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Is polishing compound necessary on a leather strop?

Discussion in 'Maintenance, Tinkering & Embellishment' started by sogflash, Nov 16, 2012.

  1. sogflash


    Aug 28, 2011
    Is polishing compound necessary on a leather strop?
  2. Depends on what you hope to achieve with the strop. If you're just looking to clean up some light burrs from your edge, or gently re-align a rolled wire edge, a bare strop can work just fine. If your goal is to further refine, hone and/or polish the bevels, some compound would be a good idea. All of this depends on the edge being ready for stropping, too. If the edge isn't very sharp to begin with, or not fully apexed, a strop of any configuration probably won't help too much, with compound or not. Most of the real work needs to be done on the stones first, and stropping shouldn't take more than maybe 10-20 passes (or less) to really make the final edge 'pop'.
    Last edited: Nov 16, 2012
  3. sogflash


    Aug 28, 2011
    Are there any brands of polishing compound out there you can recommend?

    I need something to use after I have sharpened my knives, and I want to use it just to keep the edge sharp for longer periods.
  4. A lot of people here like to use diamond and/or chromium oxide (green) compounds, usually at ~1 micron sizes or smaller (green is usually ~0.5 micron on average). DMT and HA (HandAmerican) are very popular for the diamond compounds, and HA also has a good rep with their green compound. The green is widely available from many sources, and is usually found in 'stick' or bar form, but some vendors also have it in powdered or liquid-suspension form (HA).

    Paste polishing compounds using aluminum oxide abrasive, like Flitz or Simichrome, also work well.

    A lot depends on what steels are being stropped. More abrasion-resistant steels like S30V, D2, etc., will respond better to diamond compounds. The green compounds work very well with simpler steels like 1095 and other basic carbon steels, and many of the mid-range stainless steels like 420HC/440-series/AUS-8/etc. I've found Simichrome works pretty well with all but the most abrasion-resistant steels. Haven't used Flitz yet, but many here have, and I think it would perform very similarly to the Simichrome.

    More often than not, I'll use either the green compound or 1 micron diamond. Those handle virtually all of my blades well. I tinker with others occasionally, but always fall back on the green and the diamond.
  5. matt1987


    Nov 2, 2009
    I was doing a little research on strop paste last night. It seems plain ol' toothpaste works in a pinch. Someone also suggested making a toothpaste and baking soda mixture. I may try it out tonight on an old belt before I use it on my good strop.
  6. Some toothpastes have what's known as 'hydrated silica' in them, which is sometimes (but not always) hard enough to abrade hardened knife steel. But, it's still not very hard, and likely won't do much on many blades, aside from lightly burnishing or 'cleaning' the surface. The natural silicates in a bare leather strop accomplish more or less the same thing. An easy way to test how toothpaste or any other compound might work on steel is to put some on a piece of clean, white paper and 'strop' on the paper. If the compound is hard enough to abrade (polish) steel, the steel removed will be left in black/grey streaks on the paper.

    Baking soda (sodium bicarbonate) is much, much softer than the silica in toothpaste, at ~2.5 on the Moh's scale of relative hardness, compared to Moh's 5-7 for most common knife steels (hydrated silica is around ~5.5-6.5). It might serve to clean foreign debris from a knife blade, but won't do much for abrading or polishing by steel removal. Baking soda does work well for scrubbing the heavy/flaky rust off a neglected blade though. It also will help neutralize acids that cause rust, and is useful for cleaning up a carbon steel blade after a 'forced' patina using vinegar or some other acid, both for removing the rust created and for stopping the acidic reaction on the steel.

