Thread: Matching steel types with natural hones

*Arkansas stones - generally cut steel well up to about 60-62 hardness. When you get to 62, the stone is switching over to burnishing. If you sharpen something like a cheap pocketknife, or even some decent ones, they're softer to avoid chipping, and you'll find that they don't take a great edge off of an arkansas. If you slurry an arkansas, it will cut harder steels, but I'm not sure what's going on. It could just be abrading off the carbides whole by beating up the matrix holding them. Turkish oilstones are sort of this slurried arkansas stone feeling naturally and have a past reputation of being great for honing (I think the word grinding is used in holtzapffel) hard tool steels.

* slates - same as arkansas stones, but usually less aggressive and the quality of the burnishing isn't as good

* Jnats - some aluminum oxide in them (natural). Very dependent on binder, but the good ones will cut stones a couple clicks harder than arkansas stones. When you get into the ultra hard stuff (chisels rc65, etc) they struggle. The higher the hardness, just like arkansas stones, the finer the edge will be until the stone runs out of gas at a certain hardness level

* coticule (not sure, never paid attention. Probably will go a little higher than arks, and I'm sure edge fineness is dependent on the steel hardness). Prefer not to use them except for razors because they're outclassed by other naturals for woodworking and knives.

* Phig - same as the above stones, but seems to be slower earlier. Slurry them and put soft steel to them and you'll find out they're not that fine

* Agates, jaspers, etc. (inculding the non amalgamated chinese jade-ish looking stones) - softer, runs out of steam below the 60 hardness threshhold, but same holds true -the softer the steel, the deeper the grooves. Slurried jasper is really aggressive, slurried chinese agates feels like rolling something around on plastic pellets (and the result isn't very sharp). No great virtue to these stones except as a burnishing plate. Their particles aren't that small if they get loose. Jasper makes a wonderful burnishing plate, but it's much harder to lap than novaculite. Even the most burnished jasper will still blacken quickly with 55 hardness steel, though.

* Synthetics that are not diamond and not silicon carbide - almost exclusively some kind of alumina, and not that different despite all of the market claptrap. They will all cut chromium carbides, and won't cut vanadium carbides (which are only common in huge amounts in turning tools, anyway). They still have varying cut depth depending on hardness of steel (they will cut 56 hardness steel really fast, and 66 hardness steel fairly slowly). Abrasive itself is similar across the board, but binder makes the difference in how a stone feels and how it cuts. Hard stones with a fresh surface cut fast and deep, soft stones (like king) a little more matte, and fast only compared to a loaded stone. Since the particles are smaller in synthetic finishers, and since they cut hardened steel deeply, the variance in edge fineness is a lot smaller with different steel hardnesses.

* silicon carbide (crystolon, carborundum) stones - stronger cutting than "ceramic" and white alumina synthetics, abrasive breaks, stays sharp - makes deep grooves. Can cause a brittle edge on the hardest steels, which is a pain, because some of the hardest steels won't sharpen quickly on anything less.

* Diamonds - cuts anything, any carbide, fast. Still cuts faster to a point if the steel is softer (just digs in deeper). Steels that only burnish on natural stones of any type (HAP 40 / M4) cut on diamonds easily, but they have a horrible tough wire edge. Super hard steels that are not highly alloyed require judicious use of diamonds because the coarse work can leave an edge that is brittle and that will fail during finish work. A pain. Iwasaki's hardest comes to mind (I don't have it) as do the makers of japanese tools who really push their tools way up to high hardness levels (I have those, they're intended for careful experienced use).

No allowance is made for low quality steel or poor heat treating (which leads to poor steel characteristics at proper hardness) in the above - it's not as common as it's made out to be.

From a practical standpoint, it makes more sense to just find a stone that works well with a razor and use the two together than it does to guess at what will work from a spec sheet. Not all sheffield razors are soft and not all tokyo razors are super hard. Plus, you can still burnish the hardest steels with very hard natural stones, so if that's what you're after, you don't have to adhere to the rule of friable stone for hard steels.