|The last time I wrote about stropping I said that the strop functions as an abrasive and because it is soft, not hard and unforgiving like a stone, it makes it easy to ensure that you are actually sharpening at the cutting edge, and in the case of curved edges as when sharpening carving tools, the give on the strop ensures contact along the curved edge. I also had a link to a lesson on the technique of stropping.|
But what of the strop and abrasive itself? There are two very distinct reason to strop. The first is to ensure the removal of the wire edge that you get when you sharpen. The second is to enable fine sharpening at the edge of a curved tool.
In the former case woodworkers routinely strop as a last step after sharpening chisels and plane blades to get rid of the last vestiges of a wire edge. In the latter case, carvers routinely strop while carving to keep an edge at peak sharpness.
The strop material most people use is some form of leather with some amount of give. Lots of people routinely coat a piece of wood or MDF with stropping compound and use that but my thought is that what they are really doing is creating a fine stone, as the subsrate in this case has no give and you lose the advantages of give. We sell horse butt strops, which are very stiff, with little give, and I think they are the perfect strop. Horse butt is also a traditional material for high end strops, we didn't discover their use, we just brought it back to market. Most strops on the market are cowhide, which makes a fine strop, but it's softer and maybe rounds the edges of tools more. But lots of people like them so obviously the difference between types of leather is subtle. Some people mount their leather on wooden boards to make it stiffer and easier to handle. You don't have to do this with horse but you can if you want to. E. J. Tangerman in his classic Whittling and Woodcarving (a book I have owned since I was 10) points out that you can even strop on your hand, which is of course untanned leather.
The strop can be used plain, or untreated, which will refine an already seemingly sharp edge by whisking away the last vestiges of a wire edge that you might not even be able to feel. This is the best way to strop chisels and plane blades that are basically sharp from your finish stone. You will get a sharper and longer lasting edge.
As we have already discussed, a treated strop, or a strop coated with an abrasive compound functions as a soft stone and using it removes metal and can raise a wire edge. This is what you use on curved tools. Most abrasive of stropping compounds are a fine abrasive suspended in a wax stick or cream. The former is easier to handle, you just apply it like a crayon, the latter I have very very little experience with, I used it once and it seemed more trouble than it was worth as it's messier than a crayon. Some people strop using diamond compounds which are always applied as a cream. Some stropping compounds are very dry and powdery and need special handling to get them to stick to the strop.
The most popular abrasive used for stropping is micro fine green honing compound(GHC). Another popular compound is "Yellowstone" which I have never used. I have no idea what the actual abrasive is in Yellowstone, but some people swear by it.
The green color of the GHC is just a dye, and there are several grades of it. All the woodworking vendors sell the same stuff made by Formax in the USA. It's a 6oz. bar of a .5 micron mixture of Aluminum Oxide with some Chromium Dioxide in a wax crayon. Lee Valley sells the same stuff under their own Veritas brand. Many companies also sell red, white, black, & etc. buffing compounds. Those compounds are all coarser than the green stuff. If you purchase the green honing compound from outside the woodworking industry you might get a coarser abrasive (Formax make two versions). Your want the "Micro Fine" version. For hand sharpening the 6oz size will last years and it's under 10 bucks. For power stropping larger bars are available from some vendors.
There are also less commonly available stropping compounds that are at least as fine as the GHC. These compounds might be finer, contain more abrasive, or be imported.
To use GHC just scribble it on the leather strop. Leather has two sides. The smooth side and the rough side. Which side should you use? I use both sides. I like the rough side because it holds stropping compound well, and I use the smooth side as a plain strop for chisels and final strokes with a carving tool. But it probably doesn't matter. When you use the strop you will instantly see a streak of black steel being removed. This is a big contrast with an untreated strop which basically just rubs off the wire edge. I took the photo above when I was comparing different brands of honing compound. Initially the new stuff, on a freshly applied bit of leather cut a lot faster than my old strop. Then I applied my usual GHC to a fresh piece of leather and WOW my old stuff cut pretty good. Then I scraped off a few months accumulation of homing compound and black steel residue from from big strop and WHAT DO YOU KNOW! - my old strop was working as efficiently as any of the new stuff. Moral: DON'T LET GUNK ACCUMULATE ON YOUR STROP.
One more important point to realize is that for regular woodworking tools that you have carefully honed on a 8000 grit or better water stone, or that prized Arkansas stone, until you cannot feel a wire edge, if you strop on a treated strop you can easily create a wire edge, which has to be chased and removed.
Note: The honing bar in the photograph is about 2 ounces and far smaller than the bar we sell. It's a sample size that we used to include in our "Start Carving Now" kits and I'm just using the last few ones we have up.
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