abraded rather than folded. Typically, with light force on a fine stone the apex is flat with a width of approximately one micron.

      Like

  4. mtknivesnet
    March 6, 2016 at 7:22 pm

    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!

    Like

  5. December 30, 2016 at 8:52 pm

    I’m not quite sure what is the implication here. Do you suggest one should dull their edge before going about your suggested method (Simple Straight Razor Honing)?

    Like

    • December 30, 2016 at 9:35 pm

      I don’t personally do this. It is really just part of a method for confirming that you have created a new apex.

      Like

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