stropping

[Noah Wagener]

What is happening with a strop? That green paste is the same size as a fine synthetic finish stone so why not just use a stone? Doesn't the strop contact the edge itself rather than just one plane or the other that a stone would? Doesn't that round the edge?

And what about unloaded strops? What is being accomplished? Is there anything i can use besides leather to get similar results after an Arkansas stone? Like a really hard stone with little abrasive action?

[David Weaver]

The compound does cut a little less deep on a strop than on a stone, but it also rounds the edge a little. How much of each depends on how much pressure you use and how hard the strop (the strop absolutely has to be clean other than metal swarf and green stuff, though).

You can use biggs or owyhee jasper if you want to use something natural that isn't leather. A bare leather strop with light pressure removes the wire edge. With heavier pressure, it has the ability to burnish a little (but if there are metal particles or grit on the strop, heavy pressure can backfire by nicking up the iron or at least scratching it up).

The finer the edge you bring to a strop, the lighter the pressure. When you're bringing a translucent arkansas edge to a strop, for example, very light pressure will remove the wire edge without bending the edge too much. To see what I mean by bending, finish stropping with light pressure on the bevel side of an iron. See how it shaves hair on the bevel side and the other way around. Then lay the iron flat on a strop and with some pressure pull it across a leather surface. Try it again, and you'll probably find that the side that shaves better switched. That is the reason that stropping a razor requires light pressure - you can move the edge back and forth ever so slightly.

[Ryan Mooney]

That is the reason that stropping a razor requires light pressure - you can move the edge back and forth ever so slightly.

I've also wondered how much (if at all) this causes work hardening of the edge. It naively seems like it would some but am not sure how to quantify it.

[David Weaver]

I'm not sure how much work hardening it creates, but I think whatever amount their might be is quickly blasted off of the edge from wear in planing.

But I really don't know, nor do I know if a considerable amount of work hardening might be done by something like an owyhee jasper slab, which will step up the sharpness level of a carbon steel iron pretty significantly.

[Ryan Mooney]

Makes sense on a plane edge.. It might? matter more on say a razor or a detail carving tool though.

I thought of it mostly because of experience with scythes where you intentionally work harden the edge; but that's a somewhat more aggressive since you actually peen it (and substantially draw it out some).

Back to Noahs original question and your "rounds the edge" comment - that would effectively be akin to a secondary (or tertiary as it may be) bevel to some extent as well I think which changes how the edge survives some (probably for the better in most cases).

[ken hatch]

I've come to the conclusion that a slight "rounding of the edge" is one of the reasons to strop. Yes it will remove the wire edge with minimum breaking of the edge and that is important but the slight rounding retards fracturing of the edge. I've done A&B tests using different ways of sharpening with and with out using a strop. Almost without fail if the finish stone was a polishing stone the first cut would feel and look sharper than the stropped edge finished on the same stone. By the second, third and fourth cuts the stropped edge would cut better and if examined under a 20X lope would show less fracturing than the non-stropped edge. YMMV.

[David Weaver]

Yeah, it's sort of foreign territory. I've read all kinds of things about razors, like heating the edge on a strop, etc, and I don't know what of that is true. I know I won't ever be able to tell because the edge is cool when I touch it. So little happens with a razor once you have it in good condition that it's really hard to make many judgments. Iwasaki credited a barber on two different occasions with using a (non abrasive) linen and a strop to make over a thousand shaves. I'm pretty sure I could easily go a year with a solingen origin razor and the same, so there is so little wear that it's hard to really quantify anything.

Definitely different on a scythe where you're drawing out an edge. I think george may have told us that such a thing was common with bronze tools (drawing an edge out to work harden it for use)? I don't want to throw him under the bus, because if I got that wrong, it'll be because I didn't say what george said.

There is definitely edge rounding on loaded strops, and even on horse butt strip that's glassy and worn in, there must be some. I can literally tell by sight if a freshly honed edge has been stropped on leather, even if the leather is perfectly clean and doesn't change the polish. I'd assume that's rounding the edge the tiniest amount such that an almost microscopic sliver of light glints back. The strange thing is that it's always a sharper edge than the invisible edge straight off of a stone (which must be an edge that is littered with little steel fragments).

[Ryan Mooney]

Almost without fail if the finish stone was a polishing stone the first cut would feel and look sharper than the stropped edge finished on the same stone. By the second, third and fourth cuts the stropped edge would cut better and if examined under a 20X lope would show less fracturing than the non-stropped edge. YMMV.

What types of polishing stone have you compared against?

