Uchiko considered harmful

Uchiko is an abrasive compound that comes with a lot of sword care kits. This compound is needlessly, carelessly and incorrectly applied most times and causes damage to the polish, even when correctly applied. 

It’s an abrasive, there is no getting around this fact and I won’t use it, and encourage other people to not use it.

This little guy here is your enemy:

If you use this tool as part of normal maintenance, over time, the blade image on the left, will end up looking like the blade image on the right.

This is actually a before and after shot of repairing uchiko damage from correctly applied uchiko. Over time the uchiko has caused heavy streaking in the hadori and glazed it over, making it harder to see the activity.

This is just uchiko doing what it does. It’s an abrasive. It’s like pouring fine sand over your sword and rubbing it. It makes no sense to do this to a sword that you just paid a specialist to fix up as nicely as he can, with all his special tools and training and insight.

What follows below is one of my old rants on uchiko, it handles the details well and better to reuse it than write it all over again.

Uchiko Considered Harmful

I have ranted often about uchiko. I am dealing with this again as I am processing some old high quality swords, and uchiko has negatively affected their appearance. I just quickly went through my photo archive and pulled some images to demonstrate why you don’t want to use uchiko and why you should share this knowledge with others, especially beginners who are virtually guaranteed to apply it incorrectly. 

I’ve written this to document in one place my various rants against uchiko and hope this will be google bait, and as such will improve the state of preservation of swords going forward. I think most members here are already of the mindset that a microfiber cloth is a better alternative to uchiko, so this is more written to present to the beginner who may be distracted by old advice that uchiko application will improve their sword. So this is my counter-argument to that advise for posterity and to try to do a bit to stop the insanity that I regularly see when swords pass through my hands. 

The Bad Old Theory Is Without Fundamental Merit

Some old postings on the internet by guys who meant well but were a bit misguided implied that you can improve a polish through the use of uchiko, and that constant uchiko use over the life of a sword would cause its look to settle down and be something that could be more appreciated. 

This is false.

There is a degree of subjectivity to this: some people like things done in a certain way. For instance, you may want to pour a bottle of ketchup over your $100 steak at a high end steakhouse in New York (2017 note, I wrote this originally in 2015 before it was known that a certain famous leader liked his steak like this).

You may think stripper shoes are appropriate evening wear to a black tie event. You may think sandals and white athletic socks is a rocking look (it is comfortable though). These are subjective opinions so are in some sense completely acceptable, but they are prone to mockery because they illustrate fundamental misunderstandings. 

Some of these misunderstandings can be perpetuated by things like old advice postings saying “this is the way to do it” or the momentum of “this is how we have always done it” when there are in fact advancements and enhancements that come along and should be adopted. 

What Polishing Is

Polishing or finishing – whether that be a sword, or a diamond, or furniture – shares some fundamental principles over all these domains.

It is a process of leveling a surface.

This process begins by using a coarse abrasive substance to grind a surface to a uniform state of scratches. It then iterates by increasing the levels of fineness in the abrasive, and thereby creates finer scratches and a more uniformly leveled surface.

At each iteration of this process, it will knock off the high points, and create gouges in their place, while leaving gouges already present in the surface untouched.

By creating ever finer gouges, the highest points eventually become approximately equal to the lowest points. This process can proceed until the gouges are so small they cannot be picked up with 10x magnification and the surface to us would appear to be perfectly uniform (as in the case of polishing a diamond).

With metals like gold or steel, burnishing can be a final step, in which case a hard material with a smooth surface is rubbed over the target surface. This creates some melting in the surface of metal due to friction, which will make the very finest scratches flow together into a perfectly even surface.

In the case of furniture, wood is polished down in the same way through iterations of ever finer abrasive until it appears to be smooth (in which case the texture of the wood fibers is much greater than the scratches being placed into it by the abrasive). 

