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The care and feeding of natural whetstones

post #1 of 14
Thread Starter 

I thought this topic deserved its own thread.


I got a little ahead of myself and bought a natural whetstone.  In retrospect, it probably would have been better for me to work with synthetics and improve my technique before moving into the less predictable naturals.  But well, here it is in my house, and I paid a pretty penny for it, so I thought I'd find out from people who have been using them for a while about how to get as much as I can out of it.


The paper that came in the box with the stone says I should lacquer the sides and the back.  I had a summer job finishing furniture in school so this wouldn't be difficult for me, but I would like to find out why this is necessary at all?  Wouldn't not sealing the stone actually speed up the soaking and drying of the stone?  And would this affect the sharpening in any way later on?


If I do lacquer it, I know that the lacquer you can buy in the US is a different material than the stuff that they use in Asia (if memory serves me right, the stuff in Asia is made from trees and bugs while all the stuff that is made here is synthetic).  Would paint-on lacquer that you can buy here (which is actually made from cotton fiber I think) or even polyurethane (if water-sealing is the goal) work?


The paper also says to keep it out of the sun.  This sounds bizarre to me since, even if sunlight can do anything to a rock, it shouldn't do anything to the rock beyond the very surface where the sunlight actually shines on, right?


Finally, some people say you should dry them thoroughly each time, others keep them in water permanently.  Both seem like a pain in the butt.  Would it harm the stone to just soak and use, then allow to sit around like what I do with my synthetics?


Finally, about the nagura stones -- why are these necessary, since the naturals are supposed to raise their own mud as you use them?  And at what grit do you start using them?  Some websites say that nagura stones should be used with polishing stones i.e. 6000 and up, but others recommend them for naturals starting with the Aotos which are only 2000+.  Ultimately the question is what do they really do?

post #2 of 14

I think we're mixing some different bits of information here. I am NOT an expert on natural stones, but I know a certain amount about them.


Soaking: As a rule, you don't soak naturals. You sort of flick water on them and that's it. Some people use more, some less, but it's not soaking. Some stones like a little more than others, but you don't usually sharpen in a puddle.


Nagura: The nagura basically provides a little abrasive mud of its own; as you grind in that mud on the stone, this mud acts to encourage the stone to raise mud. The point being, this is a rock you've got, not a baked brick, and it doesn't want to break down into mud The nagura gets the process going, and once you've got a little stone mud going, the nagura stuff is basically irrelevant.


Which nagura with which stone? That's an awfully good question. But you've got to ask a stone expert: this is a complex issue. As far as I understand the theory of it, you want a nagura that is at roughly the same grit as the stone, preferably a little bit finer. But there are all kinds of variables, and then most things people use as naguras aren't -- they're "koppa," broken pieces from when somebody was making a stone, with sides cut smooth. Proper naguras as such have to have this special stamp thing, and I gather they cost quite a bit too, but I have never actually used one and have no idea whether this is just the usual Japanese thing of getting all-fire worked up about some piece of old-fashioned technical information about which nobody cares any more, so let's claim it's an art form. That's big in Japan, and bigger in Kyoto, around which are found most of the major whetstone mines.


Lacquer: I've seen this, but I don't know whether it's a good idea. If you do it, I doubt that it matters very much what sort you use, as the point is basically to prevent water from getting in the sides, even through just moist air. The thing is, stones have layers, and there is always a chance that you may have a weak layer running through your stone, visible or otherwise. If that layer absorbs water, it could break into mud and split the stone.


Sunlight: the theory is that you don't want to expose your stone to rapid drying of any kind, nor to significant heat. Again, what you're trying to avoid here is cracking and splitting. I don't know whether this one is true, but I for one would not take a chance on it.

post #3 of 14
Thread Starter 

I'm sorry -- I think I didn't state my question clearly enough.  What I meant to ask was not which nagura stonre to use with which sharpening stone -- that would introduce an endless number of combinations, and is pretty pointless since I can really only buy a couple of different types of nagura here anyway.


What I meant to ask was, at what level does the nagura begin to become important?  I seem to only see nagura stones packaged with 6000+ grit stones, but some websites say that you should use them with 2000+ grit Aotos too.  I currently don't even own any nagura stones because I am not entirely certain that I want to go further than the 2000+ that my Aoto will give me, but if it will benefit me even at this stage I'll buy one.

post #4 of 14

Do 15-20 strokes, on one side, in one direction, with your knife. Do you see any mud at all? If not, use a nagura to get the process started.


How high-grit, roughly, is your stone again? Do you know what it's called, what mine it's from, and stuff like that? Just in case someone around here knows more details.

post #5 of 14
Thread Starter 

RIght now I just have an Aoto.  There was a sheet of paper glued to one end of it that says "Kyoto special select" or something like that (don't remember because it's thin paper and went bye-bye the first time I used it with water).  The paper that the company that sold it to me included with it said all Aoto are mined from one particular mountain only.


