A dull blade is annoying and can even be dangerous but many people are far too scared to reprofile, retouch or even simply cosmetically polish a blade that is isn't performing as it should simply because they're worried they'll destroy it in the process. Sometimes this fear is warranted, in fact there are too many instances where an amateur albeit with perfectly good intentions, has ruined an expensive sword purely because they didn't realise the sort of skill that was required in the work. Theres a reason after all that professional togishi are paid highly. Any person that is paid a lump sum, then an additional amount per inch of work must be at least fairly highly skilled and by that I mean they must have "many years of practice skilled", not "has made a kitchen knife sharp skilled".
For professionals, the polishing and sharpening process is one and the same thing, requiring handfuls of different skills and even more tools and materials. The sort of attention to detail that goes into the work produced by Togishi is the sort that is usually attributed to people who suffer from Obssessive compulsive disorders (meant as a compliment) which is why most people who casually pick up a blade and attempt to replicate the masterpieces they've seen on the internet do more damage than good.
I say most people of course, not all and thats because when you start the process you need to know what you want to get out of it. It's very easy to say that you shouldn't sharpen your blades and you should simply pay the money and get someone who has done it for years to have a look at it but this isn't always the case. if you're looking at anything valuable and by that I mean historic or authenticly produced nihonto then you should never touch it yourself. always go pro. If the blade is precious to you, then you should think about how difficult it will be to produce a finish that you would be happy with and then double that difficulty in your head before committing to it. If it is a functional or relatively inexpensive blade that you're looking to work on, then I say maybe it's worth it for the experience and the satisfaction that comes from what is essentially maintaining your tools. A lot of production line katana can end up in a state of polish that is uninspiring, but if you're careful you can change that. As long as you've got the time, effort and patience.
This article will go over bringing your sword to increasingly high levels of polish but one thing to bear in mind is that historically, katana were not brought to a mirror finish. The shinogi-ji was indeed polished and burnished to make a slick shiny surface, but the hira and the ha were done using different stones that would not only produce a more matt finish but also add to or acentuate existing colours in the steel and the hamon. This is something that I am totally unskilled in and I wont be including anything on it here for that reason. Neither will I be going into the counter polish found on the kissaki as I'm sure that once you've gotten the gist of what I'm going over here, something like a counter polish should be easy enough for you to implement yourself. The only things I will be showing you are how to get a functional mirror finish and if you go at it carefully, a blisteringly sharp edge.
Before you run to get your tools though, there are a number of things you should know. Normally I'd just skim over them and get to the nitty gritty and of course you _can_ skip ahead if you want but I feel that more knowledge of not only what you're trying to do but also everything else surrounding it leads to a better understanding of the process. It pays to know what your're not trying to do as well as what you are. Let's start with the different types of blade profile that you can find not only on katana but on any type of blade.
Hollow Ground Blades
Hollow ground knives have a concave cross section. They look like metal has been removed with a circular wheel from a metal bar and thats because 95% of the time, thats exactly how theyre made. A blade blank is taken to the grinder and metal is removed until you are left with a supporting spine that drops away rapidly to the edge of the knife.
Sometimes this concave shape is very pronounced such as with the much screen written "cutthroat razor" and sometimes it is a lot less noticeable like on a normal EDC lock knife. The idea is to have a tough main body of metal that as quickly as possible comes down to an edge that can be finished off with minimal steel removal on final sharpening.
The convex blade cross section is what is used most often on katana. If you were to look at a slice of blade, the actual cutting surfaces lead from the spine to the edge in a outwardly rounded fashion that resembles an appleseed.
This is called Niku or blade meat when referring to japanese style blades and the extra material makes the blade far more robust than other grinds. This also means that it is much more able to take the sort of high velocity pounding that a sword ends up going through when in use. The appearance in this kind of edge can mislead you into thinking it isn't that sharp but let me warn you, done properly there is far less sacrifice in sharpness than you would think. convex blade cross section is what is used most often on katana. If you were to look at a slice of blade, the actual cutting surfaces lead from the spine to the edge in a outwardly rounded fashion that resembles an appleseed.
Flat Grind Blades
Blades done with a flat grind are the easiest to sharpen and they sit in the middle of hollow grind and convex types having enough metal to lead to the cutting surface and no more / no less. Scandinavian knife makers use this sort of edge a lot and for that reason when referring to knives rather than swords it is foten used called a 'skandi' grind.