The final stage of wood polishing and sword polishing involves some additional dress of the surface. In swords nugui and hadori processes are applied to dress it up. In furniture, a finish (shellac, or polyurethane, or varnish, or lacquer, or oil) is applied which will solidify and can then be polished. Since a finish can fill gaps in wood grain, it can further level and be completed into a high gloss finish. High gloss is achieved again by creating ever finer and finer scratches. As well a matte surface or a semi-gloss surface can be achieved by rubbing the finish with a slightly coarse abrasive.

What all of these things do is to alter the way light reflects from a surface.

Gloss and Frequency

A high gloss surface has extremely fine scratches in it. The finer the scratches, the more even the surface… it begins to approximate being perfectly flat. This makes photons hitting the surface reflect in a predictable manner.

That is, angle of incidence and angle of reflection are approximately the same for a high gloss surface as they would be for a theoretically perfectly flat reflector (a perfect mirror). Gloss is something that appears in the micro-texture of the surface. A spoon is not flat on the macro texture: it is curved. But the micro-texture of a steel spoon is generally glossy (until it is used a lot), so we see clear reflections in it. The only distortions are made by the macro-texture (or the shape) of the steel.

A sword, when being polished, has the polisher adjusting the macro texture first. These macro and micro textures are basically frequencies of distortion in the surface and they are layered on top of each other. 

A sword may be bent for instance, which represents a very low frequency roughening of the surface. The defect in the surface is much larger than the surface itself. It may in fact have one peak, just a simple bend. The wavelength of this frequency would be twice the length of the sword, so in the case of a 70 cm sword the wavelength would be 140 cm for a simple bend in the middle. The wave is adjusted by reversing the bend until the sword is straight. Thus the lowest frequency defects are addressed. 

General shaping of the surface now takes place. There was an example recently of an Akihiro that was poorly polished and the coarse stones used dug deep into the unhardened areas of the ji in its hitatsura, and tended to glide over the harder areas. This creates a middle frequency defect in the surface, where if you counted the peaks and valleys in the surface, maybe there would be one peak every 2 cm as you hit tobiyaki.

Between the tobiyaki where the stones dug in you get a valley. So one peak and one valley is one wave, the wavelength of this defect would then be about 4cm. Both this and the bend are macro-textures. They do not affect the scattering of light but they affect the geometry of an image being reflected out of them. You can consider a mirror with waves in it will clearly reflect your face but the geometry of your face will be distorted (the spoon again, or ripples from a rock cast in a pool). 

The polisher’s goal is to continue to tackle these defects into ever finer stages until they are very small, and very uniform. At this point the application of burnishing and hadori makes for a mirror surface where the polisher wants it, and a fine textured but evenly roughened surface in other areas intended by the polisher. In polishing anything the aim is to make successive iterations of:

  • controlled uniform size scratches
  • scratches that follow the same general direction (though this is not absolutely necessary if the scratches are fine enough… for instance a random orbital sander on wood, provided the scratches are uniform in size)

This gets us back to gloss. The higher the gloss (i.e. the flatness of the micro-texture) the more predictably uniform the reflection of light. The rougher the micro-texture the less predictably light will reflect from it: basically, the light will scatter. 

The more light scatters, the clarity of a reflected image will be affected, the color will desaturate and white out. To think of a metaphor here, look out your window on a sunny day at noon and you will see a clear image with highly saturated colors. Now, start some snow falling. The snow captures sunlight and reflects it at random angles, scattering it. The more snow in the air, the scene starts to white out. Similar effects can be had with smoke or clouds or fog. If the random reflection of light overtakes the predictable reflection of light by a large margin (i.e. a blizzard) you will lose the image entirely. It’s a white out. 


Hadori reflects light randomly because of its scratch pattern being more coarse than that in the ji and having no specific orientation. The orientation of scratches may allow a surface to appear to be smooth under some lighting conditions, but may be revealed at other angles when light catches those scratches. Often times poor polishing skill in the boshi of a sword is revealed in this way, because fine scratches will appear at a certain angle of the light and this is a very difficult surface for a polisher to adjust. This is not ideal for something like hadori because hadori should be visible at all orientations of the light, hence the scratch pattern having no orientation of its own. 

