Functional Difference in Strop Media

[Jacob Wilson]

I’ve read most of the controversy between burnishing or not burnishing on the various threads here. I’ve always been under the impression that the stiction of leather is enough to pull molecules.

However, I’ve always been at war with myself. Logically, burnishing with leather makes absolutely no sense to me. However, being what I’ve always known about stropping, it isn’t so easy to just switch to the other side of the issue. I still haven’t seen very adequate proof to prove the point either way (although some of Clay’s pictures do seem to show metal that has ‘smeared’ or ‘collapsed’ into itself or it’s valleys). The jury is still out on the matter for me, and in the meantime I feel pulled both ways.

Me too conflicted… But I can tell you one thing… it is not about burnishing, it is physics, you are not smearing molecules, even if burnishing is happening. Even during plastic flow of the surface, there is no way you can smear molecules. To really smear molecules, you need to change their shape. This means changing their geometry. The bonds that hold molecules together give them their physical properties. To smear them you would have to change the molecular shapes, and distort the bonds. Doing that would make them something else. Regardless of whether burnishing steel with leather is possible, you aren’t smearing molecules with your strops.,

Now, I tend to think that we all can agree that stropping works. In the context of this discussion, the real question is why. I contend that it is all due to the abrasives involved. Whether plain leather or charged strops, the abrasives are doing the work. Or so I believe. In no case are we distorting or actually smearing molecules on the atomic scale.

If you have read my other stuff you will know that I am a stickler when it comesto defining terms. I may seem to be a PIA, but I think that the best way to start a meaningful dialog is to make sure everyone is on the same page…

Imagine that…:silly:[/quote]

I can agree with this. I’m no physicist, but what logical side I have (and you’re persuasiveness) sways me.

[Phil Pasteur]

Just keep in mind, I think the jury is out on the burnishing of hardened steel with leather topic.
Smearing of molecules is a quite distinct concept. I have experienced burnishing of soft metals with a hardnened burnishing tools first hand. It works as advertiesed, no question! So that, while I am sure that the smearing and polishing using the plastic flow of burnishing works, I can’t see molecules being smeared as part of the process.

You just need to think smaller to see why.

Phil

[Samuel Gabriel]

When you study the physics of how molecules and atoms work and bind together and move and shift, there are a lot of suprising and amazing things going on.
Like how static electricity and just electricity in general interact with molecules, and how loosely held together some of these molecules are, depending on their structure, and how they interact with each other.
These bonds between molecules are nothing more than electrons shared by atoms.
In some structures, like graphite, the structure is very robust.
In others, molecules can be pushed and moved relatively easily; suprisingly easily in some cases.
When an apple falls off a tree, for example, the molecules in the stem holding the apple lose their electrical bond connections and it falls to the ground. When you touch an object, you are not actually touching atoms or molecules; you are “feeling” the electromagnetic force. This is similar to when you hold two magnets apart with their like-poles facing each other. You feel the magnetic force, which is nothing more than electrons interacting with each other.
When you rub a glass rod with a piece of silk, you are actually rubbing electrons off the glass rod with the silk.
Given some of what I have seen in the world of physics, it does not suprise me at all that the large amount of friction that is created between the surface of the leather and the steel (enough to lift a heavy base off the tabletop) could cause movement at the molecular level on the steel bevel. And when I see the enlarged images, it looks very different to me than the effect I see from mere abrasion.

EDIT: For the record, I didn’t mention “smearing” molecules at any point. That is not burnishing, nor what I was referring to. I am referring to “…the plastic deformation of a surface due to sliding contact with another object. Visually, burnishing smears the texture of a rough surface and makes it shinier. Burnishing may occur on any sliding surface if the contact stress locally exceeds the yield strength of the material…”

[Phil Pasteur]

Great response, and thought provoking. Let me do more research so that I can talk about the steel matrix directly. I think Physists would argue about the surprising part… though I certainly find it amazing.

Keep in mind that the micrographs that showed effects that may be plastic flow were taken at very high magnification. This is what gets people. You are seeing what may be a 10 micon square. If you can pick out only a couple of one micron or less instances in that field of view that “may” suggest plastic flow, what does that tell you about what is going on at the macro level? I would say, on average, very little. I would also point out that a few “dull” micron level abrasive could account for the highly localized effect.

Whenlooking at high magnification photos, the perspective has to be taken into account. It stops being anything that we can relate to directly. Keep that in mind while veiwing them.
Also, the effects that you mention are related to outer electron transfers. Generally these can change the polarity of the outside of a molecule, but the intrisic shape will not change. If it could, that molecule would be intrinsically unstable. I suggest that the iron/carbon/ carbide forming elements in steels do not show this kind of instability. I suggest that though all of the things you mention are valid, they in no way support the idea that we are smearing molecules.