Katana wise, although there are definitely examples that have a true flat grind, I have found that the majority have a rounded edge right at the end. This means that they are partly convex, its just less prounounced than the more traditional full niku approach.
Regardless of what blade profile you have, when you're talking about penknives, most have a secondary bevel. This means that right at the edge, at what looks like the cutting edge before you look closely, you will find a sharp angular change at about 20 degrees. This is the edge that actually does the work. The main pronounced 'edge' is simply thinning the metal from the supporting spine of the blade to this real edge. 20 degrees of course sounds like a very acute angle but we're only talking about the angular change on one half of the blade. The working angle or what is correctly called the 'included angle' would be 40 degrees or the sum of both on either side of the edge. Secondary bevels, because of the relatively heavy change in angle, provide more supporting metal all the way to the business edge of the blade and are therefore more durable whilst the sudden reduction in the amount of supporting metal makes the blade thinner and helps to facilitate better cutting. It's a best of both worlds approach that works well for small knives but is truly awful for swords.
Ok, so you've got a real quick understanding of the main types of edge. There are others of course found on chisel style edges or sashimi knives but for katana there are really only two types, The fuller niku and the No niku style. When sharpening a katana unless something has gone horribly wrong, the geometry has been set the way it has for good reason. When you sharpen a sword you are trying to follow the existing shape of the blade and not cut new lines into it, in fact it's the dismissing of this principle that leads to the much maligned penknife style edge on katana. The edge should lead all the way from the top surface of the blade, be that the shinogi or the Mune depending on what geometry you have, and lead down in a smooth line to the Ha. Swords with no niku, a true flat edge are the easiest to sharpen because of the fact that is is a cinch to lay a flat blade on a flat stone and sharpen away. It is the swords with niku that require a little more attention.
If you just want to get the low down on what you need to do, watch this video which will show a blade being touched up.
In order to get started you're going to need the primary sharpening tool and the best thing for this would be a collection of water stones. They offer the best finish and the least frustration but they are often relatively expensive. When I picked one up I paid about £30 for a dual stone with 1000 grit on one side and 3000 on the other. For general purpose tidying up, nick removal and polish I highly reccomend this middle grade type of stone.
What I used before I managed to get my hands on a water stone was wet and dry sandpaper. I simply spray glued the wet and dry to a flat ceramic surface and used that. It's a less expensive method but the paper wears away fast and you have to keep removing the used and replacing it with new which can get tedious in the long run. However, this is a method that I've used before, it works fine and it's easier to change the grit by simply using a higher grade paper. I still use wet and dry at the lower grits to clean up horrible looking blades before I move up to higher polishes.
The grit of the paper or stone that you're going to start with depends on the level of damage or use on the blade you're intending to work on. A blade with a lot of damage or a piss poor polish means that you're going to have to start at a lower grit value, probably 400-800. Do not think that you can just polish away with a 4000 grit stone until all the dents are gone and you end up with a mirror polish, it simply doesnt work that way. If the blade is in a state then you'll have to work your way up to the higher grits, so trust me when I say it is far quicker to do that than to try and slog it out with a high grit stone or papers. If the blade is in fairly good condition and just needs a tidy up then start with 1000 and go from there. Foundation work is essential if you plan to make your blade beautiful so it's well worth it. Along with stones/papers you'll also need a flat and firm surface, a cloth, a container of water and knowledge of where you keep the band aids.
Table to show the conversion between US and Japanese grits
Waterstones are not supposed to be used dry (obviously) so if you're using stones then you'll need to soak the ones you intend to use for about half an hour before you do so. Wet and dry simply needs to be splashed with water as soon as you see it getting dry. If you find you're leaving out of place or unusually deep scratches on your blade at any point throughout the polishing process, it could well be that youre not using enough water.
A good point that was raised by a friend recently that I should of mentioned, a tip really. Adding Bicarbonate of Soda to the water that you use will raise the pH of the water and help you to avoid rust issues. This shouldn't even be an issue as after you sharpen, you'll be drying and cleaning your blade right? right? But still, its an interesting tip and can only help.
Placing the blade down on the polishing surface, push gently on the Ha edge of the blade. A sword with niku will rock forward slightly onto the cutting surface and this is where we will be maintaining pressure at the beginning of each stroke. If the blade has no niku, then you can push on any area of the blade as the whole surface will be engaged no matter what. I find that being as I am right handed, my right hand grips the bottom of the sword and my left is the hand that applies pressure to the ha. Move the sword upwards and to the left and then back again, repeating in even strokes about 10-12 inches in length. How long you make the strokes is entirely up to you and the main thing is that they are kept consistent and you do not feel like you are over stretching yourself. Make sure that as you come to the end of the backward stroke, the angle remains constant as any sharp changes may mean that the blade takes small lumps out of the stone or paper. This often happens at the kissaki where the least movement in your right hand will cause the greatest change in angle at the tip.