If hadori is “too thick” people complain about not being able to “see through it”. Uchiko can reduce the hadori because uchiko is an abrasive, and successive applications of uchiko will take the random scratch pattern in the hadori that reflects light in all directions and will eventually smooth it out by continually abrading it. If the uchiko is very fine and high quality this will make the applier feel that they are “improving” the polish. 

In fact they may be improving the polish, but only if the polish was a bad polish to begin with.

Or if there is no polish at all. 

The real solution though for a bad polishing job is not to use uchiko but to get a good polish in the first place.

An Imprecise and Unpredictable Tool

A sword polisher is buying stones that have a high degree of uniformity to their textures. This will create a uniform scratch pattern and improve the quality of his polishing. One may consider that the most high level polishers will also be attempting to use the best quality tools – it is essential because their skill may be so high that it exceeds what their tools are capable of.

For instance, if I am to polish a sword, it would not matter if you gave me the worst stones or the best stones: the result would be a disaster of epic proportions either way. If I were to train for long enough, my skill would begin to approach the quality of my tools and the disaster would lessen until it was passable. If I trained long enough and had enough talent, I would exceed the capabilities of the poor quality tools and would require higher quality tools in order to express all of my abilities. 

Uchiko is not a tool with a high degree of control.

Through its application it is concentrated in certain areas of the sword by the application process (tapping an uchiko ball against the sword). It is not perfectly randomly distributed over the surface to begin with. It is then wiped linearly over the sword with a cloth. This cloth collects the uchiko: at the very beginning the cloth has no uchiko on it, and by the end of the stroke the cloth is fully loaded with uchiko. This means that no surface of the sword is being addressed by the same amount of uchiko as the cloth is constantly loading as it goes.

Depending on the grip, and the fact that fingers are not uniform surfaces, this uchiko is pressed against the surface of the sword with different pressure at each contact point, meaning some areas will gouge deeper than others. Finally as the cloth passes over intentional defects in the surface (like horimono) and unintentional ones (like ware), the uchiko will be pulled off of the cloth, creating voids in the abrasive being dragged over the surface of the sword. Imagine a snowplow pushing snow, now imagine that you remove the center section of the snow in the plow and create a void. As the plow continues to push, snow from the sides of the plow will pile back into the void and fill it up again. 

So what happens as uchiko passes over a defect in the surface is that this void in the abrasive will create a clear drag zone after the defect.

Wherever there is abrasive in the cloth, the surface will continually haze over with each successive application of uchiko. This will make the steel more gray, more light, and show less contrast. Where the drag zone is, the original polish will still show through for some distance past the defect. 

The result is now a non-uniform surface where some areas have been hazed (brought to a lower gloss) by the uchiko and in the drag zones the original gloss level shows through. 

Oil and Uchiko = Problems

Swords are generally oiled. Application of uchiko onto an oiled sword does two things:

  1. it gets oil on the applicator
  2. it mixes uchiko with oil on the surface of the sword

Whenever uchiko mixes with oil you get a slurry. This is a thick, viscous, evil, abrasive compound. Since you are wiping it over a surface that has texture in it (swords have fine texture and are not perfectly smooth as previously mentioned: horimono, defects, and also just grain pattern), the low points of the texture will capture the slurry and the pressure from your wiping will force the slurry into these defects. Once in the defect, it will stay. It will also attract ever more since oil is sticky.

Once those defects trap enough uchiko slurry, when you push a sword into a shirasaya, the greater and more even pressure of the shirasaya against the sword, and the fact that the inside of the shirasaya also has texture with fibers that are elastic, the wood surface can penetrate into the defects and scoop out uchiko slurry.

Now you have a high pressure surface (shirasaya) pushing abrasive uchiko slurry that has concentrated in a repeated fashion in the same places in the sword, over the surface of the sword after scooping it out to some level. 

