Thursday, January 23, 2020

When I'm not working in the shop I sharpen

It is a sickness, even though I'm not a metal worker nor can I stand endless rubbing of the backs of cutters to flatten them, I have a sharpening jones.

Over on SMC there is a thread on Ark stones. I decided to expand it to include JNats. Here is what I published.

While natural stones have been around much longer than synthetic stones they are not as easy to classify and to understand. The other thread on the forum about Ark stones sent me to the shop this afternoon to check a couple of things out. I like natural stones for honing and polishing and will normally use man made stones to grind. For grinding the most important thing is speed with less importance for the scratch pattern as long as it isn't too deep or inconsistent. For honing and polishing speed is pretty far down the list, what is important is the scratch pattern. How deep, how steep, and how random the scratches left by the stone are the three things that determine the quality of the cutting edge.

Synthetic stones are easy, a 5,000 or 10,000 grit stone is, within reason, pretty much like any other stone of the same grit. So the sharpening process is easy to figure out, a 1000 grit to grind, a 5000 grit to hone and a 8000/10000 to polish and it makes little never mind what make of stones you use. Heresy I know, one of the reasons civil wars are so ugly is because they are fought over such small differences.

With natural stones grit has no meaning. Sometimes you will see a grit range assigned to a stone but what that is telling you is the stone may give a finish similar to a synthetic stone of that grit range. The only real test is to take metal to stone and see what it does.

With Ark stones specific gravity can be a good starting point, the higher the specific gravity the finer the stone will usually cut. With JNats hardness can be a clue but so many things can affect the quality of the finish the only way to know if a stone is a soul mate is to use it. The reason for that is in the structure of a JNat. A synthetic stone is made of sized grit particles that break free during the sharpening process and while they will break down some they remain more or less square particles. A JNat cutting particles are flake like and while they do not change much in size in the slurry they do get thinner and because they are flake like the scratch pattern is smoother.

This is just my opinion with nothing to back it up but one of the reasons synthetic stones give such a shinny surface is because of their sharp sided scratches. With JNats some of the most prized stones leave a Kasumi or cloudy surface. In fact my favorite JNat finishing stone isn't very hard but it makes slurry very easily and leaves a beautiful Kasumi finish and edges that last a long time.



  1. Steve D3:28 PM

    I have my original King waterstones and newer Sigma Power ones that are close enough in grit. The experience and feel are very different between the two stones. The Kings aren't very good with highly alloyed steels.

    I do find that relying on coarser stones of whatever type makes the job of 1000+ grit stones easier and less frustrating. I try to do without guides but once a bevel is set with a guide, the rest of the work is just a few strokes away with a microbevel.

    1. Steve,

      As you can guess I'm a sucker for new stones and what have you. In fact I ordered a new Ohira Range Suita today.

      I saw my first King stones in a plastic box a while back. I was surprised they were still around and you are correct they were not very good stones.


  2. Interesting. I long believed that the flatter the shinier (less scratches), but years ago LV introduced a new rotary lapping machine, which they used to flatten the back of their blades. They claimed a significant advance in flatness and their blades came out a mat grey instead of shiny, Huh?? Been wondering ever since why or how but never really came across a better explanation.

    Bob, back home with a peeling nose :-)

    1. Bob,

      Welcome back. It is good to get away from Winter.

      I could be full of it but, I know something flat sided will reflect more light back at you than something rounded. I expect we have been sold a crock as usual with the mirror finish BS. Shapton stones will blind you with their shine after just a couple of passes on the stone. When you look at the surface with just a 10x loupe you can see ordered deep scratches. It is the same with all grits I've used, as you go up in the grits it is the same, just not as deep.

      If you look at a surface finished on a natural stone, there is not as much shine and the scratches are not as ordered nor as deep and sharp sided. BTW, a strop with "green stuff" acts kinda like a Shapton stone. It will make your surface shine by I think changing the scratches left and not necessarily in a good way. Where a strop helps is in getting rid of the burr without ruining the edge and that can be done with a bare/oiled strop and just a few pulls. unlike the 20 or 30 pulls some advocate.

      As always I could be full of it and YMMV,