    Chromium oxide (green Cr[SUB]2[/SUB]O[SUB]3[/SUB]) is ~8-8.5 on the Moh's scale, aluminum oxide (Flitz/Simichrome) is usually above ~9 or so, silicon carbide (in many 'black' compounds) is higher at ~9.5 and diamond is the hardest (10).
    Last edited: Nov 16, 2012
  7. stitchawl


    Jul 26, 2008
    With respect, I have to clarify a point you made here...
    A 'bare' strop still hones and polishes an edge. It just does it at a much finer grit size than when some other compound is applied. Most people are using Chromiun Oxide (.5mic) as their 'finishing' compound. Those wishing to go further use a diamond compound at .25mic. A bare leather strop's natural silicates are around .05mic and smaller, which is why it gives such a sharp finished product. BUT.... you really won't get the full benefits of that unless you already have worked down to a proper starting point before going to the bare strop. Without taking the edge down first, yes... a bare strop will function to clean up some light burrs from your edge, or gently re-align a rolled wire edge, and will do it very well, as will denim, your palm, or your shirt sleeve. But if you progress down through the grit sizes and THEN go to the bare leather strop, you will see a major difference very quickly. It will produce an unbelievable edge!

  8. bluntcut

    bluntcut KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Apr 28, 2012
    Here is a recent interesting BF thread on bare leather stropping. Jump right in :cool:
  9. I know this. It just does it much, much more slowly, and at a degree that'll only be noticeable if the edge is already pretty refined. And even slower with steels that might be more abrasion-resistant than what the silicates in the leather can polish/abrade effectively. That's the point I was emphasizing in my post. Whether a compound is 'necessary' becomes glaringly important if the edge isn't ready for bare-leather stropping, which is where something more aggressive will help.
    Last edited: Nov 16, 2012
  10. Magnaminous_G


    Jul 13, 2011
    All the more reason to practice stone work and get the edge as refined as possible coming off of the stones, in my opinion. Improving my stone work and getting results on bare leather has been a huge sharpening revelation for me.
  11. As echoed in my earlier comments (post #2):
  12. Lagrangian


    Jun 25, 2011
    Hi stitchawl,

    Is there a reference where I can read about the size of silicates in leather? This is pretty interesting! I would love to read up on how it was measured.

    Some stropping compounds go down to 0.025 microns.

    btw, the resolution of optical microscopes only go down to about 0.2 microns, so to measure or see anything smaller one would need something like a scanning electron microscope (SEM), or other fancy stuff (like a scanning-tunneling-electron-microscope (STEM), or atomic force microscope (AFM), etc.).


  13. stitchawl


    Jul 26, 2008
    Eggs-actly! I keep referring back to our friend, the neighborhood barber. We never see him use compounds, nor do we see him use stones. His stone work is all done long before the customer comes in for a shave. Then just just gives his razor a dozen strokes on a bare leather strop and goes to work! That customer will come back again and again because the barber's razor was sharp enough to give a comfortable shave. The silicates in his horsehide strop gave his edge that extra little touch-up to make the shave easier on the skin!

    I'm really bad at saving links to references. I figure that if I can find 'em once, I can find 'em again. That said, I don't think I've EVER found a desired link a second time when I needed it...

    That's some mighty interesting compound you've linked to. I've never seen anything that fine before. In general knife-land, I've seen diamond spray down to .25mic, and in the razor-country, there is Thiers-Issard paste, Dovo Red and Dovo Black, and a few others that are marketed to straight-razor folks. Personally, I go from .5mic Chromium Oxide right to a horsehide bare leather strop and that gives me the results I like. The natural silicates in leather are reported to be sized from 0.1 down to 0.01. (Whether these reports are accurate or not is anyone's guess.) But, if correct, the horsehide strop is taking me down to about the same level as the $60-a-bottle stuff in your link, and it never runs out... :)

  14. Lagrangian


    Jun 25, 2011
    Hi Stitchawl,

    If you can find a reference for the size of silicates in leather, that would be awesome, and I will add it to my list of "Length Scales for Sharpening."