Good talking BTW !!

[Samuel Gabriel]

Yes, a good discussion is always interesting. I suspect that the differing opinions expressed here may simply come down to us coming from differing ideas about the definition of the term “burnishing”. I know in the metalwork world, it very specifically means the technique of rubbing a harder metal on a softer metal to achieve the polishing effect.
But bear in mind that in the wider world in general, the dictionary definition of the term “burnishing” is broader, being simply:
“1. to polish (a surface) by friction.
2. to make smooth and bright”
-or words to that effect.
So we can all agree, I think, that from that definition of “burnishing” we are accomplishing that (to a greater or lesser extent) with leather strops, yes?

[Jacob Wilson]

I think everyone agrees that leather polishes steel. It’s unmistakable. We’ve all experienced it sharpening.

The question is why. Is it because of smearing metal or micro fine abrasions.

[Samuel Gabriel]

I would suggest that it’s a bit of both, as well as mechanically pushing down some of the weaker peaks.

[Blunt Cut]

I am still waiting for some SEM pics from Clay & Sandia to clear up this fuzzy topic. This topic lured me here in the first place – Thanks Anthony Yan 😉

Mean while, just to refresh where my head was… Took 2 box cutter blades. blade1 – stropped on a NEW bare horsebutt leather for 30 strokes at 10 lbs of pressure. Blade2 – stropped on a 7 months USED bare horsebutt leather for 30 @ 10 lbs. Snapped usb microscope 400x for each result. Doh, I didn’t capture a pic for control/untouched blade.

Oh, I remember now. New bare leather won’t do much because a bunch of tiny silicates too small to cause macro (micron level affect). Used leather where contaminated abrasives (dirty fingers :ohmy:)will abrade, while metal particle (from dirty fingers and came off the blade) will burnish. Other physical interactions are interesting but seem unlikely to have major affect in displacing steel matrix – especially high alloy where complex lattices & bonds will certain resist nano-level of molecular displacement/flow.

Just to be obvious – used bare horsebutt leather strop smoothened the bevel. I simple can’t tell how much it burnished but quite sure it did – probably small part by abrasive and major part by swarf.

[Phil Pasteur]

We go back to definitions. If you take the specific definition of burnishing, I think it makes sense to say this is not happening with leather on steel. Blunt cut’s statement about the effects of the leather being due to silicates, means that what he saw was abrasive polishing, not burnishing.

We can polish in many ways. One of them is burnishing, then there are abrasive vapor polishing, chemical and electro-chemical polishing and a few others that I can’t think of right off. The idea that anything that ends up being polished gets that way via burnishing is just incorrect. In other words, just because something is polished does not mean it has been burnished.

I think that it is true that burnished is used as a description of many polished surfaces. While this is true, when using the term to describe a precision process such as sharpening, it should be used precisely!

My contention is simply that when we strop we are polishing by using abrasives. I have seen areas in Clays photos that show exceedingly small features that could be interpretted as being caused by burnishing. These are likely caused by dull or rounded abrasive that pushed the metal arounnd (yes this isburnishing). However the percent surface area in the photos that show this effect is well under (guestimating) 10%. This leads me to believe that the vast majority of the results that we get from stropping is due to abrasion and not burnishing. This follows not only from analysis of the 2000X photos, but from what knowledge I have of physical material properties.

There is one thing that Blunt Cut mentions that does need to be addressed, that is contamination. Given enough metal mixed in your abrasive on a strop, there is more chance to seem some burnishing. In general, I believe that, if your strops are kept reasonably claen and charged with sufficient abrasive, this effect will still be small in comparison to the amount of polishing directly by the abrasive. The other thing that we see quite often is that contamination of the strops leads to large visible scratches, not further polishing. Beyond that, I would think that we agree that strops that are loaded with metal particles (Bunt Cut calls it swarf) become less effective rather than more effective. If we accept that contamination by mtal particles causes some burnishing, the fact that we clean and recharge our strops, and they work better, is pretty good evidence that this is not a positve effect.

[Phil Pasteur]

I think everyone agrees that leather polishes steel. It’s unmistakable. We’ve all experienced it sharpening.

The question is why. Is it because of smearing metal or micro fine abrasions.

Obviously my vote is for microfine abrasion. :ohmy: :woohoo: 👿

This is supported by the vast majority of the photmicrographs that are available. Down to the point that features are below the resolution threshold of the instrument, all we see are scratches. Abrasive polishing sweet and simple! Even at the highst optical magnification possible, the large preponderance of what we see is scratches!

Here is something to consider. When we use a smooth steel on a blade there is not much if any abrasive involved. The process in theory, straightens the edge by bending week sections. I think that it is possible that there is some burnishing going on here as well. Good steels are fairly hard (Rc 63+), the contact area is small, local pressure per area is high.

