Sharpening with leather. Which side for the jewlers rouge?

M

matthew rapaport

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Jun 23, 1999
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I have a few knives (including a new Tim (Taz) johnson a poor picture of which (my fault on the pic)) can be seen <a href="http://www.quine.home.sonic.net/taz.html" target="_blank">here</a>, that have convex edges and I've managed to keep them sharp (more or less) with a piece of leather and some ferros-metal jewler's rouge. I rub some rouge into the leather and then hold it in my hand forming a concave curved surface (like a stationary slack belt), and then work the edge (backwards) with some wrist rotation so that the edge starts out at about 10deg and ends up at about 20 or so. I think some of you have done some sharpening this way, or with a leather strop that is hung on one end like an old razor strop.

But on which side of the leather do you put the jewler's rouge? The smooth outside, or the more textured inside? In my initial experiments I put the rouge on the inside, and brushed it out with a stiff brush when done. I'd been getting decent results, but then someone told me I should be putting the rouge on the smooth side! Which should it be?

I have gotten some results with this technique on convex edges, but not to bring a really beaten edge back to shaving sharp, only to re-finish an already reasonable edge! Anyone have any experience with this?
 
The only knives that I strop are my swivel knives for leather carving. However, you should strop on the smooth side. Also you can not really "sharpen" a knife by stroping. Meaning that you are not removing any metal from the knife. You are only polishing the edge which is already there. It is one of the best ways to get rid of that last little bit of wire edge after sharpening, and it is good to re-align an edge to make it last longer. But if a knife is dull, you can strop till you are blue in the face and it will still be dull.
 
I put the diamond paste in different grains on the smooth side of the leather. The leather must lay flat on a table to grind a really sharp edge. The surface of the leather is soft enough to build a small radius by its own when you strop with a light pressure. With this technique I get a "hair popping" sharpness on the knife.
If the leather hang down with a radius it is very easy but not desired to grind a radius on the edge. This ends in a rounded edge that is not really sharp.
 
Strop on the smooth side and just to give the final luster to an already perfect edge.
This will give our knife a shaving edge, which is not necessarily the best one.
For push cuts it's the best you can get.
If you must slice through fibrous materials leaving the blade unfinished (i.e. with the stone finish) will leave it rougher and able to bite better into the material you have to cut.
The more fibrous the material, the coarser should be the grind.
It's actually, on a microscopic scale, the difference that there is between a flat ground blade and a serrated blade.
 
I have an old barber's strop and it is made with re-enforcing on the back side so the only place that the compound can go is the smooth side of the leather.

Using this as a clue I always glue my leather on a wooden backing rough side down and use the smooth side for all my stropping.. works great for me.

On the buffer I use a cardboard wheel to strop the edge.
 
My grandfather was a barber for 40 years when
i was about 11 he closed his shop and moved his
equipment home. He constantly used a hanging leather
strop. This was years ago and i was not a knife nut
as i am now. I do not know what he put on it but
it was always smooth side. I did see him sharpen
them other ways but only once in a great while.
Hope this helps.
 
R.W.Clark :

Also you can not really "sharpen" a knife by stroping. Meaning that you are not removing any metal from the knife.
Click to expand...

Many buffing compounds are quite aggressive, CrO which is a common high grade buffing compound will quickly remove metal. The extent to which is does was shown clearly by Lee in his book on sharpening where he shows magnified edges before and after buffing. Even plain leather contains abrasives which remove metal, that is in essense what polishing does.

In regards to which side, the more aggressive compounds usually go on the rough side of the leather. These are your SiC grits and are used on worn edges. They are on the rough side because for one it can hold more abrasive, and two and most important it can easily be brushed out and replaced with clean grit. The smooth side should be your finishing abrasive as for the best quality of finish you want a very level sufrace, this is why the best strops are of highly compressed leather.

Alarion, have you looked at the effect of lightly stropping a coarse finished edge? I have found that it can improve slicing performance. You can go to far and gut the slicing ability if you over polish, but just a few passes on the strop can sometimes make a huge gain in aggression. I am not quite sure why this happens. It is not the removal of a "wire edge", I checked this under magnification. I think it might be just the polishing of the sides of the edge and a slight reforming of the teeth without too much change to their structure.

I have also found that too coarse can be a problem as well. While it is true that the more coarse the finish the deeper it will cut on a given length of edge, it also takes more force to rip it through the material. There is a "sweet spot" of sorts where it has enough bite to slice aggressively, but not that deep that it is too difficult to pull through the material. The same criteria are used in the development of the proper tooth for cross cut saws.

-Cliff
 
Mmh, maybe the micro serrations get well sharpened on their "teeth"...
I never tried this, as when I strop knives it to give a perfectly mirror like surface to the edge. I'll try it! :)
 
Wow, thanks everybody... R.W., I was going to say (but Cliff beat me to it) that this is what the rouge is for, to remove metal so that you can really sharpen the blade, though I wouldn't try it to re-grind the edge.

I know you strop a razor to final polish on the smooth side of a strop, but what I was after was how you use leather and rouge to sharpen a relatively dull blade (though not one that needs a regrinding). Cliff came along and said, in effect, "both." Put the agressive rouge (which is what I have) on the inside, and any final polish rouge (if any) on the outside! That's what I wanted to know, but I'll also try mounting the leather on a flat surface instead of holding it loosly and curved and see how that works out with this particular blade.

I'll report more when I find out if anyone is still interested.
 
Smooth side, and if you have any problems getting the polishing compounds to stick, rub some kerosene on the leather followed by the compound.:cool:
 
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