Stropping, also honing, in general, is the process of stroking the edge of the sharpened knife with trailing motion, for final alignment and fine burr removal. I'm sure everyone has seen a barber honing his razor on the leather belt, at least in the movies. That is stropping, or honing. If you haven't done it already, next time, when you sharpen your knife, do it and you will be surprised with the improvement. There is another important aspect with honing, already mentioned above. Removal of the burr left by the final sharpener. That can be not so simple using other means, especially when you're using very fine abrasives. With coarser sharpeners, you can either see the bur with naked eye, or feel it with your fingertips, or both. As you go lower (in microns), which is the same as going higher on grits, that burr becomes smaller and in the end you won't see or feel it, or it'll be very hard. There's also a wire edge phenomenon, when the burr is perfectly aligned, forming sharp, but very weak edge that will be gone very quickly, once you start cutting, leaving you frustrated. So, to prevent all those things, you need deburring, which is honing/stropping. Another use of leather strops is to load or treat them with very fine abrasives, to get the ultimate sharp edge. However, that is still sharpening, thus, it will still form the burr, thus you cannot skip the stropping on the plain leather, or deburring by some other method ;)
The key point for everything written below: Use Very Little Or No Pressure, as get get more experienced, you can increase pressure as you see fit, but start lightly. If you have done everything right up to this point, then your edge is somewhere around 1µm, may be less than that. Leather pads are softer than any stone, hence the deformation of the pad. Too much pressure and you will roll your almost perfect edge, making it dull, not sharper. In the beginning, some of the people use too little pressure, that is lifting the blade. Then, you don't get much of the effect. Good rule of the thumb would be to use the knife's own weight. Again, even though the process is still sharpening, this isn't the time when you can use pressure. Also, don't try to take a thick, unfinished edge to the loaded leather. It won't work. I mean 0.5µ CrO powder won't have much of the effect on the edge that was incorrectly finished with 1500 or even 3000 grit. It's just too fine and slow for that. However, if your edge was properly sharpened then you'll get very good results in 5 minutes or so.
Use dedicated pads- One more point, which is rather obvious, but let's mention it anyway. You'll have to use separate pads for each abrasive compound. Mixing and washing don't work here. Get a dedicated pad, for each compound, then sharpen and polish away. Here on the following photo you'll see steel base and two magnetic leather pads, the green one is CrO dedicated pad, the brown/whitish is for 0.25 Diamond Crystals. Plus another leather bench for honing.
Maintaining and cleaning leather strops- As with everything else, if you use those leather pads, they will require maintenance. Besides applying and reapplying abrasive mediums be it CrO or Diamond spray, you have to deal with contamination. As you strop, small particles of the metal are removed from the knife blade and deposited on your leather strop. And yes, that happens to the plain leather as well, just to a lesser degree compared to abrasive charged strops. Depending on the leather type contamination levels vary. At any rate, metal particles eventually affect stropping process, producing scratches on highly polished edges, which is obviously undesirable. What's worse, the can actually damage the delicate edge. So, if during stropping you start hearing screeching sounds, cleaning is definitely way overdue. Use any commercial leather cleaner to thoroughly clean the pad, let it dry and reapply abrasives if that was your abrasive dedicated pad. Under no circumstances wash it with hot water and soap, leather will dry, deform and become unusable. As for the particular cleaner type, I personally use Permatex™ Fast Orange hand cleaner. It is not a leather cleaner per se, but does work wanders for leather stropping pads. Besides cleaning them, they work well as sort of moisturizer, and keeping the pads in a good shape. When to clean is up to you and your judgment, like I said, if you hear metal to metal sounds during stropping, then it's long overdue.
0.5µm Chromium Oxide(CrO) Loaded Leather- CrO I've seen in two forms so far. Powder and liquid. Both are available at Dave's place - Japanese Knife Sharpening. You can use one, or another, or better yet, both of them together. Basically you should rub powder or a liquid into the leather, and in case of the liquid, let it dry. As per Dave's hint I mix them. Gives higher concentration of the CrO on the leather, hence better and faster sharpening performance. Mixing is done on the leather pad itself. I've tried both ways, first rubbing in the liquid CrO, then the powder, or put liquid CrO on the pad, then mix the powder in it and be done with it. Can't really tell the difference in the final result. Second is less messy somehow, that is in my experience. I use my fingertips to do all the rubbing and mixing. CrO isn't that difficult to wash off afterwards. The result is extremely sharp edge, with very high polish. We're way beyond hair whittling here.
0.50µm Diamond Crystal Loaded Leather- Pretty much the same as CrO mixture on the leather, however it is far less messy and in my opinion lasts longer than Chromium oxide. As usual, I buy it from Dave, and I have a pretty solid stockpile, that will last for years. Couple bottles or so. Usage is very simple, just spray on the leather pad, wait for it to dry and strop away. As far as the sharpening with 0.50µ goes, I am very positive about it. Works very well either as final stropping compound when I want rougher edges, or as level before using finer abrasives. Lately, I've adopted a bit more time consuming protocol for high level polishes, that is using 0.50µ followed by 0.30µ Aluminum oxide abrasive film and then switching to 0.25µ diamond loaded strop. In my experience that does produce both, better polish and more aggressive edge. Initially that was just an experiment, but the results were really good and I stuck with it. At least when I want the best polish and finest edge on thinnest edges.
0.25µm Diamond Crystal Loaded Leather- Before this one, my finest edge was done using 0.3µm Aluminum Oxide microabrasive film. Then, Dave (yes, that Dave from Japanese Knife Sharpening) offered 0.25µm abrasive. That was something I really had to get. In theory 0.05µm isn't significant difference, but on the other hand, that 0.05µm is more than 20% difference in final edge thickness, and resulting pressure will be proportional to the area. I've been using it for a while now, and I have to say the results are very good. Improvement is noticeable, in both, final polish and sharpness. Also, one more advantage is that compared to CrO powder or liquid, diamond spray is less messy. Just shake the bottle and spray it on the pad. Which is exactly why I got 0.5µm diamond spray as soon as it became available, and to upgrade my experience with 0.5µm abrasives.
Plain Leather- For stropping, I use various leather strops, bench, and handheld strops as well. Depends on the situation. You can see some of it on this picture. Large, bench strop is used mainly for larger blades, especially for the convex edged ones. The other two are for light stropping and smaller knives. Although, lately I tend to use the bench strop for all my sharpening. Another upgrade I have planned, to get a better quality magnetic leather pad from Dave. Leather itself can make a difference, especially with deburring. Plus, I don't have to keep second bench on the table.
Last updated - 02/22/12