# A Basic Pictographic Musing on Suita Natural Stones



## tgfencer (Aug 29, 2018)

Suita are some of my favorite stones and this post involves some not so coherent thoughts of mine on the subject. Much of it is basic, entry-level stuff, but hey, you can just ignore all of it and just look at some pretty pictures. There are many folks on these forums far more experienced and knowledgeable than I am. Japanese natural stone use- just like knife technique, carpentry, or heart-surgery- is a skill, indeed for some a profession, so please take what I say with a grain of salt as I consider myself a novice journeyman in the subject. Chances are somebody out has an opposing and equally, if not even more valid opinion!

I would also just like to note that I've worked on this piecemeal for a while, so if it seems disjointed, that is why.


MY PHILOSOPHY:
Quality suita can be found coming from all walks of life, from nameless mines to nakayama or ohira, from reputable sellers to auction sites, from gorgeous renge-flecked bricks to non-descript rock-shaped objects, super rare to commonly found. None of these things are guarantees of good suita and none of them are more important than how the actual suita performs in use. I have had blindingly good stones I know nothing about that rival good stones I know everything about. Quality is quality regardless of origin, price, or appearance. Sure, its fun to banter about various mines and compare this suita versus that suita. I myself have been known to enjoy debates about the usefulness of hard suita vs soft suita, strata vs strata, or whether renge actually does anything besides look pretty. But, it should never be forgotten in the endless rat race of revolving stones, that the most important things are whether a stone works for you and your needs and whether you are happy with it.

No one needs dozens of expensive suita, or any jnat really. As I've taken to reminding myself when I see pretty, new jnats I desire tantalizing me with their flat surfaces and four intact corners: Money may buy you stones, if stones make you happy, but expensive new stones don't actually make you any more skilled at using them. There is a great deal to be said for the idea that only by mastering the stones you have, can you truly appreciate the differing qualities a new stone may bring to the table.


MUD:
Discussions of mud and slurry almost always come up when talking about natural stones. This is because it is an essential component of jnats and a rationale behind using them. To quote Jon Broida, if I may, "slurry is important for a few reasons... the most important for me are an even, streak free finish through curves and for filling high and low spots (yeah, i cheat like this). However, i also like it for cutting speed...On naturals, its necessary to build up slurry for grit refinement."

Mud increases cutting speed, refines the edge, and determines the finishing polish. And it smells interesting! However, what kind of mud a stone produces will determine its sharpening/polishing characteristics and what you may or not wish to use it for in your sharpening/polishing process. Thick, viscous mud can fill the low spots on a blade making polishing easier and be more forgiving to inexperienced users. Thinner mud may indicate a harder stone and require more careful attention to technique while working to achieve the desired end goal.

Suita stones can run the full range from mud-monsters (Photos 1+2 below) to whispy, thin black slurry (Photo 3 below). I have found that this often corresponds to how hard or soft the stone is, which in turn indicates the amount of material it releases when in use and the speed at which it does so.

Muddy






Not so muddy





Learning the characteristics of a suita, how it performs with a thin slurry vs. working up a thick mud vs. just clear water, is one of the more enjoyable aspects of jnat ownership. Then, you can combine what type of mud you use with differing levels of pressure to achieve different results. A good example of this is Otto's rather timely video: https://www.instagram.com/p/BmB8ZyHHbIS/?taken-by=toishigram . By the by, if you enjoy high quality pictures, videos, and general chat about jnats, then his page is worth a follow.

Below are two comparisons of ohira suita stones with a thin slurry and then again with thicker mud produced by refining the initial slurry.


















On top of that, understanding when and why to pre-slurry with a diamond plate or nagura can be key to many suita, particularly the harder stones, which can be very unforgiving. I most often find myself pre-slurrying hard suita stones with an Atoma 1200 when I am polishing and wish to ensure that my initial strokes do not cause streaks on the blade. Of course, in some cases, very light pressure and a steady hand may serve you just as well.