That will scratch the surface of the sword in regular places. If it is a thick chunk of slurry that becomes trapped into a defect on the inside of the shirasaya, you effectively get a polishing stone stuck in the shirasaya and this will rub the high points on the sword leaving long, thick scrubbing marks. 

If it is distributed over the entire inside surface of the shirasaya, then it will just scratch the sword like you are rubbing sandpaper over it.

Furniture polishing has the same type of problem, when sandpaper collects wood dust and the dust sticks to the paper, it forms a slurry of dust and abrasive which gets knocked off the paper. These form concentrated nuggets under the paper that are called corns. The corns in turn  create linear scratches in the wood or the finish. If you have an orbital sander, then corns form squirrely circular orbit marks and completely destroy the finish.

It’s why you have to be careful when using sandpaper and discard it once these corns start to form or else you’re just working against yourself.

The last note here is even if the uchiko slurry embeds in the texture of the sword without being displaced and causing scratches, it will ruin the appearance of the sword because you start looking at uchiko. This can form white spots and lines and rings in the surface of the sword. It makes the sword look tired when it may not be tired at all.

If the surface of the sword is extremely fine grained and even like Awataguchi or Hizen, if you do not remove absolutely every last tiny particle of uchiko before the sword goes back into the shirasaya, that uchiko will end up in the shirasaya and easily cause visible scratches in the sword. I do not know very many men at middle age with eyes having lost their youth who can be confident of removing every grain of uchiko dust out of the million or so that may be sprinkled over the sword when the uchiko is applied.

And that perfect action has to be performed every single time or else you have a guarantee that uchiko goes into the shirasaya and becomes sandpaper on the finish of your sword. 

Even if the application of uchiko is done correctly, it is still a linear abrasion of the surface. This will cover the surface with fine linear scratches. Before this abusive treatment the ji would have appeared clear of scratches if the polish is good.

Fixing What Ain’t Broke

If I took my car into a body shop and asked for the most talented painter in the shop to repaint my car with a high quality custom paint job, then I took the car home and rubbed it with sandpaper to “improve” the paint job, I would be considered somewhere between crazy and stupid.

Or at least misguided. 

If I brought an antique piano into a restoration shop and had a man with 30 years of experience perform a painstaking french polish in shellac on it, then after getting it home I rubbed it with steel wool to “improve” the finish, I would be considered somewhere between crazy and stupid.

Or at least misguided. 

If I send a sword to Fujishiro for polish and it comes back, and I decide to “improve” the polish through application of uchiko, I am doing the same thing as these other examples. 

Fuhishiro when he hands the sword over to me, has determined with all of his skill and experience and training that the sword is now in as good condition as it can possibly be.

If I disagree with him and think I can improve his work with sandpaper, well… this is again subjective, but I think misguided. If I do not trust him to complete a polish to perfection then I should not be sending it to him to be polished. Otherwise, the job is done and it is as good as it can ever be.


My only goal as a custodian of the sword is to not screw it up. Don’t break it, don’t drop it, don’t mess up the polish, don’t let it get rusty, don’t don’t don’t don’t don’t don’t don’t. There are no “dos” on this list. Just don’ts. I am to conserve it and preserve it and not add my own interpretation onto the sword.

That cannot be done with uchiko because uchiko is constantly abrading the surface. It is ruining Fujishiro’s polish and turning it into some nightmare hybrid of master craftsmanship and home workbench jackassery. It is constantly embedding uchiko in the surface and ruining the look of the sword. It is constantly threatening to ruin a shirasaya and turn it into sandpaper. It is constantly threatening to destroy the sword through use of this ruined shirasaya. 

All of that means the use of uchiko is functioning in the opposite direction to the need to conserve the sword. 

When the sword leaves my custodianship, and someone looks at all of these scratches and crap and surface changes that have happened to the sword during my jackassery, their first feeling is going to be, this is a really nice sword but it is going to look a lot better once it gets a polish.

And the cycle begins anew.


