Adding Silica To Strops?

[CutterBoi]

I've read in numerous places that leather strops with high silica content at the surface work better than those that don't. I've encountered references on this site to "boning" vegetable tanned cow leather to work the silica from lower fibers up to the surface, as well as references to the superiority of equine shell cordovan arising from its higher silica content. High-silica leather is expensive and / or difficult to obtain.

If silica is so important in a strop, why don't we just work some silica fume / microsilica into our "cheap" leather strops? Or something like West Systems 406 colloidal silica? Or sodium silicate?

 

[Forest Ninja]

.

 

[jeffbird]

A light spray of 1 micron diamond spray works well.

 

[Bill3152]

Flax linen has silica in the fibers. That will definitely kick up a straight razor edge. I've heard many stories about chalk being used on cloth strops. All razor related but I'm sure it is applicable to knives as well. The ease of sprays and compounds is an advantage as you know exactly what size particles you are working with. For razors a sub micron abrasive may be suitable. It may also be for knives depending on what type of edge your looking for.

 

[CutterBoi]

Filter-grade diatomaceous earth supposedly has 60%+ silica content. Problem is that it's probably 3-5 microns, which seems a bit large if one is seeking the finest possible razor edge. Silica fume is far finer, and widely available in smaller quantities as an epoxy filler for not much money.

Sodium silicate (aka water glass) is readily available in solution too. Seems like one could duplicate naturally occurring silica in leather fibers simply by spraying some of this liquid on a piece of leather and letting it dry. I have no idea what the size or hardness the particles left behind on and in the leather would be. Spray enough of the solution on the leather though, you might achieve a thin layer of "water glass" across the entire surface.

Some types of wood can be high in silica content. According to one source, Teak can be up to 1.4% silica. Other candidates include Okoume, Moabi, Movingui.

Asbestos is a fibrous silicate mineral. Strands are up to 0.03 microns in diameter. Maybe we should hone our razors on that stuff; mesothelioma seems like a reasonable price to pay for a good shave!

It seems odd to me that the companies manufacturing strops don't dope their leather with silica so they can claim their product is better at producing a fine edge.

 

[Ourorboros]

Because there are better abbrasives, filtered by size.
Also, depending on what you are doing, you may not want the strop to have it's own abbrasion.

 

[CutterBoi]

Because there are better abbrasives, filtered by size.
Also, depending on what you are doing, you may not want the strop to have it's own abbrasion.

What might someone be doing with a strop where abrasion is not desired? Burnishing?

The more research I do the more it seems to me that strops are almost entirely pointless nowadays.
Leather isn't needed to remove a burr.
Burnishing can be accomplished with things besides leather.
Leather's compressible nature causes it to round off edges while firmer, cheaper substrates (basswood, for example) are far less compressible.
Even the surface texture of top-grain leather seems to me to be sub-optimal for edge work.
And your claim that there are better abrasives available than silicates for producing ultra-fine edges means that naturally-occurring, super-fine silicates in leather are no longer a good justification for leather strops.
The one reasonable use case I see for leather strops is finishing a convex edge.

Maybe my next experiment will be to compare the results of using water glass to the results of using 0.1 micron diamond compound.

 

[Ourorboros]

Chrome oxide and diamond are certainly better abbrasives than silicates, it's not just my opinion. They actually abrade better.
I sometimes use a leather strop to deburr, but I agree that it can be done on the finest stone. In fact, I've seen some say they use their finest stone as a hard strop.
I'm moving to balsa for my loaded strops. I haven't tried MDF yet.

It might be different for the straight edge guys.

 

[Obsessed with Edges]

Sometimes I tend to favor a gentler burnishing action, either with a stone or a strop, when putting finishing touches on an edge. Even though other 'abrasives' would do a better job at actually removing metal and/or polishing, I sometimes want something more subtle than that.

I've refrained from using green compound on simpler steels with the micro-toothy edges I prefer, because even that compound can tend to polish those teeth away pretty fast. So instead, I favor a simple leather belt for stropping those edges, because it does enhance sharpness just a bit and doesn't go too far with a little extra stropping. If the silicates in the leather afford that subtle, magic touch, then so be it.