Please remember, people often conflate hardness with density and both those things with fineness. While there are some correlations, one does not equal the others. Hard stones are often fine, but a soft stone can be finer still. Each and every stone is a combination of all 3 traits and the trick is finding out how to manipulate the stone to utilize its full potential for the task at hand. I encourage people to test out their suita with a variety of mud conditions and pressure in different orders and on different steels. You may be surprised by what you discover. (For an interesting read on layers, hardness, and other info follow this link to Alex Gilmore's musings: http://thejapanblade.com/blog/2013/01/20/a-little-bit-ab-out-color-stones-and-stratas/).

Harder Nakayama suita without pre-slurry





With pre-slurry (sorry for the poor quality photo, the low-res original just couldn't upload to any decent standard. Its an eyesore, but you get the idea.)


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## tgfencer (Aug 29, 2018)

A great deal is often made of mud color. Dark black is generally prized in suita and usually considered indicative of a fast cutting natural stone. Black is sexy and sure makes for some good photographs.

I have no science to support much of what I'm about to say next and I encourage those with differing opinions or experiences to speak out.

In regards to mud color, I have always supposed that a fast initial black slurry is made up mostly of metal particles and a lesser amount of stone material, which would indicate that the stone cuts fast but might not yet have been abraded enough (or be too hard) to start releasing much of its own materials. In my experience, often an initially black slurry will change to a subtly different color over time, usually into a brownish tone. This happens, I assume, because the material makeup of the mud (i.e. the amounts of metal and stone particles) has changed as I've worked and refined it, thus altering the visual composition. Sometimes, however, the black mud will remain black throughout the process.

Some stones produce varying shades of brown, tan, red, or even green. Presumably this is due to the makeup of the stone and the color of the materials it releases and how they mix with the metal swarf from the blade. This, to my mind, should not be mistaken as a lack of quality in comparison to a stone that does generate black mud. For example, such a suita might be softer and release more of their own material quicker, thus keeping the slurry from turning black.. Needless to say I am no expert, but the main point I'm trying to make is that while social media may have a plethora of pretty photos of stones with black mud, there are more important indicators of performance.

While a suita's inherent traits cannot be altered, there are several important factors that are down to the sharpener which can affect mud development, mud color, and perceived 'cutting speed' on suita.

-Firstly, the steel of the knife. More wear resistant and alloyed steels often alter the effects and actions of a stone's mud production, in comparison to a purer carbon, such as white steel. Similarly, soft iron cladding can cause a stone to generate fast black mud whereas a R2, ZPD, or aogomi super may produce only thin swarf on the same stone.

-Secondly, the pressure used to sharpen. A white 2 nakiri I have will produce black mud on practically every medium-hard to hard suita I own with the right amount of pressure, even my nakayamas. However, with lesser amounts of pressure, the same nakiri will produce thin swarf that quickly turns brown.

-Third, and perhaps the most obvious, the amount of steel being put into contact with the stone. Wide bevel polishing will generate more mud faster then simply sharpening the edge, all things being equal.

-Lastly, the state of the stone surface can affect cutting speed and thus speed of mud development. A rougher surface will inherently cut faster than a very smooth surface.

As with everything else regarding suita and jnats in general, discovering these things about a particular stone comes down to testing, testing, and yes, more testing.

Black Mud-
(Fast initial slurry that has begun to thicken as its been worked. It will, on this stone, eventually turn a dark, murky brown if I work it long enough.)





(A hard AO renge suita that never made thick mud, because it doesnt give much up by way of releasing its own material, thus always made dark black swarf.)





Brown Mud-









(A softer stone, this uchimugori releases so much material that it makes copious thick mud within a few strokes as does the hideriyama suita pictured again below it.)


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## tgfencer (Aug 29, 2018)

INCLUSIONS:

Next, we have a few examples of inclusions and su holes. Generally speaking, folks tend to suggest when buying stones that you want to avoid those with inclusions or ugly looking su holes. This is because inclusions can contain grit and particles that are coarser than the material of the stone around them, thus scratching your blade when you sharpen. Su, similarly, are voids that can contain or collect loose grit and particles.

Additionally, sometimes these grits can come loose and move around the stone's surface. When this happens, you will know, as it sounds and feels rather unpleasant. While the stones that command top dollar are generally free of such imperfections, many a good, nay, great stone will contain them and it is a simple case of careful management to ensure they do no harm to your work. I would say, however, that I consider purity and a lack of inclusions much more important for any stone that will be used for final finishing. There's nothing worse than a crunchy particle scratching up all your hard work.