I'm wondering how much is the rounding vs the quality of the polishing. I suspect that both contribute at least some (a polished edge would have less fracture points) but don't know how much. Obviously the exact difference is mostly irrelevant in practice but its interesting to learn things

[Kees Heiden]

I've come to the conclusion that a slight "rounding of the edge" is one of the reasons to strop. Yes it will remove the wire edge with minimum breaking of the edge and that is important but the slight rounding retards fracturing of the edge. I've done A&B tests using different ways of sharpening with and with out using a strop. Almost without fail if the finish stone was a polishing stone the first cut would feel and look sharper than the stropped edge finished on the same stone. By the second, third and fourth cuts the stropped edge would cut better and if examined under a 20X lope would show less fracturing than the non-stropped edge. YMMV.

I would guess that you had sharpened the edge to too low a sharpening angle for that type of steel. When you round the edge using the strop you are increasing the included angle. if you had used a larger angle on the stones in the first place, I guess you wouln't see this fracturing within a few cuts.

[jamie shard]

I would guess that you had sharpened the edge to too low a sharpening angle for that type of steel. When you round the edge using the strop you are increasing the included angle. if you had used a larger angle on the stones in the first place, I guess you wouln't see this fracturing within a few cuts.

Maybe not. When the steel goes over the hard crystals, it can put localized pressure and tear out carbides or scratch deep grooves. It seems like the slight cushioning of the strop may give it a softer scratch and work to even out the surface, even if the size of the hard crystals are the same for both the stone and the strop.

[Kees Heiden]

But then I would expect the edge to have these nicks in the first place, but Ken writes that the edge was sharp at first, but fractures after a cut or 2 or 3.

Coarse grit is reputed to leave fractures in the edge deeper then the grit scratches. These fractures are not visible at first, but lead to nicking of the blade in use. But fine abrassives (I don't know how fine) don't have this effect. That's probably one reason why we hone the edge on a finer stone, not just on coarse grinding stone.

[jamie shard]

I think there can be stress fractures from the fine stone that aren't obvious which can get revealed with the first few cuts... but I agree it's probably pretty minor in the scheme of things. So I guess it depends on whether Ken is talking about significant fractures or something subtle.

[Warren Mickley]

All of the effects mentioned in this thread come into play. They all have scientific basis and can be demonstrated. However at the level we are interested, what is most important is experience and discernment. You need experience to get consistent results and you need the sensitivity to discern the effectiveness of a technique. As an example, we do not look at a chart and read 22.3 lbs/sq in. for a certain stone and steel etc. and calculate based on our chisel's bevel surface area. Much more effective is to get a feel for the stone and use intuition to determine the pressure. Try more or less pressure and discern the result.

In historical times some workers used powdered abrasives on a strop to make up for the lack of a fine stone. Some used abrasives that quickly break down so that there were finer and finer scratch patterns as they strop. Today these techniques are much less important because we don't have to pay a month's wages to buy fine, consistent stones. A clean dry strop will give the results we are looking for.

[Steve Rozmiarek]

I always thought the strop was the finishing step, just to polish the edge. I've seen my dad use his jeans as a strop for years, the results are hard to argue with. I'm sure it gets rid of the wire edge, but it also brightens the edge, so I suspect its buffing it. He uses oilstones of some variety.

[Noah Wagener]

So stropping (with unloaded strop) for the most part seems to be for the purpose of removing the wire edge? And a piece of Jasper obviously is working in a different fashion than leather as it has no give to it. Is it that it is virtually unabrasive so that it is not adding to the wire edge like a fine stone might and it is just bending it back and forth till it breaks free? I have a Chinese slate hone that is pretty unabrasive. Could i polish it and use it in the same manner as the Jasper? I have seen a blacksmith on Youtube lay newspaper on his stone and strop on that.

I have been pulling blades along my arm just to see if it matters but it has had no effect. I tried the denim as Steve mentioned and it did seem to affect the edge. It also did seem that you could change the effectiveness from bevel to back with just a stroke. Would denim glued to wood make a decent strop? Some razor guy who sells Japanese naturals explicitly said not to use canvas in bold letters. I would think denim and canvas are pretty similar.

I think there can be stress fractures from the fine stone that aren't obvious which can get revealed with the first few cuts... but I agree it's probably pretty minor in the scheme of things. So I guess it depends on whether Ken is talking about significant fractures or something subtle.

Jaime, i have read that most natural stones leave a softer, more rounded u shaped scratch versus a v shaped, deeper scratch of modern synthetic abrasives. Someone even said that because of this rounded abrasive shape, smaller particles will cut faster than larger in Belgian coticules. He compared it to scratching with the back of a spoon or with a knife.

What is work hardening?