Point being, I can appreciate experimenting with the (potential) benefits of silicates in / on leather. A certain edge character on a given steel type sometimes 'likes' a certain, gentler, more subtle means of refinement. So, I think there's a niche for that in one's sharpening scheme, depending on preference.

 

[CutterBoi]

Chrome oxide and diamond are certainly better abbrasives than silicates, it's not just my opinion. They actually abrade better.
I sometimes use a leather strop to deburr, but I agree that it can be done on the finest stone. In fact, I've seen some say they use their finest stone as a hard strop.
I'm moving to balsa for my loaded strops. I haven't tried MDF yet.

It might be different for the straight edge guys.

I have no doubt that chromium oxide and diamond are much faster at removing metal than the silicates that may or may not be present in leather. This is just one of those instances where I've encountered some information, made some mental connections, and now want to know why my expectations don't match reality. I see potential for unscrupulous exploitation of the market but I don't see anybody actually doing so.
"Proprietary manufacture process ensure our leather have high silica for better stropping performance and no much money. You pay three times high for same performance strop from other company. Qin Jiao Best Happy Strop work good only $74.99 money back guarantee."

Anyhow, in case you're interested, here are my experiences with regard to using fine sharpening stones for deburring, and wood as a substrate for honing compounds:
Running a knife at a steeper angle down one of my finest stones to remove a burr seems to be detrimental to the final edge.
I am able to use my finest stones without changing angles to minimize burrs to the point of undectability on some of my knives. But some of my knives don't like to give up the burr so easily.
A paint stirring stick from the big orange hardware store, loaded with Sharpal green compound, does an excellent job removing most non-super-steel burrs my finest stones can't seem to remove. I'm fairly certain the stirring stick is pine. I smoothed the surface of the stick with up to 2000 grit sandpaper before applying the compound.
I have strips of basswood loaded with various diamond compounds. Seem to work well. All were smoothed using up to 2000 grit sandpaper except the one on which I loaded 0.1 micron diamond paste; that one was smoothed using up to 10,000 grit sandpaper. (My freehand sharpening skill isn't yet good enough to take full advantage of 0.1 micron diamond paste, by the way.)
I've also tried beech. Worked well, and my favorite so far. But I had only a 5" strip of the stuff, and I've not yet found a source of small quantities at reasonable prices.
No matter what stone or honing strip I end on, I like to try to eliminate any invisible burr on completion by either a couple very light strokes on a plain leather strop or my pants. If the knife is one that was very reluctant to give up its burr on the strops, I'll make absolutely sure the burr is gone by drawing the blade very lightly across a piece of wood.

My finest stones are a DMT Diasharp extra extra fine diamond stone, a Norton Ascent ultra fine ceramic stone, and a Norton Pike J8000 waterstone.

I rank myself as a beginner in freehand sharpening. I've improved dramatically over the past few months and have reached the point of being able to sharpen my knives far beyond what I actually need but I've some distance to go for true proficiency. Hope you don't have high blood pressure, 'cause you need to take the above info with a sack of salt.

 

[garry3]

I've read in numerous places that leather strops with high silica content at the surface work better than those that don't. I've encountered references on this site to "boning" vegetable tanned cow leather to work the silica from lower fibers up to the surface, as well as references to the superiority of equine shell cordovan arising from its higher silica content. High-silica leather is expensive and / or difficult to obtain.

If silica is so important in a strop, why don't we just work some silica fume / microsilica into our "cheap" leather strops? Or something like West Systems 406 colloidal silica? Or sodium silicate?

With the hanging straight razor strops dressing the surface of a strop is done to make it smooth, it was a common way of finishing a leather strop or re-finishing one, most commonly done with a smooth bottle. The superiority of Shell is more a matter of personal preference based on feel that is called draw. Some will prefer a fast draw (smooth slick surface) and others a slow draw and everything in between, the thickness or stiffness of the leather plays a roll also.