Some people believe that su speed up the sharpening process. Aside from potentially providing a rougher surface, I personally don't put much stock in the idea's merit, as I believe there are so many other traits that impact a stone's performance more meaningfully. How can you truly tell if a stone is faster because of its su or because of its material makeup?

Here you see the profile of an ohira suita. The dark brown portion on the left hand end of the stone is a big inclusion, as are the few other spots that clearly stand out. Whether they are toxic or benevolent- i.e. coarser or finer than the rest of the stone material- and whether they will require removal (by my grandchildren when they wear it down that far) remains to be seen.










The following picture is a good example of what empty su and inclusion-filled su look like on the surface of a stone. In the center foreground of the first photo is a V-shape made by two benevolent lines. On the left of the V are two su that I picked clean of inclusions. On the right of the V, is what appears to be a su with inclusion. As of now, the right su has caused no problems. It may never be a problem, as not all inclusions are harmful, but if it is, I will simply clean it out. The work is really very minimal and considering this suita stone is soft, fast, and a kasumi fiend, it just goes to show that purity and looks aren't everything.


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## tgfencer (Aug 29, 2018)

CURING/LAQUERING/SEALING:

Generally speaking, sealing all natural stones is recommended. Do all of them need it? No. Is there a definitive way to tell if they need to be sealed or not? No, so why not add a layer of protection to your investment. I know one or two folks who have never sealed their stones and have had zero problems and I know folks who have sealed their stones and do have problems. Neither way is any guarantee against breakage, but I tend to err on the side of caution. This goes double for suita in my opinion, which are made of compressed layers of material, often clearly visible. This makes them susceptible to damage in a different sort of way then say, a red aoto which may have a chalkier substrate makeup that lends it to impact damage or flaky pieces coming off of missing corners. Suita are generally pretty hardy stones, but there have been several cases of suita stones shearing apart horizontally along one of these layers. Additionally, su, cracks, and inclusions on the sides and bottom of the stone can allow water into the interior which may eventually cause splitting.

Examples of suita layers-

















(Here you can see a layer in the suita that has some small holes in the side. However, since its lacquered, the water beads on the outside rather than penetrating in.)





The one exception I occasionally make to my hard and fast sealing rule is for harder and/or dense suita. I still tend to seal them at some point, but I don't always feel the drive to do it right away because water has more trouble penetrating into them. If you aren't sure, a very unscientific litmus test I sometimes use is to sprinkle water drops on the surface of the stone and see how fast they are absorbed. Repeat for the sides of the stone. Then go back and with wet fingers wipe a nice layer of water across the surface, just like if you were cleaning it off. In either scenario, if the water absorbs quickly the stone probably ought to be sealed before significant use.

(A dense, somewhat hard nakayama renge suita that I have used for about a year and not yet sealed.)





(The sides of the suita show how tight and densely packed the layers of this nakayama are, compared to some of the larger layers in the ohira suitas in the previous section.)





Cracks are a more worrying prospect. They a danger point for natural stone breakage as they provide water access deep into the stone and are susceptible to blunt force. CA glue is what I use to fill cracks that are not on the surface of the stone. Its cures very fast, it is waterproof, clear, and provides a very strong bond. If you come across it later on as you wear down the stone, a diamond plate will remove it so you can have a clean sharpening surface. A crack on the surface is pretty much impossible to fix. Certainly, I have not discovered or heard of a satisfactory way to deal with them. All that can really be done is cross your fingers and prepare yourself to have a tomonagura baby at some point down the road.

(CA filled crack in the bottom and side of an okudo suita.)





That's it, folks. Love to hear others thoughts on their own stones and/or see some pictures.


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## Migraine (Aug 29, 2018)

I have a question that I've wondered about for a while; this seems as reasonable a thread as any to ask.

When you seal a stone you put a thin layer of something on the sides. So when you then use the stone, with every stroke aren't you essentially rubbing a part of the steel against that substance rather than stone? Is that not a problem in any way? Also don't you end up each time with some of the lacquer breaking down into the slurry?

I understand it's a very tiny section of the blade coming into contact with the lacquer substance each stroke and since people have been doing it since time immemorial it can't cause any horrendous issues, it's just always been something I've thought about since I first came across natural stones/sealing stones.


