how do oil stones work?

[Matthew N. Masail]

I've been wodering... water stones have abrasive with a binder, that makes sense. but oil stones cut... stay flat indefinitly (right?) and still cut (do they have a life span?)... so how? I would think that whatever abrasive partical they have in them would
wear to a point where it's so fine it's pretty much useless for removing metal... what am I missing? are they just THAT hard..?

[ian maybury]

Can't be sure, but I think an oil stone is the equivalent of a grinding wheel with a harder matrix. Which means that fresh grit is not exposed so often, so it doesn't cut as well.

The oil stops metal powder from clogging the stone, and helps move it away. The lubrication effect and/or resulting oil film no doubt reduces friction, but maybe it does other things too?

ian

[Ryan Baker]

Oil stones wear just like water stones -- they just wear much more slowly and take longer to cut. You still have to flatten them. Other than being a different material, they really work the same way as a water stone.

[David Weaver]

They are like any other stone, except the binder is natural. The abrasive is a rounder and softer abrasive. When they are scuffed, they will cut just about anything and fast, but coarse, too. When the abrasive settles in, they cut slower and flat, and the finer stones half cut half burnish.

They are particular about steel, anything tougher than O1 is boogery, and even O1 is not as good as vintage steel.

If you try to do the "remove the scratches with finer scratches" with the oilstones like you can with fast cutting but fine alumina waterstones, they will drive you nuts.

They will go out of flat eventually if you don't use them with some care. With the finer stones, you keep them flat by being mindful of where any gradual high spots might be and you use those spots. A dry lap across a fine stone that is not coated with oil will leave a smudge of metal and it's pretty easy to see.

To me, using a single hard arkansas on a hollow grind with one side scuffed regularly and the other side fine makes a pretty good edge. A well worn in black or translucent stone sharpening by lifting the chisel or plane iron just off the bevel and a few light or moderate strokes and lapping the back will make a great edge, and do little to create a secondary bevel (so the next time you hit a stone, the secondary bevel is so small that you can ignore it and hone with the scuffed hard or soft arkansas just like you would if there was no microbevel at all.

All of that said, a good set of waterstones with some sort of alumina is much more practical for a variety of steels, there is just something a little more interesting about oilstones, maybe because they respond to skill so well, and so poorly to lack of it.

http://www.tzknives.com/razorbevels.html

Take a look at the bevels in this picture. Look at the arkansas stone bevel compared to the shapton 15k. It takes some skill to sharpen an edge like that (my go to bench stone is still a shapton 15k, because you get no wire edge with one and can go directly to it from a medium stone). I have shaved off of a translucent arkansas that i have, and I have to say that the keenness of it with patience to get there is better than any synthetic stone I have, and it doesn't razorburn you. It took me a few tries to get to that, though. Off of the waterstone, the edge is the same every time.

And one last comment, the shape of the abrasive in oilstones makes them much more receptive to stropping. If you're using a waterstone and wondering what the big deal is about stropping, you probably will always wonder that until you hone with an oilstone where the edge seems dull, and a quick bare leather stropping makes the edge sever hairs as well as anything you've seen.

[David Weaver]

The most interesting stones I've seen are the Pike washitas. I have only tried one, but it is bizarrely fine, almost as fine as a finish stone. Esoteric now, but washitas are the stones that took over the UK in the 1800s, and the branded washita stones are much different than a regular hard or soft arkansas. A very nice play stone if you can find one for $35 or so.

One other side note, looking at those pictures. You get an idea which types of stones will hold their grit based on how much finer they are on slurry vs. with no slurry. Slurry means the stone itself is scuffed or a second slurry stone is used to generate some loose abrasive in water. Almost any type of stone, natural or otherwise, will cut fast with slurry. The stones that will refuse to release their grit without being scuffed can always create a very fine edge, too. The sypderco is a good example, it is very aggressive when it's new, but it almost turns into a burnisher, just like oilstones, but even finer. AT the level of fineness in that picture, it would drive a woodworker nuts, though - it would make it feel as though you were never going to get a sharp edge.

The chinese 12k is the same type of stone as woodcraft sells, but they are not 100% consistent, they are also picky about their steel and they cut slowly on water without slurry, and coarse (as you can see) with slurry. They are still interesting, though, and sometimes woodcraft will sell the big one for $20. Gives you the natural stone experience without spending a lot.

[Matthew N. Masail]

wow... thank you for the elaborated explanation! I had assumed that Man Made water stones are much finer than oil stones... I guess I was very wrong. and I wasn't sure about plain strops as you said. I plan on getting water stones; a 1200+6000 sigma power, and maybe the 13000 if I can afford it. Functionality is first thing when the budget is tight. but I wonder, out of curiosity, how these compare
to the super fine natural/oil stones. and how does the 1 micron diamond paste compare.... what micron level are these superfine oil stones leaving of the blade anyway?