In my experience they all take me to about the same place as far as the finished edge is concerned, not that I have tried every leather strop material there is but I have worked with the usual suspects and some not so usual. I have seen no magic in a shell leather strop.

Loading strops has been done for a very long time, usually it is just the linen that is loaded as the leather strops already work as intended. Not every old linen strop will have been loaded with compound though and the ones that are can be found loaded with all manner of compounds including lead or lord knows what. Flax linen isn't so easy to get anymore so I hate to see people add compounds to an old linen strop when a cotton strop would serve just as well.

George Washington's field shaving kit with loaded strops...

User Clip: George Washington's Shaving Kit

Razor, case, and personal items believed to be used by George Washington during the Revolutionary War.

www.c-span.org

 

[CutterBoi]

George Washington's field shaving kit with loaded strops...

That was an informative video clip. Thank you! And thanks for the info about smoothing a strop's surface with a smooth bottle; I'll be giving that a try.

Based on your descriptions, I'd probably prefer a "fast draw"; my fingers like the experience of smoothness, whether that be through direct touch or the tactile feedback of drawing an object across a surface.

 

[CutterBoi]

New info. It turns out the leather industry has done a lot of experimenting with use of silica in the tanning process. It seems silica may be commonly used to prep a hide for hair removal without "pre-tanning." I don't know how much of the introduced silica generally remains in the hide by completion of the full tanning process.

I found an interesting research paper that speaks of creating silica nano particles within the collagen fibers of leather. It sounds as if the goal was to find a cheaper way of tanning hides, but it didn't pan out. It did, however, improve the tensile strength of vegetable-tanned leather by 50%. I failed to understand the mechanism by which this occurred.

APPLICATION OF SILANES IN LEATHER TANNING
J. Benvenuti, S. Griebeler, J. H. Z. Dos Santos and M. Gutterres

https://slub.qucosa.de/api/qucosa%3A34200/attachment/ATT-0/

I'm beginning to think the answer to my question re doping of leather to be used in strops may be that normal leather already has plenty of silicates, and the assertions I encountered elsewhere about cordovan leather being superior because it has more silicates as a result of the amount of plants horses eat may be overstated.

Gotta do the experiments, see if silica / silicates actually do anything good to edges, or if they're too soft to be of much use.

 

[CutterBoi]

My order of sodium silicate solution came in, so I did my first experiment.

I cut a 2"x1" rectangle of full-grain, vegetable-tanned leather.
I rubbed a small amount of purportedly reagent grade, 99.9% pure, sodium silicate 41% solution into the top surface of the leather. The spread was inconsistent, as I took too long to begin spreading the solution and some was already soaking into the leather. So I spread enough solution onto the leather to completely cover the surface in a layer that would override the leather's texture. I let this dry for about an hour. I also poured some solution on the back side of the leather. This was quickly absorbed, and dried quickly.
I then tried smoothing the surface with a piece of 1500-grit sandpaper. The sandpaper clogged VERY quickly. I then tried wet-sanding. The water softened the sodium silicate, made it sticky.
I let the sodium silicate harden again, then tried using 99% isopropyl alcohol instead of water. This did nothing to stop the sandpaper from clogging, but at least the alcohol didn't turn the sodium silicate into a sticky mess.
I did a little sanding, then tried stropping one of my knives on the sodium silicate surface. I didn't have a backing on the leather, so at one point it flexed a little bit, and the sodium silicate surface cracked in several places.
I noted no change in the sharpness of the knife.

I think the sodium silicate solution is a dead-end for the following reasons:
1. Sodium silicate is easily water-soluble.
2. Sodium silicate is quite soft
3. Sodium silicate doesn't appear to be very abrasive.
4. Forming a smooth sodium silicate surface on a strop would be quite difficult because of how quickly sandpaper becomes clogged.
5. A sodium silicate surface is very fragile.
6. If a sodium silicate surface were not created, and instead only enough was applied to the strop to allow a little bit to enter the leather's pores, I suspect the soaked-in sodium silicate wouldn't last very long because of how easily it abrades away.
7. I certainly don't want to breathe the fine powder created by running a blade over sodium silicate.