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## catalystman80 (Aug 29, 2018)

Thanks for putting all this together! great wealth of information and anecdotes.

@Migraine I could be wrong here since I'm a newb, but seems like most sealed JNATs I've seen also has the top edges cornered off (same as synthetic stones where the corner and edges are beveled), thereby lowering the height of the lacquer (or whatever sealant was used). So when polishing/sharpening, the knife doesn't touch any part of the seal.


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## tgfencer (Aug 29, 2018)

Catalyst is right, its not really a problem. After initial lacquering you often get bits of the lacquer dried on the surface, even when taped, especially around the edge so lapping is almost always required. A lot of people, including myself to various degrees, will put chamfered edges on their stones, essentially beveling them over slightly so they are rounded and marginally lower than the rest of the sharpening surface. This negates any chance of catching an edge and causing scratches or, as you said, getting unwanted lacquer in the mix.


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## Migraine (Aug 29, 2018)

We


catalystman80 said:


> Thanks for putting all this together! great wealth of information and anecdotes.
> 
> @Migraine I could be wrong here since I'm a newb, but seems like most sealed JNATs I've seen also has the top edges cornered off (same as synthetic stones where the corner and edges are beveled), thereby lowering the height of the lacquer (or whatever sealant was used). So when polishing/sharpening, the knife doesn't touch any part of the seal.



God damn it's so obvious when you say it. Thanks!


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## valgard (Aug 29, 2018)

Very interesting view into the way you see stones Todd, and lots of pretty pictures of nice cheese xD.


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## brooksie967 (Aug 29, 2018)

Thanks Todd. Very nice write up. I'd like to add that your comments about brown mud didn't mention anything about oxidization as a result of the type of steel or PH of the stone. I believe that this is a huge factor in this. If you make mud on a stone and let it sit exposed to air i think you'll find that the surface of the slurry browns over time. If you were to then drag your finger through that slurry, the mud under the surface will still be mostly black or at least darker which indicates, to me, that this is oxidization. Give'r a try some time!


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## tgfencer (Aug 29, 2018)

Thanks Jeremy, super useful info there, I appreciate the input. I knew someone would have a scientific explanation or two for some of the occurrences where black mud turns brown over time.

You're saying the steel in the swarf/mud oxidizes and turns brown over time, just as the steel of a knife might oxidize or form surface rust?

Don't why that's never occurred to me before, live and learn!


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## Xenif (Aug 29, 2018)

This was a good read, especially to a suita noob like myself. Now I have an urge to get more suitas


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## Badgertooth (Aug 29, 2018)

tgfencer said:


> Thanks Jeremy, super useful info there, I appreciate the input. I knew someone would have a scientific explanation or two for some of the occurrences where black mud turns brown over time.
> 
> You're saying the steel in the swarf/mud oxidizes and turns brown over time, just as the steel of a knife might oxidize or form surface rust?
> 
> Don't why that's never occurred to me before, live and learn!



Amazing piece Todd and thanks for the kind words. To Jeremy’s point there can be a chemical component to the mud colour. But to your point, I do think of mud colour and composition in the same terms as you do. That is to say a composite of cutting speed and friability which determines the ratio of metal particles to stone particles making up the goop. Some impressive chunks of cheese there too!


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## tgfencer (Aug 29, 2018)

Xenif said:


> This was a good read, especially to a suita noob like myself. Now I have an urge to get more suitas



Haha, well, I don't know if that's a good thing or a bad thing but I certainly can sympathize with the impulse!



Badgertooth said:


> Amazing piece Todd and thanks for the kind words. To Jeremy’s point there can be a chemical component to the mud colour. But to your point, I do think of mud colour and composition in the same terms as you do. That is to say a composite of cutting speed and friability which determines the ratio of metal particles to stone particles making up the goop. Some impressive chunks of cheese there too!



I had always assumed there must be some underlying chemical/scientific processes in play, but frankly I am sorely lacking when it comes to such fields of inquiry which leaves only what I can see and feel during use and the deductions this leads to. I think I was drawn to the conclusions that I made because there is a certain kind of easily comprehended and common sense rationale behind the idea that, hey, I'm rubbing stone and metal together so this mud stuff that's produced must be a mixture of stone and metal. Of course, nothing's quite that simple and I'm sure the science happening beneath it all is interesting!


