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 Joel's Blog at Tools for Working Wood

The Tools of Stropping  

04/09/2013

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.
Tags:Woodworking Tools and Techniques
Comments: 28
04/09/2013Mitch Wilson 
Joel, any reason to strop if one uses a 0.5 micron lapping film as the final step in sharpening? I understand that the leather has some give, but half micron is half micron. I often use a little camellia oil on the film, just for the fun of it. Instant anti-rust protection.
04/09/2013Jeremy 
Thanks for the post I always enjoy your writing style and depth of information. I don't currently strop.
How long (in minutes) are you talking about stropping on say a 1" chisel after I come off say a 2 sided King stone? Just enough to remove the wire edge (which may already be gone) or raising a new edge?
I've often broken the wire edge on my palm. Would adding some GHC to my palm increase the sharpness or is this a bad (and messy) idea?
04/09/2013Bill McCaffrey 
I have tried and all of the techniques above and have found that its best to let the tool pick it's method. Using a softer strop material works well for curved tools and a harder surface works best for tools that you don't want to put a curved face on. For my draw knives, I like diamond compound with mineral oil on a piece of hard maple with a dead flat surface. I have also found that a good oil finished leather works well on my chisels using compound on the rough side and finish with the smooth side untreated. The oil finished leather holds the compound well and provides a bit of lubrication on the smooth side. I have also used the 3M polishing cloths on delicate edges. These cloths come in 1 micron increments. The sub micron (.3 is smallest I have found) 3M films on granite is the best for large plane blades. I discovered all of these materials from making knives and sheaths, so they were always available in my scrap pile. My view is that there is not a one-size-fits-all here and suggest experimenting with different techniques for different edges.
04/09/2013David Bird 
When you say you, "scraped off a few months accumulation of honing compound and black steel residue from my big strop." How did you do that? What tool did you use?
04/09/2013joel http://www.toolsforworkingwood.com
David,
To scrape off my strop I use an old plane blade. A tiny touch of camber on the blade keeps the corners of blade from digging into the leather.

Jeremy,
See the instructions for stropping using a plain strop by following the link I have at the end of the first paragraph of the blog.

Mitch,
a 1/2" lapping film has no give to it. It works as a fine finishing stone. Which is fine. For curved tools a leather strop will work faster. And for straight tools, as it says in the blog a plain leather strop will remove bits of the wire edge that you cannot even feel.

joel
04/09/2013Andrea 
Hi Joel,
0.5 is the size of each abrasive particle or 0.5 is the average size of the particles?
I ask this because I read several skeptical opinions about green compounds and I also have had bad results with the Lee Valley one.
Best regards,
Andrea
04/09/2013joel http://www.toolsforworkingwood.com
Andrea,
Average size. Also remember that the abrasives are fairly soft and do break down to even finer more uniform grits as you use them. Diamond does not, (not really anyway) and diamond paste also have a fairly large variance of grit size.
04/09/2013Andrea 
Thank you very much for your answer, Joel.
Are you able to tell what is the size of the largest abrasive particles contained in the green compound?
Bes regards,
Andrea
04/09/2013Brander Roullett http://badgerwoodworks.com/blog
I have become a regular stropper and it has made a noticeable difference in my tools.

I do things pretty much as you say above, including the green rouge on leather. I've glued mine to a piece of pine for ease, and I've gone a step further that I haven't seen too often.

I rubbed the green rouge onto the leather, and then squirted some baby oil onto the leather. It emulsifies the green stuff, and it doesn't flake off when I strop. It sharpens just as well, but the surface stays more coherent and less messy (which is why I chose oilstones in the first place, to avoid the mess).

I had read about this tip on a forum I found dedicated to razor shaving, they were talking about their strops and how to create one. The mineral oil (I had left over baby oil from the first kid) seems to work great!