Next experiment, I'll "bone" some leather and apply a little West Systems colloidal silica, slightly moistened to avoid getting nano-particles of silica dust floating into my lungs. I have higher hopes for this experiment as colloidal silica is silicon dioxide, which is quite a bit harder than sodium silicate.

 

[Obsessed with Edges]

All the other mentioned things aside and offering no opinion there...

Sanding leather is much easier if done with a relatively coarse sandpaper. I've liked using either garnet or aluminum oxide paper at around 100-150 grit or so, of the type generally used for wood sanding. Works very, very quickly in very light passes, with a piece of the paper wrapped around a block. And the coarser grit won't be near as prone to clogging so fast, as will a very fine sandpaper. The leather will be left with a very fine, velvety nap on the surface. And after some use, it'll smooth out to a somewhat shiny surface again.

Also, if the fine sandpaper used was of the silicon carbide (SiC) variety, that friable SiC grit will also break down into very fine dust and shed from the paper easily. If sanding a strop made for use with a very fine compound, the SiC dust can imbed into the fibers of the leather and contaminate the strop surface. That's another reason I prefer using the coarse sandpaper in either garnet or AlOx. It's less prone to shedding from the paper. And if a particle or two of it does come off, it's also very obviously seen and/or felt on the leather and can simply be brushed off without embedding into the fibers of the leather.

 

[jeffbird]

Next experiment, I'll "bone" some leather and apply a little West Systems colloidal silica, slightly moistened to avoid getting nano-particles of silica dust floating into my lungs. I have higher hopes for this experiment as colloidal silica is silicon dioxide, which is quite a bit harder than sodium silicate.

What is the potential advantage of adding silica to a strop rather than the well proven diamond sprays?

 

[CutterBoi]

What is the potential advantage of adding silica to a strop rather than the well proven diamond sprays?

I don't know. Probably none, based on what I'm seeing so far. Before I started researching and experimenting, I wondered if maybe people loved their leather strops because of the polish provided by ultra-fine silica embedded in the leather to their razors. Then research turned up some people saying that some leather works better than others because of higher silica content. And I wondered, if that's the case, why strop manufacturers don't simply add more silica to their strops so they can provide a superior product without a horrifically expensive price. I'm seeing lots of information but none of it is really of a scientific nature, or even a good reality-based nature. Lots of opinions and personal preferences, lots of claims... but no head-to-head comparisons. I'm left with a lot of questions and the likelihood I'll never get the quality of answers I desire. But I can satisfy at least a little bit of my curiosity with not much effort by doing some experiments.

I've learned that sodium silicate is worthless for sharpening. And today I learned that fine silicon dioxide, in the form of West Systems colloidal silica powder, can be successfully used to hone a knife when sprinkled on a smoothed pine paint stirring stick whetted with a few drops of mineral spirits, then worked into the entire surface. I was able to bring the knife I was using for the experiment to the same degree of sharpness I'd achieved using 0.1 micron diamond paste, but no further. I'm at the limit of either the sharpness the blade can attain or my skill. (I wish I knew for certain which...) I plan to repeat the experiment using a blade I've consistently been able to make sharper than this one. Whatever the future holds, I can say that using silica dioxide powder on a wood stick, even when held in place with a bit of mineral spirits, is slow and requires frequent replenishment. I'll be experimenting with silica dioxide on leather too. Maybe the leather will hold onto the silica powder better, and allow the silica powder to sink more deeply, exposing less surface and allowing a finer finish. I'm not hopeful, but I won't know for certain unless I try.

I expect to try using a straight razor for shaving within the next year or two, when I'm reasonably satisfied I'll be able to impart the necessary sharpness to the razor. The results of my experiments now will impact the sharpening equipment I acquire when I'm ready for a straight razor.

 

[jeffbird]

I’ll keep watching your experiments with interest. Diamond spray sure seems like the easy button here.

