What Does Stropping DO ?

Discussion in 'Strops/Stropping' started by Possum, Apr 19, 2011.

  1. Other than some alignment of the metal. What does stropping do? Is it micro plastic flow at the edge? When we know that steel is much harder than plain leather . I realize whats going on when slurry is applied but with out slurry. Possum
  2. Legion

    Legion Moderator Emeritus

    As I understand it, the edge is so fine that just crashing into your hard old beard hairs bends and burrs it. All that happens when you are stropping is, those burrs catch on the surface of the leather, and are then dragged out straight again.

    I'm pretty sure it is no more complicated than that.
  3. It realigns the edge from what I understand. Sort of smooths it out. Microscopically, the edge goes from this: ^^^^^^^^^^^^, to this: --------------
  4. Yep, realigning the edge
  5. Close, but not exactly. If you look at the edge of a razor under a high-powered microscope you see that the edge of the blade actually looks kind of like a saw's edge. That is, a jagged row of teeth that are all aligned. These "teeth" are somewhat smaller than an individual beard hair. When you shave, the beard hair is so strong relative to the edge of the blade that they actually bend / throw the teeth out of alignment, creating an imperfect edge. This damaged edge is still able to cut hair, but if far, far less effective. Stropping on leather (or even your hand if you are stropping a DE blade) straightens the teeth so that your cutting edge is returned.

    After many shave/strops however, stropping alone is not sufficient to repair the edge, so honing is required.
  6. maxman

    maxman Moderator Emeritus

    Very much the same reason a Chef will use a steel to realign their knives before they use them.
    It doesn't replace honing, nor does it actually sharpen the blade for any more than a few applications.
    You have to strop a blade before every use until it becomes ineffective. Then it's time to hone.

    I have recently got into stropping my kitchen knives and pocket knives on my old filly stop. It makes a big difference for a while, then it's time to do it again. I wouldn't use my good strops though.
  7. Ah thank you for the correction, it seems that I was slightly off. I was under the impression that even though the edge was slightly jagged, but the stropping made it much more linear. So is it still saw toothed, but simply less so?
  8. Thanks guys for the info.. Possum
  9. Lots of misinformation in this thread.

    There are photos on these forums and elsewhere of razor edges at 800 - 10,000x magnification (electron microscope) that somehow fail to detect teeth in the edge of a properly honed razor. Low grit hones do leave a sawtooth edge, which is useful for knives but inapplicable to razors. At high resolution the edge of a properly honed razor looks like it's torn off - the steel is too thin to hold together under the tug of the hone, and rips off. A razor with a sawtooth edge has not spent enough time on the intermediate hones to remove the coarse scratches, which means that those intermediate and fine grit hones are only honing the high spots on the edge.

    As for stropping, there is some evidence that the strop cleans off corrosion and removes oxidized steel. I've not seen any evidence that it aligns the edge. This is often claimed about strops based on a comparison to knife steels, but a leather/canvas strop is not made of steel and the comparison is inapt.

    http://blog.modernmechanix.com/2008/06/02/wonder-photos-reveal-unsuspected-facts-about-razor-blades-and-shaving/ - 1937 article and optical photos of razor edges, showing what edges look like after use, and the effects of stropping a used edge.

    http://www.mse.iastate.edu/fileadmin/www.mse.iastate.edu/static/files/verhoeven/KnifeShExps.pdf - paper by a Professor of Materials Science (he's a metallurgist) at Iowa State, on various aspects of honing. Not specifically about razors, but includes high-res shots of commercial razors and hand-honed straights. Also examines stropping, and found no evidence that it straightened the edges.

    One caveat about the Verhoeven paper is that his methodology changes between chapters, so you can't compare results between chapters. e.g. You can't infer from his data that 0.5 micron diamond is better than 0.5 micron chrome oxide, because they were obtained in different chapters and were used differently.
    Last edited: Apr 20, 2011
  10. Of the papers I've read from Dr. Verhoeven's studies the stropping was done on a spinning leather wheel and compared a loaded chromium wheel to plain leather. Thus, showing the plain leather added no refinement to the edge but the loaded wheel did. Thanks, Possum
    Last edited: Apr 20, 2011
  11. I'm glad you got to this and corrected the misinformation. I believe we also concluded that the linen strop does effect a mild honing when done properly and enough. Good stuff and thank you, Mr. Parker.

  12. While Dr. Verhoeven's labratory findings are good, there is still much real world evidence that stropping on plain leather improves an edge to the point of realizing a decent shave. Theres just no denying this. How this actually is brought about I think we're hitting at some of it here. Possum

  13. ~~~I'm a fairly new straight razor shaver (since early March). I too have been under the impression that running my razor's edge back and forth over the leather component somehow re-align's the edge. Now how I came to believe this is not important other than that it is probably been considered empirical to many, but I'm not here to debate that. I am respectfully asking why it's considered important to strop on a smooth surface and not on one that has an interrupted surface...surface interuptions like knicks in the leather stropping surface. Most anecdotes say to fill in strop nicks (if large enough) with a glue (CA?, what does CA stand for anyway?) because if the surface is left with an interuption, that interuption can transfer to the razors edge? Remember...I'm just asking but if we don't want our razor's edge to touch a divit caused by a nick, then there must be some association with that divit and edge mis-alignment?


    Reddick Fla.
  14. I hope there are some experts who have real scientific evidence about stropping. I don't. The empirical evidence is obvious. Stropping works. Shaving edges are more effective after stropping. Why? Who knows?

    There are many theories and stories about little steel fibers aligned with this or that. Some actually say that after stropping the little jagged bits "grow" in the direction of the stropping. My experience is that people who talk about invisible things tend to make stuff up. Pictures, or it did not happen. If the experience of many is that shaving edges get better after stropping on plain leather, then go with that. Science can catch up eventually.
  15. No, he used flat leather strops for his stropping test. He also used strops loaded with diamond and chrome oxide, but those were in different chapters.

