Are the Silica abrasive particles in leather smaller than 0.1 / 0.01 micron?

L

Londinium Armoury

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I am starting to make high end leather strops in small batches for customers, using Grade A veg tan leather on hardwood backing. I made a prototype and sold it to somebody local to me. He then went on to layer it with very fine stropping compound. He told me the results were great. I then said to him I think you should have left it without the compound and just used it as a final honing step after using the fine compound on another surface or cheaper strop. I told him to the best of my knowledge the silicas in the grade A veg tan leather were smaller than his compound, and that putting the compound on actually raised the micron size.
I couldn't be sure if I was 100% correct though, and as these are for future customers I don't want to give them anything but 100% accurate information, was what I told him correct? I have done research on this topic a little bit in the past and as far as I can remember I think what I said was right, but I'd like to be 100% sure before I tell paying customers what to do and what not to do with the strops and give them advice.
Is it better to have a bare strop with grade A veg tan leather as your last honing stage after using compound on another surface, be it another loaded strop, or even wood. What if they are using some ulta fine 0.01 compound, rouge, strop soap etc, is the bare leather silica still finer particle size even than those?
Thanks a lot for the replies in advance.
 
A few years ago I analyzed a variety of strop leathers. Didn't find any silicon in elemental analysis (<0.2ppt). If you look at leather under magnification, you can see that the fibres are around 100nm in diameter. My opinion is that IF there is silica incorporated in the fibres, it's probably in the 10nm range.




veg_horween_06.jpg
 
ToddS said:
A few years ago I analyzed a variety of strop leathers. Didn't find any silicon in elemental analysis (<0.2ppt). If you look at leather under magnification, you can see that the fibres are around 100nm in diameter. My opinion is that IF there is silica incorporated in the fibres, it's probably in the 10nm range.




veg_horween_06.jpg
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1 nm is 0.001 micron right.
So that would make 10 nm 0.01 micron?
Interesting image.
 
You would almost have to burn a sample and suspend it to separate out the silica.
Most silica in the body that is retained is in the form of salts, not oxides.

There will be a much larger concentration of oxides in plant material and some papers, ashes from a regular fire are loaded with the stuff.

IIRC materials as large as 30micron can pass through intestinal wall, that doesn't mean they get incorporated into the skin. IDK...
 
Silica is known to be one of the fundamental components or 'building blocks' of collagen in the skin (ours, and animals' skin as well). It's normally picked up through the diet, in eating plant-based materials which draw silica from the soil. Grazing animals like cattle and horses would then (presumably) incorporate more silica into their bodies (& hides) due to their exclusively plant-based diet. In turn, collagen is a component of the 'connective tissue' in the body, and is what what gives the cartilage, ligaments, skin, hair, nails, etc. strength and durability. No idea what size the 'particles' of silica would be, in skin. But being that it's so fundamental to the skin & body, I have to assume it's always there in some quantity or form.

I've always been of the opinion that for the sake of abrasiveness alone, it's effect in leather, specifically for sharpening knife edges, is minimal and of little significance as compared to other abrasives available for the same purposes. This isn't to say that some forms of leather containing higher percentages of silica (as horsehide is purported to have) can't be better performers, used as strops. But I don't put a lot of faith in leather's real-world impact on sharpening via abrasion, except on a very fine & limited basis.

I've found bare leather to be more useful in alignment of very fine rolled or burred edges, and for 'snagging' and removing weak remnants of burrs along an edge. Works very well for that. And if the silica in leather is part of what makes the leather more durable (and maybe more wear-resistant) via the collagen's effect, that in itself can make a leather strop more durable and useful for maintaining knife edges in the longer run.
 
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Real flax.linen has silicone in the fibers. There is a noticeable bump in sharpness with a straight razor as compared to clean leather.
 
Bill3152 said:
Real flax.linen has silicone in the fibers. There is a noticeable bump in sharpness with a straight razor as compared to clean leather.
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"silicon" or "silica" not "silicone".
"Silicon" is the element. It is found in flax seed.
"Silica" is silicon dioxide, a crystalline compound often used as an abrasive
"silicone" is a synthetic polymer.
 
HeavyHanded said:
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Most silica in the body that is retained is in the form of salts, not oxides.

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I'm not sure what "silica salt" is? Silica is silicon dioxide, SiO2. I think you mean Si(OH)4 or "monomeric silica" which forms silicic acid when dissolved in water.

Obsessed with Edges said:
Silica is known to be one of the fundamental components or 'building blocks' of collagen in the skin (ours, and animals' skin as well). ...
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Do you have a reference for this? As far as I know collagen is just protein (C,O,N,H). Maybe it plays a catalyst role, but isn't incorporated? Outside my expertise.
 
I think silica in leather is most likely incidental due to it being so common in our day-to-day environment and ultimately being rubbed into the leather in the form of dirt/dust. Fresh leather will probably have so little as to be negligible in use.
 
Adding to the 'clear as mud' aspect of a lot of this, there's also the factor of 'sodium silicates' used in leather tanning processes. It may be that most of the noticeable effects of so-called 'silicates' in leather used for stropping may come from that process, instead of from the innate presence in the hide/skin via dietary intake.

https://pubs.rsc.org/en/content/articlehtml/2017/ra/c7ra01160a

In my own earlier post, I referenced 'silica' as being a (possible) component in the formation of collagen in skin, hair, nails, etc. In the effort to try to be a little more correct, it's actually 'silicon' as the element, which seems to get a lot of writeups on the topic of it being a building block for collagen in the body (Googling on 'collagen and silicon', for example).

References to 'silica' in the same context relate to the use of dietary supplements presented in the form of silica. There are some questions around that, suggesting when it's in that form (as silica), it's harder for the body to absorb it for the sake of skin/bone/hair health, etc.
 
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Also relating to leather processing using sodium silicates, I came across this technical document linked below.

https://pubs.rsc.org/en/content/articlehtml/2017/ra/c7ra01160a

There's an interesting comment in the 'Conclusions' section at the end of the document, quoted below (I added the bold/underlined emphasis). Might lend a clue as to how silicates of some form or another end up in the leather, in this case as a precipitated 'coating' of silica particles (or aggregates) on the surface of the leather's microscopic collagen fibers ('fibrils', as described):

"...In summary, the effect of sodium silicates on the collagen structure during leather processing has been investigated by SEM, SAXS and DSC. We speculate that the electrostatic interactions between the positively charged amino groups of collagen with negatively charged silicate species lead to precipitation, forming coatings and aggregates of silica particles on the surface of the collagen fibrils.
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I have no idea how common this process is, using sodium silicates in leather processing. So, I also don't know if it'd impact the leather we commonly use for stropping.
 
When I was analyzing various leathers, I was particularly looking for anything incorporated during the tanning process. I didn't find any impurities; however, I had to remove the fat/oil coating with fairly aggressive solvent cleaning, and that may have also removed any soluble compounds.

There is definitely a problem with the nomenclature of silica being used as synonymous with orthosilicic acid (a single molecule) and silica gel, not to mention being confused with silicates (which are generally too soft to contribute to abrasion).

Although "clean" leather does removal metal, the rate is about 1/1000 of what we see with normally applied 0.25 micron diamond, so it could indeed be due to trace dust incorporation.
 
Another interesting point of discussion here is @wootzblade findings on using a hanging strop vs. a hard backing, as well as improvements in sharpness between cowhide and kangaroo tail leather.
 
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