This thread reminded me to give my razor strop a refresher of 0.25 micron diamond spray. The diamond spray helps the edge go longer before needing to be resharpened on stones.

One side is horsehide and the other is flax. I spray the flax until it is damp and then let it dry. The leather side receives only a fine mist, then it is good for months of use every day.

The razor off of the 0.25 micron is ready to use when it will tree top arm hair 3/8” or more off of skin.

Buy a few cheap razors off ebay to practice with. Highly recommend Tony Miller’s horsehide strops with flax. Buy the beginner strop as you will cut it up starting off. After a while then upgrade if you want. His horsehide strops are wonderful and what I use every day after trying several.

 

[CutterBoi]

Thanks for the info, JeffBird; I appreciate it greatly.

I botched the first attempt at making a strop after I'd finished the multi-hour leather "boning" process. I figured I could speed up drying out the leather by using the microwave to get it warm. I threw the leather in on half-power for 15 seconds thinking it should be safe. Oops... I'm such a dufus. The piece of leather came out of the microwave looking like a steaming piece of crinkled bacon. It was quite hard too. I couldn't flatten it with a rolling pin, so I tried salvaging it by clamping it between two boards in a vice with lots of pressure. That mostly flattened it... but the edges seemed to have a permanent curl. I thought maybe I could just cut the curled edges off. Dang, that leather was significantly more difficult to cut than it had been before! It was so hard to cut with a knife, and I was using so much pressure to do the cutting, that I began to fear I'd slip and give myself a serious injury. Hmmm, what other tool do I have sitting around that can cut stuff? How about a Dremel with a heavy-duty cutoff wheel? Heh, that was fun. The wheel didn't want to cut the leather and, when it did sink a little bit into the leather, the leather put a lot of friction on the wheel, slowing it way down. The wheel did more burning than cutting... and it was all for nothing, because the new edges curled. Oh well, throw a couple hours of work in the trash.

My second attempt at boning leather is slowly air-drying at the moment. I plan to glue it to a board sometime tomorrow.

"Boning" the leather reduced its thickness by about 30%, added stiffness (we'll see just how stiff once the leather has dried completely), and produced a smoother surface. The surface is not as smooth as that of my normal honing paddles. Can leather be made that smooth? I don't know, and I have doubts... It probably doesn't matter all that much though. The leather had a fine "pebbly" type of surface texture before I did anything to it. The new surface is... I don't know. Imagine the original surface, blown up so each little "pebble" is the size of a hill. There's lots of hills, all close together, right? And valleys between each hill. Now imagine that something has smashed the hills down. Each has been converted to a lower, wide plateau. The valleys between all the plateaus have become quite narrow, more like fissures / cracks in the landscape. Shrink it all down back to normal size, and you've got a smooth-feeling surface that a knife edge should slide across without issue, but you can see texture in the leather. I think I've touched leather like this at some point in my life but I don't remember when, where, or what. There's just a vague promise of recollection, a tenuous association, my mind trying to gently pull on a fragile thread to tease an ancient memory free from the rubbish heap of discarded experiences... It's probably something super-obvious.

Anyhow, after I got the leather wet, I worked colloidal silica dioxide into both sides of the leather. The silica seemed to rapidly "dissolve" into the moisture (more likely got whetted out). It started out feeling like a sticky paste but very quickly became slick as I used my fingers to rub it into the surfaces of the leather. The "boning" process should have forced the silica deep into the pores of the leather.

Wear a mask if you try this yourself. Don't do this over carpet. Be careful during cleanup. I wasn't wearing a mask, thinking I could avoid breathing the silica by just holding my breath until I got the silica powder moist. WRONG. Yes, I was able to hold my breath. Yes, the moisture prevented silica dust from floating up from the leather as I worked it in. NO, that was not all the silica! The stuff gets everywhere - on the working surface, clothes, the floor... I managed to breath in a tiny bit of silica dust still floating in the air. Cough cough, now I'm probably going to die of silicosis. Well, probably not. But silicosis is a serious concern.