Swords have finite lives. Every polish strips one life away from them. Like with the ocean, nobody quite knows what lurks under the surface. Maybe a mermaid, maybe a shark, maybe a nuclear tipped missile that is going to destroy life as we know it for the sword. We do not want to look under the surface unless it is absolutely necessary. 

Not many people look further down the road from their own stewardship. Or they assume that they will be the ones to restore it and once restored it will stay like this forever. 

But even if you do your best and just conserve it, that will last only until the next guy gets that sword and starts to “improve” it with uchiko. Then the cycle of destruction begins again. 

There is no need to fix a Fujishiro polish and make it better. You do not need to alter Mishina’s polish or any other mukansa polisher. If you do not like their style, do not send it to that polisher. If you cannot live with a good perfect polish as it is because you do not like the style, then don’t buy the sword, there are others. But do not ruin a perfectly fine polish with uchiko because you are going to kill one of the lives of the sword eventually, when that sword changes hands and the next guy decides to reverse your well intentioned “improvements” that ruined a polish.

Undead hands kill polishes from beyond the grave

And remember too that your uchiko jackassery will, 9 times out of 10, last beyond the grave. You may die and that sword may be polished but the well intentioned collector who had it polished did not make a new shirasaya. Or split the old shirasaya. And as a result, that sword after polish will go right back into the sandpaper hell that you created through years of inserting uchiko into the shirasaya. And so you strike beyond the grave to destroy the successor polish over time… and even that guy, not doing any jackassery of his own, eventually destroys the polish having inherited your masterwork and didn’t think to, or wanted to save money on, or for preserving a sayagaki legacy, avoided creating a new shirasaya after polish.

So I Can’t Use Uchiko, What Do I Do?

You use a microfiber cloth. You keep it clean, you keep it put away and hidden from dust. You get a new one every now and then. This with one gentle wipe will soak up and remove any oil from the sword without abrading the surface. It won’t leave any crap behind to ruin the sword or the shirasaya. It will move you away from ca. 1100 AD technology and into the 21st century. It will preserve and conserve the sword.  It is simple, easy and cheap, and very difficult to jackass up.


Below are typical damages made through proper and improper application of shirasaya. I will document each cause and how it affected the sword. Damage may not always be immediately visible because it is always some form of scratching, and as a result may be more highly visible at certain angles. Therefore without a complete and uniform inspection of the sword, it is possible to miss the damage. Over time the damage accumulates and finally becomes obvious at all angles.

The first sword is a Juyo Ichimonji and the owner had an old uchiko ball that has been used forever, probably it is the first one that this owner ever bought. The owner used it consistently on oiled swords by hitting it into the ji of the sword. The ball over time collected oil from the sword. This oil has impregnated the fibers of the ball. On impact with the sword, when uchiko powder has discharged from the ball, it has stuck to the oily fibers of the ball and stayed in place. Thus the ball now has a surface composed of uchiko slurry embedded in the fibers instead of being a clean silk surface. As a result, the fibers themselves are abrasive. Every time the ball strikes the ji with force, it leaves a textured fingerprint of the ball. It is possible to identify swords as having passed through this person’s hands by the fingerprint of the uchiko ball. 


This is another view of the same sword. The owner drags the uchiko ball a little bit sometimes when he strikes the sword with it. Since the fibers themselves are abrasive this leaves telltale drag marks in the ji.


This next sword is Naotsuna. It is a bit polished down so it is even more important to consider the finite lives remaining to it. Unfortunately the owner didn’t really think about that too much as one side shows consistent and hard strikes of an uchiko ball. 

In this case the damage is formed by the first strike discharging so much uchiko that the surface of the ball lifts some of the uchiko up with it and this is repeated on each successive strike. So the surface of the ball is abrasive in a random pattern depending on what the ball picked up. Each strike then abrades the surface in a round pattern with random sub patterns in it. Depending on the angle of the light they may not be visible. 