It's rough on three sides and has a little bit of a crack on one end, so I only use about three quarters of it for the blad, and try to work on the knife tip on that last quarter.  The website said it is 2000-6000 and puts a pretty shiny finish on my edges, so I somewhat suspect it might be in the middle to higher end of the range.


One odd thing about this stone -- it smells like a cut-up raw potato when I use it!  I've taken to calling it the "potato stone." :D

post #6 of 14

Have you actually got a nagura to use? Aoto's are pretty soft, and you shouldn't have much trouble raising mud from one.


As to the grit and shininess, that's misleading. Naturals don't sharpen and polish the same way as synthetics. The only way to make a serious estimate at the grit, other than to say 2k-6k (the rough range on aoto's), would be to compare scratch marks against high-quality synthetics, under a lens. I wouldn't bother, myself.


I'm not entirely sure, but I believe aoto's are used damp. Basically you pour some water on the surface so it stands like a puddle, then wait a minute or so for most of that water to be absorbed. Then you sharpen and the surface raises mud. I think that's right -- anyone here expert with these things?

post #7 of 14
Thread Starter 

I just bought a Takenoko and it came with a synthetic Nagura.  From what I understand it is rates at 6000-8000 (there were no grit markings on the stone or packaging) and should make a good next step up from the Aoto.


I also got a second Aoto to try the "self flattening" thing I thought of, and now I am quite convinced that the first one I got is way higher than 2000.  The two stones feel completely different, and the second one is far rougher.


I also got a table microscope that connects to my PC through a USB port, allowing me to take photos.  I will have this sharpening thing figured out yet.

post #8 of 14

You might be able to make "self-flattening" work for you, but I wouldn't let the stones dish very far.  A 2000# stone is going to be slow as hell.


Further, I wouldn't put too much faith in how smooth the surface of your natural aoto feels as the gauge of its grit level.  Unless the stone is well and truly broken in and/or has had the surface roughed up, you're feeling the lap left by the quarry.  It takes a while to wear off.


I suggest using a coarse flattening plate of some sort to do your flattening.  I usually suggest dry wall screen, but I don't know if it will work on the natural stone.  Since it's only $15 or so for a life time supply, you might want to give it a try as opposed to running out and buying a DMT XXC. 


Getting back to flattening one aoto with another, it's very common to use a coarse stone to lap a medium or a medium to lap a fine, but flattening one stone with another -- unless they're very, very soft -- is not the best plan.  Lapping with a stone one "step" coarser allows you to get a surface which will produce mud quickly but isn't too roughed up.  Your natural likely isn't roughed up enough yet.  Try flattening with an appropriate flattening tool, then lapping with your 1K. If you aren't set up to flatten yet, and both stones are reasonably flat, try roughing up the aoto with the 1K and see if it doesn't produce more mud and become significantly faster as well.


Always make sure your stones are well soaked before flattening or lapping, or they're crack and crumble like dry clay.  


Nobody ever gets to the bottom of sharpening.  It's one of those things where greater knowledge not only breeds greater competence but greater appreciation of the abysm of your own ignorance as well.



post #9 of 14
Thread Starter 

Well, it was a thought...  Like you guessed, the "self-lapping" takes ^$&% forever.  It does seem to work, but I spent so much time grinding the two stones against each other, it was way longer than the time it took to actually try a knife out on it.


The only advantage is that it generates mud automatically, and because of this I can see where they are dished immediately.  It's slight, but already there.


The thing is, this second Aoto is much rougher, so if nothing else I did not really duplicate the first stone, but instead got another grit.  My guess is that the first one I got was 3-4000 and this one is ~2000, maybe even a little lower.  It cuts faster and releases more slurry (I tried both without the nagura first to get a feel for the stones themselves), but is neither as fine nor as dense as the first one -- the weight feels different despite very similar size.


I can see how acquiring natural stones can become very addictive in and of itself though...  Each one is so different from all others, even if they are ostensibly the same type of stone.  Put them together with steel and it's a whole other story.


Off to shop for a can of lacquer and some drywall screen tomorrow.  Thinking about it some more and aynthesizing the information I learned here, I've come to the conclusion that the lacquer really mostly just reduces the available surface area on the stones to slow down both wetting and drying -- by reducing the available surface area for moisture to travel in and out of the stone to one side out of six, the rate of water absorption and evaporation would be greatly reduced, and the likelihood of cracking with each wetting and use should also be reduced geatly.

post #10 of 14
Thread Starter 

Yesterday I got my new stones in.  I hadn't used the Takenoko yet but have already tried the new Aoto which is rougher than the old Aoto.  Today the USB microscope I ordered from Amazon got here.