I predict:
1) This "boned" leather won't round edges so easily as any of the other strops I own, because it will be harder and not have obnoxious knobs springing back up as an edge passes over.
2) Silica dioxide won't provide any advantages over sub-micron diamond spray in my hands
4) I'll end up purchasing a high quality strop when I'm ready for a razor because damn: "boning" even a small 7"x1" strip of leather took a lot of work, and I'm pretty sure I'll never want to touch a "normal" leather strop again after using this "boned" strop I'm making. That horsehide and flax strop is looking mighty attractive!
5) I'll have some sore muscles tomorrow. Maybe a blister.

 

[CutterBoi]

I finished making the strop. Observations of note:

The boned leather is significantly more firm (less compressible) than the leather from which I started as well as all the other strops I own.

The surface is significantly smoother too.

The new strop doesn't round my edges, even with more than a hundred strokes per side on a blade with soft metal. It's a miracle! Every other strop I've tried rounds over my knife edges, noticeably dulling my knives within 20 strokes per side no matter how delicately the edges touch the strops, no matter what angles I attempt to use.

The new strop hones 12C27, 7CR, and some no-name stainless steel (behaves like 420) without addition of any abrasives other than the silica I worked into it during the "boning" process. I mentioned in my prior post that I was experiencing great difficulty in cutting the botched leather strip. The cheap knife I was using needed to be sharpened after that ordeal. I used a DMT DiaSharp extra fine stone to create and remove burrs, producing a mid-grade "arm-hair shaving sharp" edge. I went from there directly to the new strop, skipping several of my usual stages. The strop slowly brought the edge from mid-grade "shaving sharp" to mid-high-grade "hair-popping sharp", which is the limit of my sharpening abilities with this particular knife. I don't know the exact number of strokes required, but it was well over 100 per side. I have no idea whether a standard untreated strop would do the same, as all I've tried round edges long before any significant honing is achieved even when loaded with diamond compounds.

The edge of that cheap knife still has a lot of that feel of "bite" to it that my diamond stones tend to leave. The progression of honing compounds I typically use polishes this bite away before an edge of lower-grade steel reaches this level of sharpness.

My arms are a little sore. Some of the joints in my wrists and hands feel like they're mildly inflamed / irritated. No blisters though. There's got to be a better way to "bone" leather.

That botched strip of leather I spoke of earlier became quite crispy when fully dried. I snapped it into a few pieces just playing with it and, whenever it snapped, it released a small puff of very fine dust into the air. I'll bet this dust was some of the silica I worked into the leather during the boning process.


So...

Does a strop or paddle loaded with silicon dioxide produce a sharper edge than a paddle loaded with sub-micron diamonds? Not in my hands.

How quickly does a strop or paddle loaded with silicon dioxide hone? Very slowly.

Will silicon dioxide hone the edge of a blade containing lots of vanadium carbides? ROFL.

Is silicon dioxide superior to diamonds for honing? No; stick with diamonds, AO, CO, or whatever "normal" abrasive you happen to prefer, because they all work faster.

Is a "boned" leather strop superior to the typical leather strops most everybody sells? In my hands, that's a resounding yes, even when made by someone like me with zero leather-working experience, no idea what they're doing, and little info about the process.

Will I make another? Maybe. I'm giving away the one I just made, as part of a new kit for a niece I'm teaching how to sharpen. I don't want her to have to go through the frustration and wasted hours I've experienced using typical commercial leather strops so I'm making sure she gets a strop that won't round edges so easily. I presently use leather strops only for final burr removal; all honing is done on stones and wood paddles. But a blade sliding across this new strop feels soooo much better to me than on a standard strop that I'm seriously considering spending a few hours to make another, even if it will only be used for deburring. I'm a sucker for the smooth things in life so don't count on the differences being so profound as I'm describing here.

Will I purchase a high-quality strop when I'm ready to shave with a straight razor? Yes; my experiences here, coupled with information I've read elsewhere, lead me to believe the benefits a premium strop offers to the process of maintaining a razor will be sufficient to justify the high cost to me; if I'm going to strop a razor then, by God, I'm going to do it using something that works well and feels good!