    His plain leather stropping test wasn't specifically looking at aligning the edge, but rather removing the burr that was visible at 10,000x magnification. He found that the unpasted leather was unable to straighten out the burr. Pasted leather (both diamond and chrome oxide) did remove the burrs as detailed in previous chapters in his study, but plain leather had no observable effect. If leather is unable to affect the extremely thin burrs then it seems unlikely to affect the much thicker steel of the edge itself.

    Verhoeven did not study the effect of linen on an edge, nor did he study used and corroded edges. The article on the Modern Mechanix site did find that stropping removed corrosion and their photos taken under a high-magnification optical microscope (~3000x, reduced to ~2000x by the time the photos had been resized for publication) seemed to indicate that the stropping did sharpen the damaged edge. Unfortunately that article didn't give any details about their strop.

  16. Linen is an interrupted surface, and is an important component to stropping. One of my favorite strops has a very coarse corrugated linen.

    If you get a nick in your strop just cut away any flaps left hanging, and sand it down around the edges of the nick to smooth out the transition.

    It isn't the divot in the leather that causes a problem, it's the edge of the nick that's the troublemaker. Leather tends to swell with humidity, and bathrooms tend to be humid places. The leather at the edge of the nick is exposed to the humid air on two sides whereas the rest of the strop is only exposed at one side, so the leather around the edge of the nick will swell more causing it stick up above the surface of the strop just a bit. The edge will bang against this as it goes over the strop, and has a minor negative effect on the edge. Sanding the edge of the nick to round it off a bit prevents this from happening.

    I would not fill it in with CA (= cyanoacrylate = super glue). I have never heard of this recommendation myself, and it sounds like a good way to ruin a strop. CA will penetrate the leather and produce a hard spot on the strop which will not flex with the rest of the strop, so in effect it will also be a high spot on the strop, but even worse it will be a hard high spot.
  17. I agree that it does *something*, but I don't know what that is anymore. I always assumed that the leather aligned the edge, but this doesn't show up under magnification. So I don't know what the leather is doing, except it's important.

    Linen is another matter. Linen definitely seems to act like a mild hone. I've been able to take razors that were no longer sharp and return them to shave readiness just by stropping them (many many times) on unpasted linen. The problem is that linen seems to leave the edge feeling rough, so you have to use the leather before trying to shave with it. Though some people prefer to shave directly off the linen, so YMMV.
  18. Mr. Parker, Read exactly what I wrote, I'll quote it again for you: "Of the paper I've read..." I was not saying 'your' paper. I was meaning this paper;
    Where he examples several types of leather wheels for stropping and the more common stationary type. All the accompaning photos show how little affects the plain leather had on the steel. While the loaded strop had much affect at refinement and burr removal. (different slurries used) Alfred Pendray
    an accomplished Master Bladesmith did the stropping on the running leather wheels. (around pg.29) We maybe closer than you think... I'm just saying plain leather has 'some' affects. We already agree a loaded strop has much more affect on the steel. While some of Dr. Verhoeven's findings strike against, shavers normal pratices its hard to argue with a camera. So, load them strops up boys we're going to do some shaving! Possum
  19. Take your fingers, weave them (This is the church...) together. Now straighten them out so they look like an old-style dish rack (viewing straight on at your thumbs/forefingers).

    This is what a honed edge looks like (albeit not uniformly), a bit exaggerated, but you get the idea.

    Now move your fingernails towards each other all at once along the axis (that this is possible on) perpendicular to your line of vision (assuming you are holding your hands so that your thumbs are near your eyes and your hands extend directly away from your eyes). Now your hands should be similarly held to the classic prayer posture (Think praying Cherub ornaments at Christmas), but with the fingertips still alternating so it's pointer, pointer, middle, middle, ring, ring, etc.

    This is what an edge looks like after being taken to a honing/sharpening steel or a strop.

    Using the edge returns it "mostly" to the dishwasher rack shape (but less uniformly, though it wasn't uniform to begin with, it's just much harder to visualize if we introduce that, so one side will be more heavily populated with metal bits). But because of metal fatigue, it also will have some of those bits break away. More and more will break away each time you use and steel/strop the edge. This is why even if you don't damage the edge, eventually it will still need to have the cutting edge reshaped via honing (or abrasive stropping). When enough break away that you find the cutting ability or shaving ability noticeably degraded, then you touch up the razor or sharpen the knife or tool.

    Oh and Mparker, they aren't teeth in that way we visualize them, they are just functionally like them. As you said, the edge is torn away. However, if you were to make a topographical map of the edge with the zero plane being the hypothetical "ideal" high point of the bevel (on either side). When you hone the opposite side of the bevel, and metal is abraded away, what you might call "odd" metal is pushed up into your plane (the bevel not contacting the hone) becoming topography. Now since metal isn't fluid at the temperatures we're at, this obviously isn't going to act is if it were cast steel... so the strop doesn't need to abrade it. It contacts the plane (bevel) at a structurally weak point. So we strop to gently push it back in line, avoiding ripping it off and degrading the edge. That's the "teeth". Not just gouges with perfect little plowlines between them as low grit bevel scratch patterns make some people visualize. Fortunately, for the sake of realigning these "teeth", it doesn't matter how you visualize it. What matters is that they are connected to the blade by fatigued steel and can be pushed back into alignment.
    Last edited: Apr 23, 2011

  20. ~~~Okay, all of that makes sense, and now I know what CA glue is (superglue) Off to do some strop trimming and sanding...


    Reddick Fla.
    n00b strop beater=:)

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