Long in the past, a vendor of sharpening good sent me a tube of dursol. For purposes of this article, you should consider it the same as autosol. Why? Because, for sharpening, it’s the same other than smell. I didn’t have autosol handy at the time that I did this comparison a couple of years ago, and didn’t consider that many would follow with “how does this compare to autosol?”.
That aside, another thing that I think many fail to grasp is when you’re comparing micron sizes, etc, you’re seeing an incomplete picture – the complete picture is the agressiveness of the abrasive and then how aggressive the substrate allows th abrasive to be. Autosol or Dursol will cut as finely as almost anything else when they’re used on wood or MDF. The substrate is soft enough that the particles stick in it and then they rub the steel. Quite effectively. The other nice side benefit is that when they do, if there’s a foreign spec of dust, it also gets pushed into the wood and won’t automatically notch an edge (but sometimes it does).
Autosol and Dursol are, to the best of my knowledge, about 3 microns and made of an alumina type that’s more like flat discs, so they’re not 3 micron round balls. But the alumina is hard and I’m not sure it fits the desire to make it out like it works finely because it breaks down (plenty of abrasives that are described as breaking into little pieces don’t actually do that).
When used on wood, the action of Dursol or Autosol is lovely. When used on cast, it’s aggressive, but only a little faster. What’s the virtue of cast iron? It’s not universally useful for honing with things like alumina. It’s wonderful with very fine diamonds (like 1 micron or finer). But it’s not good for finishing edges unless abrasives are very small and strong cutting at the same time. It’s also very unforgiving with settled dust or particles (you’ll hear the noise as those notch edges and cause you to go back a step in your sharpening routine).
If you have an interest in using cast iron with small diamonds, then you’ll want cast that’s ground finely, and not just a spare plane sole, but that’s a different subject. I’ve tried both, and a self-made plane sole will generally have abraded ridges (that prevent uniform fine edge finish) while a blanchard ground piece of cast will be relatively smooth, and in a hone sized piece, likely much flatter.
Back to the subject of this blog – pictures of edges prepared with Dursol on cast iron first, and then Dursol on pine. White pine is a bit soft, but the pictures look the same with medium hardwood and harder softwoods (like dry yellow pine).
Dursol on Cast Iron
Compare this Picture to the 8,000 Grit Waterstone
Dursol on Pine
Dursol used on Pine: The abrasive is still reasonably fast (and to get a finish this could, should follow something finer than a typical 1000 grit stone – like a washita stone or a 4000 grit or finer waterstone)
There’s one use consideration – once your edges are relatively sharp, they’ll cut wood, so you’re using the iron on wood flat or dragging, but you can see there’s no burr left behind on wood. On cast, you can do whatever you want – the risk is damaging the edge with rough handling, not damaging the cast.
If you’re curious about the level of finish from 1 micron diamonds on cast vs. the dursol on pine, i can’t find a functional difference – unless you’re using steel with a lot of vanadium, and then there’s no reason to use media other than diamonds for any part of the honing process.
I made this post because fine sharpening isn’t expensive, and Autosol and Dursol aren’t the only way to get these results. Buffing bars with a drop of oil for lubricant will do the same thing when you scribble their composition onto wood.
What often comes after I make the recommendation of one of these polishes on soft or medium hardwoods, though, is: “Can I do ___ instead?” (use the polishes on leather, brass, aluminum, cast – whatever it may be). Most of us have offcuts of wood, and if we don’t – that’s a little odd. The desire to take a suggestion and do something different immediately is kind of annoying, though, but it’s the internet.
All that said, seeing the difference in results above isn’t just a comment to avoid cast with alumina. That’s probably not universally true, either – it’s understanding that the substrate makes a difference, just as abrasive type and size makes a difference. If you have something fast (like the gold bar that works well with unicorn), maybe it’s not so great on a hard surface, but would provide a great combination of fast and fine on a scrap of wood (in fact, it does).
Of Making by Hand with Wood and Steel 