Hope that helps.

badger
04/10/2013joel http://www.toolsforworkingwood.com
I have no idea what the largest size of particle is. but since the abrasive is soft I don't know if the large variance will make a difference. In general honing on a good oilstone, followed by a strop on a plain piece of leather will give you the finest edge. But I think I want to do some proper controlled tests to prove or disprove this.
04/10/2013Andrea 
Joel, if Aluminum and Chromium Oxide are soft, they do not cut steel, do you agree?
I know that the abrasive particles breaks with the use and their size decreases, but come on, also the abrasive particles of a P60 grit sandpaper with use brakes down, but we do not call it a honing sandpaper.
In my experience the Lee Valley honing compound leave scratches like thin hair that I'm pretty sure are bigger then 0.5 micron.
This happen because even if the average particle size is 0.5, there are probably some much larger particles.
So I think it is important to know the size of the largest particles, because they are the ones that produce the major scratches and ruin the sharpening.
Best regards,
Andrea
04/10/2013joel http://www.toolsforworkingwood.com
The way Japanese craftsmen flatten a back is take 40 grit silicon carbide powder, and work the blade back and forth. The SC breaks down as it works and in about 15 minutes you have a mirror surface.
Aluminum oxide and Chromium Dioxide are similar but with different breakage parameters.
If you are sharpening a chisel I wouldn't bother with the stropping compound anyway and I would go straight to a plain strop. And in that case you are just removing wire remnants that you cannot even feel - leaving the edge formed by as fine an abrasive stone as you wish.
04/10/2013Andrea 
Yes, Joel, I had read that method on the Odate book, but I hope that you agree with me that we can not call "honing powder" a 40X grit silicon carbide powder.
Best regards,
Andrea
04/10/2013joel http://www.toolsforworkingwood.com
my point is that SC is hard enough to hone steel but also shatters so 40 grit can end up being a polishing/honing compound
04/10/2013Andrea 
Yes Joel, also a concrete block break down with a lot of use an can become a polishing/honing compound.
Best regards,
Andrea
04/11/2013KC 
I have been using a stropping technique I learned from a carving teacher. He cuts circular disc with a center hole out of matboard. The disk layers are glued together using ordinary PVA glue, like Elmers. Put together as many layers as you need to make the width you want. Mount on an arbor. I have mine mounted on an arbor that I chuck into my cordless drill motor. Use a sanding block to even out the surface then apply honing compound.

I have never had an easier time honing carving tool and never been able to get them so sharp either.
You should consider making and selling these paper wheels. At the very least give it a try!
04/12/2013David Weaver 
The green isn't a dye, it's actually the chromium III abrasive. It crosses (or is probably used much more often) as a pigment, so even a little bit of it and a lot of aluminum oxide will make for a very green stick.

For the folks who don't like the hairline scratches, ask yourself this: if the compound was all chromium oxide and a third as fast, would you like it? Probably not. The al-ox particles in the compound may be as large as 6 microns, I believe, but very very few of them are and the bottom line is that even the crayons with aluminum oxide in them will improve the edge off of *any* stone. Ask a shaver, where you can actually feel the difference in sharpness.

Anyone who doesn't like aluminum oxide can just buy graded chromium oxide III powder, but I think they'll find they like the crayon just as much for woodworking.

