Why The Problem With Leather Strops???

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NorCalQ

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Dec 13, 2018
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I sharpen on TSProf K03/Kadet. When I get down to stropping I use cow leather, kangaroo and balsa with WE diamond paste or Gunny Juice Diamond Sprays. Every time I use leather or kangaroo, I get micro scratches on clean bevel, however when I use balsa, I get no micro scratches. Why? This happens with no added abrasive as well.
 
Few reasons. Dirty strop or you’re polishing the edge and exposing scratches or you’re applying more pressure when using the leather and creating scratches. The diamond spary is an abrasive.
 
So I considered the exposing of existing scratches, however when I get down to 5u without any apparent scratches using a magnifier other than those expected from the abrasive, then moving to 3.5u and suddenly seeing them, lead me to believe they came from the current strop. Am I wrong on this? I've gone 'round in circles going back to stones to rid the scratches, only having them reappear during stropping. Is this a common problem? All that said, when I switch to balsa strops, everything is ok. I'm really trying to use the roo strops, as everyone seems to have good results from them.
 
115Italian said:
Few reasons. Dirty strop or you’re polishing the edge and exposing scratches or you’re applying more pressure when using the leather and creating scratches. The diamond spary is an abrasive.
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I'm wondering too, if it's not just the fact that you're polishing the edge a bit more, making it easier to see existing scratches. I'd also make sure your leather isn't peeling up around the edges. I've gone to balsa myself.
 
NorCalQ said:
I sharpen on TSProf K03/Kadet. When I get down to stropping I use cow leather, kangaroo and balsa with WE diamond paste or Gunny Juice Diamond Sprays. Every time I use leather or kangaroo, I get micro scratches on clean bevel, however when I use balsa, I get no micro scratches. Why? This happens with no added abrasive as well.
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I'm inclined to believe the processing & tanning of leather is an inherently dirty process and therefore prone to leaving the finished leather with relatively coarse contaminants of dirt, sand, etc. On the other hand, a simple piece of balsa or other wood should remain relatively clean after the simple process of cutting it or smoothing it to make it suitable for stropping. This might be one reason you're not seeing the same micro-scratches with the balsa that you're seeing on the leather strops.

And secondarily, I'd expect ~3-micron diamond compound to produce a decent mirror as seen by naked eye, but not necessarily as seen under magnification. This is what I've come to see and expect in using DMT's 3-micron compound, anyway, which is one of my favorites for decent polishing. More specifically, that ~3-micron threshold seems to be where the finish transitions from hazy to what appears as a mirror by naked eye. I've used it on wood strops of either balsa or basswood. I wouldn't really expect to see (by magnification) a scratch-free mirror at 3 microns, or anything coarser than that. If expecting a finer, more perfect mirror, you'd probably need to take the progression below 1 micron at least.
 
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Obsessed with Edges said:
I'm inclined to believe the processing & tanning of leather is an inherently dirty process and therefore prone to leaving the finished leather with relatively coarse contaminants of dirt, sand, etc. On the other hand, a simple piece of balsa or other wood should remain relatively clean after the simple process of cutting it or smoothing it to make it suitable for stropping. This might be one reason you're not seeing the same micro-scratches with the balsa that you're seeing on the leather strops.

And secondarily, I'd expect ~3-micron diamond compound to produce a decent mirror as seen by naked eye, but not necessarily as seen under magnification. This is what I've come to see and expect in using DMT's 3-micron compound, anyway, which is one of my favorites for decent polishing. More specifically, that ~3-micron threshold seems to be where the finish transitions from hazy to what appears as a mirror by naked eye. I've used it on wood strops of either balsa or basswood. I wouldn't really expect to see (by magnification) a scratch-free mirror at 3 microns, or anything coarser than that. If expecting a finer, more perfect mirror, you'd probably need to take the progression below 1 micron at least.
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I can confirm that 2 micron diamond emulsion paste leaves visible scratch patterns when viewing the edge under a 40x loupe. Looks mirror-like to the naked eye, at least to my eyes.
 
Yes. I agree that every grit will leave scratches that are appropriate to their micron size. That said, the scratches that I'm seeing are obviously larger than that. Sometimes I can even count the number of strokes taken by counting the number of scratches left behind.
 
Might also be issues of how tightly (or not) the grit size is graded in the compound. It might be nominally ~3.5 micron. But there might also be a scattering of both smaller and larger particle sizes in the mix. That's actually pretty common in all but the most tightly-graded (and more expensive) compounds.

Don't know if it's possible, depending on whether or not you have other clean, bare strops in the same leather. It would be easy to rule it out, if you could test the bare leather for scratching, before adding the compound. And if push came to shove, you could also strip them down to bare, clean leather again, by sanding or scraping, and try the scratch test on the leather again. If the strops are contaminated with coarse grit, then resurfacing would be the next logical step anyway, short of just replacing them.

Another option: try the compound applied on a clean sheet of paper (printer/copy paper) and see if the same type of scratches are still showing up. Might even lay the paper over different backing substrates (like leather, then wood, then glass, etc.) and see if there's an influence introduced by the hardness/compressibility of the backing.
 
I've done that a few times with no success. I believe it's not contamination or emulsion/paste issues, because when I apply the same stuff to balsa, I have not problems and see no aberrant scratches.
 
Not sure what's happening, but one possibility is that the balsa isn't hitting the bevel perfectly square, and thus not really polishing. Leather, being more pliable, will make up for very small variations in angle. So you *may* be exposing existing scratches with the leather that aren't being revealed with the balsa. Might be time to sharpie the edge and make sure the balsa is hitting square.
 
3D Anvil said:
Not sure what's happening, but one possibility is that the balsa isn't hitting the bevel perfectly square, and thus not really polishing. Leather, being more pliable, will make up for very small variations in angle. So you *may* be exposing existing scratches with the leather that aren't being revealed with the balsa. Might be time to sharpie the edge and make sure the balsa is hitting square.
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This is why I like hard stropping (wood vs leather, etc.). With a hard/rigid strop you are either flat/square on the bevel, or you are not and you should learn to feel the difference. Easier in my mind to effectively accomplish the goal of NOT taking away from the initial effort put in to creating a crisp apex along entire edge.
 
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