    P.S. Here's my list of length scales for sharpening (which I've posted before):
    The two most important lengths are 0.4 microns (sharpness of a razor blade) and 0.2 microns (resolution limit of optical microscopes):

    180 - 7 Microns: Diameter of human hair. https://en.wikipedia.org/wiki/Hair
    100 Microns: Approximate thickness of paper (copier paper of weight 24 lbs; 500 sheets is about 2 inches thick).
    16 Microns: Thickness of household aluminum foil. http://en.wikipedia.org/wiki/Aluminum_foil
    25.4 Microns: = 0.001 inches (1.0 mil). Standard resolution for an imperial caliper.
    2.54 Microns: = 0.0001 inches (0.1 mil). Standard resolution for an imperial micrometer.
    0.75 - 0.38 Microns: Wavelength of visible light. http://en.wikipedia.org/wiki/Visible_light
    0.4 Microns: Sharpness of a modern razor blade. http://www-archive.mse.iastate.edu/...te.edu/static/files/verhoeven/KnifeShExps.pdf
    0.2 Microns: Resolution limit of optical microscopes. http://www.microscopyu.com/articles/optics/objectiveproperties.html
    0.05 Microns: Sharpness of diamond coated razor blades. http://www.technologyreview.com/computing/25988/
    0.005 Microns: Sharpness of a diamond microtome knife. http://www.tedpella.com/diamond_html/diamondk.htm
    0.003 Microns: Sharpness of concoidally fractured obsidian. http://en.wikipedia.org/wiki/Obsidian
    0.003 microns: Distance between a hard drive head and the spinning platter. http://en.wikipedia.org/wiki/Disk_read-and-write_head
    0.00034 Microns: Van Der Waals diameter of a single carbon atom. http://en.wikipedia.org/wiki/Van_Der_Waals_Radius

    The needles used in scanning-tunnelling-electron-microscopes (STEM) and atomic-force-microscopes (AFM) are so sharp they literally have a single atom at their tips.
    Also, x-ray telescope mirrors are atomically smooth. http://www.mpe.mpg.de/xray/wave/technologies/mirror.php

    This is also fairly interesting when combined with Komitadjie's Grand Unified Grit Chart, which is an approximate conversion between sharpening stone grits and microns. The graph below is made by Mr. Wizard who used the data compiled by Komitadjie.
    Last edited: Nov 17, 2012
  15. Lagrangian


    Jun 25, 2011
    Well, maybe? :) I don't have that much experience with stropping, and I don't have any fancy microscopes, so I don't know. But _in theory_ one might wonder:
    (1) Do the diamond abrasive would work much faster than silicate particles? (Verhoeven's results suggest that plain leather has relatively little effect, but that's for his technique and leather.)
    (2) Do the silicate particles eventually wear out (ie: break down too much and/or the particles become too smooth)? What is the hardness of silica particles versus modern knife steels?
    (3) Are silicates just below the leather surface able to migrate to the surface? (Maybe the mechanical compression/decomperssion during stropping allows migration of silicates?)

    btw, having the abrasive break down is not necessarily bad; most metal polishes are designed to have friable abrasives (from what I've heard) so that as you keep polishing, the compound gets finer and finer. Also having smooth abrasive particles is not necessarily bad either, depending on what kind of abrasion you want (ie: maybe the smoother particles would have some burnishing effects).

    The above is just speculation on my part, so could be hogwash.
    It would be nice to see some real experiments and/or hear more from people's experiences.

  16. Diamond would always work faster, for a given particle size. Comparing diamond to silica (and there are many types of silica), there's still a vast difference in hardness, and maybe also a difference in particle/crystal shape, which greatly influences how 'fast' or aggressive the particle will cut/abrade/polish. Diamond & silicon carbide, in particular, are usually known for their more 'jagged' shape, sort of like broken glass. Other abrasives might be more 'blocky' or roundish in shape, and therefore may not cut as aggressively. So, even if the diamond and silica particles are of relatively similar size, there'd still have to be a big difference in how each works.