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## mc2442 (Aug 29, 2018)

Thank you for the post! It can be very difficult getting a grasp on things when you try to dip into the naturals world.


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## tgfencer (Aug 29, 2018)

mc2442 said:


> Thank you for the post! It can be very difficult getting a grasp on things when you try to dip into the naturals world.



No problem. I encourage you and any interested in jnats to utilize the search function on KKF or tap into the knowledge of senior members here. There is a lot of good information and quality opinions out there, of which mine is but one and by no means the best. Research and patience can save you money and keep you from potential disappointment down the road.


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## XooMG (Aug 30, 2018)

Nice photos. My luck with suita has made me a bit reluctant to buy any more, but they are indeed nice when they behave. Thanks for sharing.


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## vinster (Aug 30, 2018)

Nice writeup Todd!

To echo what brooksie and badger said -- some stones will respond (or react) to certain steels more than others. You'll notice it when you try different knives on the same stone, or the same stone on different knives. I've had a few stones pass through that had a strong sulfur smell, too (though it seems to have dissipated over time). When I started with jnats, one of my most used test knives was ginsanko, and as a result I don't think I ever saw a brown or green swarf -- just various shades of grey/black. These days I get the whole spectrum of browns and greeens.

I wonder if that has anything to do with what they say about how some stones and knives make better pairings.

My noob moment -- I always thought su were the tiny almost microscopic holes that you can barely see on the surface of a stone. The actual holes that you can see and feel I thought were something else entirely. The little holes can exist on suita as well as other layers.


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## tgfencer (Aug 30, 2018)

vinster said:


> My noob moment -- I always thought su were the tiny almost microscopic holes that you can barely see on the surface of a stone. The actually holes that you can see and feel I thought were something else entirely. The little holes can exist on suita as well as other layers.



It may not be your noob moment at all. In fact it could be mine. 

Su are small holes that were left behind by escaping gases when these stones were being formed in the earth’s crust. They are associated with Suita stones, but they can be found in other layers also. -Keith Johnson, Jnat Glossary

I had read in places and thus always just assumed that these small holes sometimes collected foreign grit over time after their formation. So I tend to call hole-shaped inclusions on the surface of the stone su even if maybe they aren’t technically. I’m not sure of the specifics, honestly. I would be interested to hear a better answer, as I do not wish to mislead people with my terminology if it is incorrect.

For what is worth, I did once have a suita that had su holes of many sizes all over the surface, I mean seriously like a minefield, and they had no inclusions- but many of the larger su looked just like the holes in that ohira suita I have pictured in the write up where I had to pick some inclusions out.


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## zitangy (Aug 30, 2018)

tgfencer said:


> Thanks Jeremy, super useful info there, I appreciate the input. I knew someone would have a scientific explanation or two for some of the occurrences where black mud turns brown over time.
> 
> You're saying the steel in the swarf/mud oxidizes and turns brown over time, just as the steel of a knife might oxidize or form surface rust?
> 
> Don't why that's never occurred to me before, live and learn!


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## zitangy (Sep 1, 2018)

oops my apologies.. user error..

i am more interested in the PH of the stone as i have seen carbon steel turning brown and of special interest... enhancing the kitaeji, suminigashi... I did attempt to emulate by collecting the mud drying it and then adding some diluted vinegar or lemon juice and a dash of soap liquid.

it does seem that those with fossilized microbial life ( colored dots) does have this property... perhaps that could be the reason why an uchigomori with all the tiny2 red dots is the stone for "chasing the inner cloud"..

have fun...Z


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## PalmRoyale (Sep 1, 2018)

This is my Ohira suita that I use for my oire, atsu and usu-nomis. For a quick touch up of the edge I only have to lightly roughen up the surface with my Atoma 400, 3 light passes over the stone with light pressure is enough. When I do this it quickly forms a light mud that's enough to bring back the edge to razor sharpness. For heavier sharpening I use less water and make a thicker, creamy mud and the stone chews through metal. When the mud dries it first turns a light green/brown and when it's fully dried it's the same colour as the stone.


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