Loading a Strop

I was going to put a general message..

David Weaver

..about strops and avoiding the things you're talking about (sans carbide fracture - I don't think that's an issue - I think carbides exiting the matrix may be if they aren't well dispersed), and decided not to because it might be dopey..

...I'll go do it, anyway. It is actually true that brand new horse butt can sometimes have enough silica or something else harsh in it to mist the edge of a tool, but it takes little time for it to be worked out. I haven't seen it in anything else other than horse butt (commercial razor strops made of butt strip have some kind of treatment on the surface, but often that needs broken in, too. Mine needed about two weeks' worth of typical razor use to be broken in - the way I did that was something not preferable here, I'm sure, but I used a razor that hadn't yet been conditioned and stropped my razor for use on a broken in strop and then for about 20 seconds or so each day, stropped the unhoned razor on the strop getting broken it. It didn't take that much time.

Most of the action of the strop isn't related to the silica, but rather the bending and pulling off of anything loose. If a burr is so strong that it can't be bent easily, the strop just won't do its job (think rolling a heavy burr with an india stone intentionally without thinning it, just going all to one side and then trying to strop - the leather won't bend it unless you grab on with both hands and do the operation almost vertical - the edge under a microscope is all bent up and horrid even if you can get it off).

I think someone somewhere wrote an article about the silica in horse leather, but it goes to nothing very quickly if there is any and may not have much of an effect if the leather is oiled.

One other side comment..

David Weaver

..if an edge looks good under a small microscope and it's got any flaws, or it's from certain types of steels that don't hold edges well at a given angle, you can actually make it look much worse under the scope by stropping it, though.

What I don't know having said that (because I've seen it under my own scope) is whether or not the bits that break out (a fraction of a thousandth maybe to a thousandth in depth) when stropped would just come off easily, anyway. I think they would.

Re: justify

William Duffield

My are based on David Weaver's photomicrographs of tool edge failures and lack of failure in polished unicorn edges and the reports here of others' successes on unicorned edges. These results, I believe, are based on general metallurgical studies, which can be found by anyone searching the internet for the subject. The easiest information I found resulted from searches for "intergranular steel fracture" and "fatigue crack propagation in metals".

I probably threw you off the scent by using a vague term in my previous post. Sorry. I did not mean to imply that the edge failure was due to scratches within crystals at the edge, but instead those scratches that were located between the edge of a carbide crystal and the adjoining material.

Unicorn uses same abrasive particle

Re: I was going to put a general message..

Bill Tindall, E.Tn.

Unlike a tree that pulls dissolved silica up from the soil and deposits it in the tree, there is no biochemistry that is going to deposit silica in a horses hide. There might be surface contamination, but that would depend on where the horse lived, etc.

Re: I was going to put a general message..

David Weaver

I don't know what the scuffy stuff was on the surface of my butt strip (and not on all of it), but I was concerned at first. It would leave a spiderwebbing pattern on the spine of a razor (which is rolled over at the end of each half stroke). But whatever it was, it's not through and through in the leather. It was also very uniform (not like random particle sizes).

I've heard stories of horses that may contaminate their hides by rubbing in stalls, etc, but I'm guessing that leather wouldn't finish well enough to be sold. I don't know at this point if I could state a preference on leather glued to wood - the wood is so hard that I don't think it matters if its' bovine or horse (the only exception is razor strops - bovine leather doesn't make a very good razor strop, and not much typical shell is found in the US unless someone is importing it from europe or japan. Horween's leather is for shoes and wallets - the surface treatment isn't durable when it's used as a strop (but it feels really nice - not sure if you can even get shells at retail any longer).

not sure...

David Weaver

.once the abrasive on leather is below a certain size, it just doesn't do much to hurt edges.....what i'm not sure about but am speculating on is that the edges are less about a specific abrasive damage and more about an apex angle that's too narrow for the microstructure to hold up.

The oddness in steel that strikes me is that you take two chisels:

1) holds a fine edge wonderfully well. Not really that abrasion resistant. introduce it to something like the junction of brass and rosewood making an infill plane and the results are catastrophic

2) the fine edge is gone almost instantly. very abrasion resistant, but trying to get fine edge holding defect free no matter what is a huge pain (this is chisels, not planing). Then, introduce the same chisel to rosewood and brass on an infill, or even mild steel, and no problem - the edge behind the original apex handles it without issue. But it will not hold the apex.

Really annoying. You can have your cake or eat it, but not both.

Re: not sure...

William Duffield

Heisenberg Uncertainty Principle?

Re: Unicorn uses same abrasive particle

William Duffield

Same size? Same substrate/support? Same speed? Same temperature? Same as what other sharpening abrasive? Or does this imply the same abrasive as was used to grind the primary bevel at 25° in the first step of the Unicorn process? Is everyone using the same particle to get uniform unicorn results?