[David Weaver]

The particles in all natural stones are definitely larger than they are in the micron and submicron artificial stones. The thing that makes them work the way they do is that they wear and are softer, so they don't cut deep grooves.


I'm not aware of any natural stones that have micron sized or sub-micron particles, they will all cut a bit rough if they have fresh particles on the surface. That includes incredibly expensive japanese waterstones, they also need to be able to hold their grit without shedding it to cut fine, the same way oilstones do, because their particles are probably more on the 3-5 micron size.

Diamond paste will cut anything easily, even carbide tooling. It will never burnish like a dulled abrasive will, it's hard to compare them because the abrasive is smaller but it cuts such a deep groove for its size. The harder the surface the diamond is on, the deeper it will cut.

The sigmapower set would be a good one, and if you want to save money, the green alumina and chromium oxide stick the woodworking retailers sell will put a very fine edge on something, just scribbled onto MDF... for about $7. the edge quality between that and the 13k is about the same.

if money is no object, a good stone is always nicer to use, though.

[Steve Friedman]

The sigmapower set would be a good one, and if you want to save money, the green alumina and chromium oxide stick the woodworking retailers sell will put a very fine edge on something, just scribbled onto MDF... for about $7. the edge quality between that and the 13k is about the same.

if money is no object, a good stone is always nicer to use, though.
My experience pales in comparison to David's, but I will add something about comparing the Sigma 13000 to superfine diamond paste or chromium oxide. I believe I recall reading that the abrasive in the Sigma 13000 is around 0.75 or 0.85 micron. In theory, that would make the abrasive particles larger than in the green sticks. But (for me) it doesn't translate to a sharper edge. It's probably the "give" in the leather, but if I strop a blade on leather charged with the green stuff after honing it on the Sigma 13000, the edge gets duller. Especially at the superfine grits, whether the size of the particle is 1 micron or 0.5 micron is not significant when you are comparing different sharpening media and different substrates that you are using. For example, I have no doubt that 1 micron diamond paste will produce slightly different results depending on whether you are using MDF, steel, and leather as a substrate. All of those are likely to be different from the results you will get with a waterstone that has 1 micron abrasive in it.

The 13000 stone is amazing, but is definitely a luxury and probably an overkill for most purposes. I am sure that the 6000 stone followed by a strop will be fine.

Steve

[Zach Dillinger]

They work very well.

[Matthew N. Masail]

I get it now... I was not taking particle hardness or substrate into account, but it all makes sense - I'm glad I asked!

[David Weaver]

My experience pales in comparison to David's, but I will add something about comparing the Sigma 13000 to superfine diamond paste or chromium oxide. I believe I recall reading that the abrasive in the Sigma 13000 is around 0.75 or 0.85 micron. In theory, that would make the abrasive particles larger than in the green sticks. But (for me) it doesn't translate to a sharper edge. It's probably the "give" in the leather, but if I strop a blade on leather charged with the green stuff after honing it on the Sigma 13000, the edge gets duller. Especially at the superfine grits, whether the size of the particle is 1 micron or 0.5 micron is not significant when you are comparing different sharpening media and different substrates that you are using. For example, I have no doubt that 1 micron diamond paste will produce slightly different results depending on whether you are using MDF, steel, and leather as a substrate. All of those are likely to be different from the results you will get with a waterstone that has 1 micron abrasive in it.

The 13000 stone is amazing, but is definitely a luxury and probably an overkill for most purposes. I am sure that the 6000 stone followed by a strop will be fine.

Steve

You're right, to get chromium oxide to outperform the SP, it needs to be done on MDF or a substrate that allows you to avoid rounding the edge. Chromium oxide on leather rounds an edge, and actually starts the path to dulling if it's used for more than a couple of light strokes. If the leather is hard horse butt and it's clean, that can be mitigated somewhat, but MDF is cheaper, anyway, and you can do the back of the chisel on it, too.

There's quite a bit of stuff bigger than 0.5 microns in the green sticks, it's aluminum oxide. They are about 70% aluminum oxide and 30% chromium oxide last I checked. The resulting edge is still as good, though, as the SP. With plain green powder chromium oxide pigment, the edge is several notches up from the SP, but that level of fineness is only needed for razors, and even there it can be a bit harsh to have an edge that keen.

All that said, the SP 13k is probably the keenest easy to use relatively inexpensive fine stone on the market. Put steel on it, rub it some, sharp edge every time.