    I'm curious also, about finding the 'scoop' on natural silicates in leather. In very vague terms, I think it comes down to how the natural silicates in the earth's crust (many or most from remains of ancient sea organisms) are absorbed/metabolized into plant matter (cell walls), then the plant matter is consumed by grazing animals (cattle, horses), and the natural silica is then metabolized/absorbed into the connective tissue of the animals' skin. The size of the silicates, I'd assume, would therefore be limited by the thickness of the plant cell walls into which they were absorbed or metabolized. This is what I think I understand from what I've read, but I've still never found anything that definitively describes how it happens from point 'A' (origin of the silicates) to point 'Z' (where it ends up on/in our leather strops). Assuming this is actually what happens (and I really don't know), then geology, zoology, botany, biology, chemistry all seem to play into it, which is pretty darn cool. :)
    Last edited: Nov 17, 2012
  17. Lagrangian


    Jun 25, 2011
    I know almost nothing about tanning... But apparently some silicates (specifically sodium silicate) are used in tanning?

    I'm not super strong in chemistry, but here's what I understand:
    Silica = SiO2 (silicon dioxide), one of the primary ingredients in glass making, fused quarts, etc., and primary component of sand. My understanding is that SiO2 is covalent and not ionic.
    Silicate = Ionic compounds containing SiO4 with a charge of minus 4, and other similar variants.

    "Silica, or silicon dioxide, SiO2, is sometimes considered a silicate, although it is the special case with no negative charge and no need for counter-ions. Silica is found in nature as the mineral quartz, and its polymorphs."--wikipedia

  18. There's also something called 'biogenic silica' (BSi), which is also known as 'hydrated silica' (mentioned in my earlier post about toothpaste). Here's an interesting passage from Wiki on the subject (bold highlight added by me):

    Regarding 'leaf phytoliths':
    and about cell walls:
    Still don't know if any of this relates to the 'silicates' we presume to have in our leather strops (horses/cattle eat, digest and metabolize grasses containing silica). But, who knows? The quest for knowledge continues... ;)
  19. stitchawl


    Jul 26, 2008
    Yes, but at that microscopic level, is speed really an issue? Is taking 11 strokes on a strop effectively faster than taking 12? Faster, sure. But when all is said and done, has it saved enough time for a cup of coffee?

    Break down... yes. But not to a rounded state. Fractured would be a better discription, exposing fresh edges with which to cut. The silicates are harder than 'most' modern steels, and certainly much harder than traditional carbon steels.

    Absolutely! That was the whole reason for the "Russian Leather" tanning process, and why rolling, compressing, and casing new veg-tanned hides make them more effective for bare leather stropping.

    My reading is the same, as is my take on it as well.

    Silicates are the single most abundant chemical on our (or, at least my) planet. They are found in every carbon based life form, and found mixed into most of the non-living structures as well. Our own skin has plenty of silicates in it, which is why, when one takes a well honed edge and strops it on one's palm, the edge gets sharper. We see our friend the barber do this often. This leads me to think that perhaps stropping on a vegetarian's skin would work better than on a carnivore's hide. I shall now go in search of a Virgin Vegetarian's Thigh... purely for research purposes...

    I think it's important, though, that in our reading, we keep in mind that not everything we read on the Internet is accurate, and that we temper our beliefs with some rationality. Perhaps there are no more virgins...

  20. bluntcut

    bluntcut KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Apr 28, 2012
    For a quick test, I burned 1mm top layer (smooth side) of a 4x10cm horsebutt leather. Put ash on a packaging tape covered glass block - changed substrate from connective tissue to plastic and silicates concentration. Strop my endura4 vg-10 dry-shave edge at 45* affecting the heel half. After ~600 strokes per side, the whole knife still dry-shave afterward and I didn't see a micro-bevel nor rounding using my 400x usb microscrope.

    For comparative, I use 0.1micron diamond paste and stropped 100 strokes 45*/side. Afterward, edge of my endura on the heel part is rounded, it won't shave nor push cut newsprint.

    2cents tests -> just for fun -> prove/dis-prove nothing.

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