As far as the hairline scratches left by a few stray particles of al-ox, they won't show up on a work surface and you really can only see them that well because the surface isn't uniform. They don't even threaten the comfort of a straight razor shave.
04/13/2013Jacob http://www.owdman.co.uk
I see stropping as more to do with polishing than sharpening. It reduces friction at the point of tightest contact between the tool and the shaving, chip, and/or workpiece surface. So even polishing the edge of a cap iron improves performance but has nothing to do with sharpening
04/15/2013abraham 
Actually, honing is cutting and polishing. That is what the green compound is supposed to be. Graded carefully to get the benefit of aggressive cutting and burnishing. As far as LEE Valley compound is concerned, there is very little of any .5 micron size particles in it , at all. The amount of aluminum oxide is the majority of chemical analysis of the product. The chromium oxide is much more expensive. So that is why the ratio; is ,what it is. Both minerals have two separate functions and cutting actions. Polishing is part of their functions.
04/15/2013abraham 
As a matter of fact . This green colored compound is thoroughly discussed on line my many I dividuals. This product manufactured by formax, can be seen for its chemical analysis, by viewing its safety data sheet. It not very proprietary.
If some like it, that's wonderful. As far as the rest of you, their are %100 chromium oxide sticks, that are available. They just are a little pricey!
04/16/2013abraham 
BTW. If polish is what you need there are pure white aluminum oxide still is that are quite fine in particular size. Its used for the the Jewelery industry. It polishes and puts out a different t color profile than chromium oxide. Sort of a bluish tint to the sheen.
There are ratings that are put out by the Amaerican society of industrial engineers, ( I believe that's what their referred as), that rate a level of polish on steel. I believe that a #600 is what they call their mirror finish.
04/16/2013abraham 
@andrea.
Chromium oxide is rated at 9 on the mohs hardness scale. Aluminum oxide is rated at about a 8.5 , on the moths scale. They are both hard. Both can cut. Depending on how they are prepared. Calcined aluminum oxide is the softer alox. Where as aluminum oxide that cuts agressively is called ? It is fire hardened to increase its level of cutting ability. Chromium oxide has the ability to cut , depending on its particular size.
Even though they are considered hard. They are both , about 1/5 as hard as SIC.(silicon carbide). Which In turn is about 1/5 as hard as diamond.
04/16/2013abraham 
@andrea.
Chromium oxide is rated at 9 on the mohs hardness scale. Aluminum oxide is rated at about a 8.5 , on the mohs scale. They are both hard. Both can cut. Depending on how they are prepared. Calcined aluminum oxide is the softer alox. Where as aluminum oxide that cuts agressively is called ? It is fire hardened to increase its level of cutting ability. Chromium oxide has the ability to cut , depending on its particular size.
Even though they are considered hard. They are both , about 1/5 as hard as SIC.(silicon carbide). Which In turn is about 1/5 as hard as diamond.
04/16/2013abraham 
@Joel. Chromium oxide Is normally, used as a natural pigment . So the formax product does not contain an added dye. The color green that you see, is the actual chromium oxide.
Black compounds contain Silicon carbide the Red compounds contain Ferric oxide. The white compounds are usually aluminum oxide.
There are no added dyes, to these compounds.
04/17/2013abraham 
@Andrea. If you.check out the formax green compounds on a number of blogs about the materiel safety sheet on it, you will read that some be live that not only is the product a non .5 um particle size, but far from that. If it was to be that small, than that meant that some would be smaller than .5 um, and some larger.
Some have said they believe that some particle size was over 40 micron. Which would tend to support the scratches that are left behind. Scratches in which the , green compound ,no matter how small the micron size, cannot overcome and remove. Repeating , the chromium oxide does not come near , a.5 um size.
04/17/2013abraham 
@Joel.
In regards to diamonds varying in size. Quality diamond paste or just diamond powder should never vary more than .10 um. For example. A diamond powder rated at .50 um, should have no more than a difference of .40um on the lower end, and no more than .60 um on the larger end of the size spectrum. All diamond manufacturers usually will grade their products by this average method.
04/17/2013abraham 
@Joel.
In reference to the" YELLOWSTONE" product. It is a cerium based abrasive. Cerium is one if the softer abrasives that are used to polish glass, primarily because it causes very few scratch patterns because of its relatively soft composition
That's good. Except it doesn't cut very well, at all.
Under a scope, chromium oxide will look more scratchy, but not as much as silicon carbide, boron carbide, CBN, or diamond. All are fast cutters , but have scratch patterns to them.
Soft abrasive, little scratches, non agressive. No sharpness.
Hard abrasives , quick cutting, with scratch patterns.
04/18/2013abraham 
@Joel.
There are actually very fine stick compounds that are probably 3- 4 x finer than the formax compound.
As a matter of fact there is a red , ferrous oxide that is very fine, along with a white stick compound that have sized
abrasives below 1 um.
All of these abrasives work very differently ,and are focused on certain metals. Some are used for coloring purposes as well as cutting for a particular metal that it is best suited for.
Stainless steel, alumninum, non ferrous metals, titanium....etc.
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