The overuse of uchiko has also created a linear scratch pattern in the sword. This is visible in the glare around angled light. This is just simply an old polish which has been uchikoed for a long time. Since this sword is a bit polished down already, trying to fix this is probably out of the question now.


This next sword is a Tokubetsu Juyo Soshu sword and it was polished by Fujishiro and owned only by high level, experienced collectors and dealers since the time of its polish.

Even so the ji of the sword showed about six or seven heavy uchiko strikes. In this case they were strikes with drags and created gouges in the ji. Fujishiro’s polish lasted less than 5 years before being ruined. Is the solution to repolish this sword every 5 years to clear out damage from owners using this tool improperly? We can never guarantee that they will use it properly, they never will, and as shown here even proper consistent work will eventually destroy the polish. It’s better to just not touch uchiko.


The next sword is the Nagashige from my site. The polish is in good state and from almost all angles there is no visible issue. There is a burnishing scrub mark in it where the saya has collected some uchiko most likely, and there are very fine linear scratches in it from “proper” application of uchiko. At the current stage these probably will not be noticed at all, but continuing use of uchiko will degrade it into the situation with the Naotsuna above. So it’s important to conserve it as is when it is still in a good state of polish.


The next sword has gomabashi on it and illustrates the drag zones that form at the end of horimono. The drag zones appear darker because they are more reflective (i.e. less hazed) than the areas of the sword that had uchiko application. Though there are no scratches visible on this sword, indicating that the uchiko was very carefully and thoughtfully applied, the drag zones will always form because the horimono is scooping away the uchiko. In this case, the drag zones can be made less evident by using both directions for application of the uchiko, one wipe each way. That will not completely prevent them, but you know what? It’s better to avoid them entirely and use a microfiber cloth. The drag zones are not so evident unless the angle of the light is right, but even so, they are there and show that the polish has been altered through application of uchiko. And any sword with horimono in an older (and good!) polish will show drag zones as long as uchiko has been used. I see these on Tokuju swords in their photos, in books with high level pieces in them, everywhere. 


This next sword is a Soshu sword that shows improper removal of uchiko and likely too much oil in the first place. Slurry has formed and has embedded itself into every tiny variation of the surface. Small kitae ware are jammed full of uchiko. Small corns of uchiko have invaded everywhere on the surface. The net result is distracting as it makes the sword look a bit tired when it is perfectly healthy, because we equate the whiteness with coarseness, and in this case it’s just uchiko. I started flagging them all and then got tired about halfway through. This is maybe just one inch of the blade or something. It needs a bath and careful removal of all of this, and the shirasaya will need to be split and cleaned most likely.


The next shows very clear and very fine grained yamashiro steel, but improper removal of uchiko has left it on the surface of the sword, where it then got into the shirasaya and has formed abrasive corns inside. They have gouged the surface. We can tell the difference between this and over use of uchiko because the gouges are different sizes instead of regular fine scratches. This is because the shirasaya has collected random size patches of uchiko on the inside and where it’s collected larger ones, you get bigger scratches. 



Don’t use uchiko unless it is a sword that needs polish already, and you are not going to be causing any damage to it. It’s for rusty swords, swords that polish is not worth paying for, or for professionals only.

Since there is no way to guarantee that everyone touching a sword with uchiko will apply it perfectly 100% of the time and remove 100% of the abrasive that is applied to the sword, that alone means that any use of uchiko will end up with problems. 

That uchiko is an abrasive and an ongoing modification to a polish is also an issue, because it is implying that the polisher cannot finish his job correctly. In this case, it is more likely that the collector needs to adjust his expectations for what a sword should look like, or simply buy old swords in the state that they appreciate already. Because there are many, many swords already that can be bought with a “broken in” by uchiko look (aka. damage), and we don’t need to add more to this list.

In my situation, I see uchiko damage on the majority of blades that pass through my hands, which indicates to me that it is an out of control tool, an outdated tool, a tool that the masses cannot properly use, and when we have good alternatives to it that are guaranteed to cause no damage, there is no good reason anymore for people to use this as a regular part of sword care.