Again, incorrect premise and justify

Bill Tindall, E.Tn.

The abrasives that are harder and sharper than chrome, and the scratches they leave in the steel, initiate fracturing of the carbide minerals in the steel and thus premature edge failure.

1. Chromium oxide has a higher Vicker hardness than aluminum oxide. So your whole argument for preferring chromium oxide is flawed.

2. The aluminum oxide recommended by us for loading the wheel is the same crystal structure as the aluminum oxide in the green stick. They will leave equivalent scratches. In fact I used green stick on leather early on for Unicorming before I got a buffer.

3. Your rebuttal below to #2 below has little to do with defending the scratch failure theory advanced in your original post.

If you are going to worry people about using green sticks you need to justify your concerns with reliable reference or data. I have seen no evidence there are any concern about "premature edge failure" when using the widely used green sticks.

some of this is probably excusable...

David Weaver

..there have been a lot of false narratives provided with loose abrasives and buffing sticks. Among them:

* chromium oxide is a rounder particle and very gentle, so it will always smooth an edge left by other abrasives (the reality is that hand american chrome ox and others were just closely graded, so when you compare the green stick that was marketed as 0.5 micron for a while to the chrome ox, it looks like the edge made is much smoother. The reality is that if you had 0.5 micron alumina and 0.5 micron chrome ox, the result would be indistinguishable, but closely graded loose alumina isn't widely used for shaving or tool sharpening)

* the diamond myths persist, though there is truth to them in large sizes. At the size that someone would use the diamonds as a finisher (1 micron or below), we've proven that the edge finish wears without visible damage. There's a critical size of some type (2.5 micron loose diamond on a hard surface is poor, 1 micron is great, but at the same time, I have no proof in my experimenting that 2.5 micron is poor because it damages anything, just that the rows are materially too deep. Poor is a relative term - 5 micron is substantially less good than most common finishing stones - 2.5 microns is a little bit better and probably only slightly harsher than most finishing stones ,but it offers no real benefit. 1 micron diamonds and below are great. I see more edge damage off of a black arkansas stone than with 1 micron diamonds

Most of the selling of fine abrasives to the woodworking and shaving communities is done through stores where the vendors are selling hundreds of things. I think they struggle to get accurate information on everything. Forum moderation repeats inaccurate information and you can get banned for challenging it (for example, if you stated that coticule stones could be used with oil, there was a period of time on one of the razor forums that making that statement would get you banned as being false information and stirring the pot).

https://www.pinterest.com/pin/597782550512320913/

(sorry to people who don't have pinterest - I don't - it's just a picture of an old coticule with a label that says "use with water or oil")

Some of the stones that are a bit toothy on water are much more tolerable with oil.

Anyone using a green stick for woodworking can be thankful it's not graded chrome ox unless they have a very specific specialty use - the loosely graded alumina in it makes the stick probably four times as fast. pure chrome ox is very slow if it's 0.3 or 0.5 micron.

I also have a bag of ungraded chrome ox that I tried when hand american stopped selling 0.5. I would guess that it's 3 to 5 microns and unsuitable for finishing.....(the fabled "round and gentle nature" of the particles does nothing to save it - it raises a burr).

Some of this is corroborated with testimonials. It's not uncommon for "professional razor honers" to use green chrome ox 0.5 graded size after 0.25 micron diamond. The testimonial is that the chrome ox is finer because the edge is less harsh after the diamond, but it's more likely that the diamond leaves a finer apex - one that's too sharp for comfortable shaving (because the blade will catch the pore at the back of the hair when lifting the hair . The statement that "things can never be too sharp" is false. If a razor can catch skin behind a lifted hair, the razor is too sharp. chrome ox occupies a range where a razor easily catches hair but isn't quite sharpen enough to catch the back of the pore).

These are things based on my experience. I haven't done a lot of reading of academic papers because they're often hard to grasp in one read and sometimes the topic looks relevant but isn't.

S30V comes to mind to me as something that could help create a lot of OWTs. Cliff Stamp relayed that in order for the fine edge holding to be good with it (this could've been provided by a company to him, or it may be something he tested), the final apex needs to be at least 50 degrees. If the apex is 50 degrees, it won't exhibit early fine edge damage (followed by a long working period of wear resistance just below that). It would be easy for someone who didn't think about possible outcomes to conclude that their abrasive is causing an edge that takes easy damage without finding that all abrasives will lead to the same outcome if an angle is a more typical 30 degrees).

The details of this stuff only gets interesting if someone wants to actually solve a problem, and since the solution isn't interesting (most people will not be satisfied with a 50 degree apex), the problem and various explanations keep their legs.

Thanks for clarification