When we look at micrographs of a steeled edge, it looks nothing at all like a stropped edge. Wouldn’t we see more similarities if the mechanism of the effect was close?

Anyway,
You folks all have a great day!

Phil

[Ken Schwartz]

The nanocloth has no silicates like the leather or even paper contains. These silicates are harder than steel on the Mohs hardness scale, hence they are capable of abrasion.

If you strop on nanocloth with no compound, you get no metal swarf unlike leather – even ‘roo. Even with a light spray of 0.025 poly applied to nanocloth, you will see metal swarf. On leather you see some metal swarf residue, less so on ‘roo but some without the application of any compound. So there is clearly some abrasive component to leather itself. Even fine paper has some level of abrasive, presumably from the wood pulp itself as well as the water particulates involved in paper production. Clairfontaine, a paper mill, owns their own stream and has finer control than most of the abrasive content of their writing paper. Similarly sugar cane based papers seem to have particularly (sorry for the pun) fine surface properties.

At a micro or even nano level, perhaps our definitions fail us and it is best to simply strive to characterize the observations rather than to fit it into preconceived ideas of burnishing or abrasion but rather some hybrid of the two. Clearly the particles are capable of scratching the metal and in so doing both move and push the metal around to some degree. The grooves from the hard particle creating a scratch both remove some metal and push the metal out of the way of the path of the particle. Given the non-spherical shape of silicates – more sheet like, for a given particle size you would expect less depth of cut from a corn flake shape than a bowling ball (sphere) shape. You see this with natural stones too.

So at the lower particle sizes, I think nanocloth ‘rules’ in that it holds more particles more easily and is a bit cheaper than ‘roo but far more consistent than bovine or horse. It’s matrix allows for particles to become entangled more easily and hold their position which would favor abrasion. If the particles roll around, this favors (IMO) burnishing a bit more. At the high end, this becomes interesting in that nanocloth is more of a ‘pure’ play, but ‘roo brings a draw characteristic to the table. Perhaps this draw causes a smearing effect that the nanocloth doesn’t which MAY be advantageous, combining fine abrasion with dragging the surface around a bit too, which may be counterbalanced by the combined abrasion of the fine CBN / Poly particles against the somewhat coarser silicates. Just some theories on how I see it, but what is actually happening would best support or refute my thoughts with some carefully controlled experiments and detailed inspection under an SEM.

FWIW, you can see this rolling around phenomena more readily if you put some 80 micron CBN on Balsa. Some particles roll around pretty freely, some stick out half way in the balsa and stay in place and some get buried in the balsa producing little effect. Think about this next time you are eating a poppy seed bagel as they are of a similar size 🙂 Just don’t get too carried away in a restaurant playing with your bagels 🙂

At these really fine grits, the desired result may not be the same for all. For straight razor users, comfort rules even over sharpness and ‘roo vs nano might go one way and for knife users, perhaps the other way. Time will tell.

Pardon the rambling post, but perhaps it might provide some fodder for discussion.

—
Ken

[Phil Pasteur]

Actually a great post Ken!. Thanks for taking the time to write it!
As I have mentioned many times this will take some objective (SEM) evidence to settle the questions regarding whether what we observe during stropping. Is it abrasion only? Is it actually abrasion and burnishing? What percentage of each type of polishing is in play.

BTW, glad to see you back here.

[Eating Pie]

Actually a great post Ken!. Thanks for taking the time to write it!
As I have mentioned many times this will take some objective (SEM) evidence to settle the questions regarding whether what we observe during stropping. Is it abrasion only? Is it actually abrasion and burnishing? What percentage of each type of polishing is in play.

BTW, glad to see you back here.

When I first looked at Clay’s images of scratches, I saw a mention of contacting Sandia Labs. I believe the post was dated about two years ago. Long enough to make me wonder “so what happened at Sandia?” 🙂 Since all this talk about the SEM remains in future tense, probably a better question is “so what happened with Sandia?”

If there is anyone in this world that comes across as calm, levelheaded and reasonable, it’s Clay. So while I can envision a “get outta here you kook!” if, say I approached them, I just can’t imagine a scenario like that involving Clay. OTOH maybe they didn’t think this was worth giving up precious time on their SEM, or they wanted some math to back it up ahead of time. ??

I’m only asking because there’s always references to a Scanning Electron Microscope in these discussions, but no mention of that actually happening any more.

And now, time for a bagel! B)

-Pie

[Phil Pasteur]

Why not PIE

👿

[wickededge]

The folks at Sandia and I keep trying to connect for our project and the slow down has been on my end. They have a very specific, limited window in which they help companies like mine and it has always come a super busy time for me. I’ll have to wait till the next go round in January to try again. In the meantime, I’ll be preparing my samples so they can do their work.

-Clay

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