Here are two photos.  The first one is the Tojiro petty, factory edge:




...and here is my Global after going through the King 1000 and both Aotos:




I am telling you there is no way that first one is anywhere near 2000.  It might be 6000 or higher.

post #11 of 14
Thread Starter 

For comparison, here is the Wusthoff after both Aotos.  Only the most minute scratches are visible, and the finish is kind of...  Cloudy in appearance:




...and here is a different Global (long story...) after only going through the 1000.  You can see a lot of scratches (I thought 200x would be plenty for blades...  Maybe not...):



post #12 of 14
Thread Starter 

Okay I tried out the Takenoko, first without using the Nagura (just wanted to know), and then with.


First impressions: pretty hard stone, doesn't wear as fast as the King, doesn't take much water.  A splash at the beginning gets things going.


For my own edification, I tried one side of a knife on one half of the stone first without the nagura, then rotated the stone 180* and worked the other side of the knife on the other end of the stone with the Nagura (small synthetic block; came with the stone).


Without the Nagura, the stone itself raised very little mud, raised it very slowly, and also cut very slowly.


With the Nagura, there was mud all over the thing right away, and cutting was much faster.  The weird thing is, it also wore faster (the printed logos on one end on which I used the Nagura wore down, but the other did not at all).  And the white Nagura raised grey mud which turned black as soon as I started sharpening.


Which confirms Chris Leherer's information that the Nagura is packed with abrasive particles that wears the stone to encourage the stone to release more of its own abrasive particles.


Anyway the reason why I am putting this post in this thread is to say, after trying out some of this stuff, I totally agree with your posts.  I just had to do it once myself and see first.


Tomorrow I try the Nagura with the finer grit Aoto.  The way that it worked -- tiny bit of mud, very slow cutting -- felt exactly like the Takenoko sans Nagura, so I suspect it will also benefit from its use.  But the second Aoto acts very differently and does not need it.


Fun with rocks and steel! :D

post #13 of 14

Naguras themselves are not packed with abrasive materials -- or at least nothing hard enough to be very abrasive.  The stones are pretty much like chalk.  A nagura itself isn't going to do much sharpening.  What is going to do is break up on the surface of the stone and leave a lot of small particles.  When you rub the knife into them, they rub against the stone and help break up the binder, which in turn helps the stone to make mud.  In other words, the nagura works on the sharpening stone and not the knife.  So be aware that you only want to make enough mud with the nagura to get the process started on the stone.  Also, remember you want the stone the sharpening stone wet -- pre-wetting the nagura isn't a big deal.



post #14 of 14
Thread Starter 

Thank you BDL.  Your input is always appreciated.  I guess the Nagura breaking up the binder is why it also wore the stone faster where it was used.


The finish after the Takenoko is oily slick to the touch.  I can see how this might allow the knife to slip through food the way a rougher surface would create drag, with more delicate foods like fish.


I have three technique questions and one general question:


First, I am still not nearly as consistent as I would like to be with the sharpening angle.  This is actually proving to be a bigger problem as I started to work on thinner knives with more acute edges, because working with a thinner edge, every mistake costs me more than it ever used to.  This is especially hard when it comes to the curved portions.  Is there anything I can do to become more consistent more quickly?  I thought about using a jig for a while until I get more used to the angle, but the size of the petty pretty much makes that out of the question.  I am also building a sharpening box to tilt and elevate the stone so I can see the space between the knife spine and the stone at all times.  What else should I be paying attention to, to get a more consistent angle?


Second, as the knife thins towards the point, I find myself having even more trouble at maintaining the same angle, because the same visual cue -- the width of the space between knife spine and the stone surface -- doesn't work.  Do you have any advice about this?


Third -- gouging -- I put a couple of streaks into some of my stones with the tip.  This never used to happen to me when I was using the one stroke method, but as I work the tip with the standard Japanese back and forth technique, I find that I am sometimes gouging the stone like a n00b.  As horribly embarrassing as it is to admit this after many years of sharpening, I wanted to ask your advice (and the advice from anyone else) about it because I figure it's better to suffer some embarrassment now than to screw up all my stones for years before I learned by trial and error.


Finally, my "curriculum": I've been working on the Tojiro DP petty for a week or so now.  I got it partially as a practice knife -- the plan is that, when I can duplicate or surpass the factory edge on the Tojiro petty, I will move to a bigger knife, probably a bigger Tojiro, and when I can surpass the Tojiro factory edge on THAT, I will get a mid-range knife, and work my way up to a true laser that way (so I don't destroy one of the laser candidates with bad technique trying to learn how to sharpen).


Right now the regime is King 1000 -> ~2000 Aoto -> ~4000 Aoto with synthetic Nagura -> 6000/8000 Takenoko with synthetic Nagura.


Does that sound like a good stone progression and plan?  Is there anything else I can be doing to up my game faster?


Thanks again.

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