On a large piece of paper glued to a ceramic stone, the angle that you have the blade turned to on the horizontal plane doesnt matter so much, but on the raised and narrow surface of a sharpening stone it pays to keep the blade at an angle between 30 and 45 degrees so that more of the blade surface is in contact with the stone at any one time. You should also make sure that the fingers of your left hand are over the middle point of the stroke and that the strokes are not too long. The reason for this is that the pressure on either end of the sword will cause it to bow slightly if you are not careful and cause uneven contact with the stone and also uneven areas of pressure as the surface area decreases.
A blade with niku will have to be rocked very slightly towards the back of the blade throughout these strokes in order to accomodate the curvature of the cutting surface. This is something that you will have to feel for yourself as every blade is different but a tip is to rock it slowly as far as you feel it needs to go and then turn the blade over to see how far the residue from the stone or the paper have gone and where the scratches stop. You will find that you need to rock the blade a great deal less than you would of imagined and whilst doing this, you need to try to avoid rocking the blade past the shinogi or you will round the definition right off of it. Although functionally this makes no real difference, aesthetically it will. I told you blades with no niku were easier right?
Diagram to show the area that is polished on a blade with shinogi,
in this case also with bo-hi and a blade with no shinogi.
If you listen to the noise as well as watching the movement you will be able to tell if you are making consistent scratches on the surface of the blade. Remember that polishing is simply making smaller and smaller scratches until they are too small to be noticeable ;) Polish this area of the blade for 100 forward and backward strokes before moving down to the next. All throughout this, if you feel like the stone is getting dry then rewet it, if you want to look at the finish of the blade so far, thats fine, simply wipe the residue off. Remember though that with wet and dry, every time you wipe off the residue, you are losing some of the sharpening powder stuck to the paper. replacing the paper when it looks worn is key with wet and dry.
Diagram showing the two sharpening movements made to create the X shape scuffs. of course once one side is done, the other should have no evidence of the previous direction.
Once you hit the bottom of the blade, wipe it clean and inspect it. The scratches should be uniform in direction and finish and you could find that some areas may need to be reworked a little. Don't worry about the size of the scratches at this point, simply keep them as uniform as you can. Once you're happy with this step you can move onto the next which is simply the same thing but in the opposite direction, the two directions of scratches if put together making an 'X' shape on the surface of the blade. What we're doing is obliterating the last series of scratches so they are completely replaced with new ones.
You should do this step in the same manner as the last, stopping if needed to check on your progress, taking your time and aiming for consistency. I must confess that I never finish a blade in one sitting. Not ever. This sort of attention that this requires is deceptively large and if you feel yourself not paying attention or if your arms ache then you need to stop or you'll end up messing it up. I normally do one direction in one grit, all the way down the blade and then I take a break, sometimes for an hour or so and sometimes for a day. I make sure I do some work on it every day and by the end of the week I'll have made progress that I'm happy with. Slow and steady wins the race!
The final part of using this grit abrasive is to make longitudinal scratches along the entire length of the blade. This needs to be done carefully of course and the main problem you will encounter will be at the start and the stop of your stroke where the blade will wobble and leave unsightly wiggly polishing lines. Dont worry about this, the more of these longitudinal strokes you do, the more practice you have, the straighter they'll become. These long strokes along the blade not only do the same job of removing the previous scratches but also because they are all in one long line, lend a much more shiny finish than the multitude of diagonal ones you've been doing prior to this. This isn't so important if you're shifting up to a higher grit and going through it all again, but if this is your final polish, the results are quite prominent.
Stop! Common sense time. Don't forget to thoroughly wipe down your blade, and powder and oil it as you would normally after use. The most annoying thing that happens to you the day after you've been hard at work polishing, could be finding patches of rust all over your blade. Its common sense but dont forget ok? and no matter how tired you are after all this, don't be lazy. Be meticulous.
The simplicity of this technique, is quite astounding when you've seen the results. It just takes time and to work your way up through the grits until you arrive at the stage you want to stop at. I stop at 3000 simply because its good enough and thats the highest stone I have at the moment. It gives a pretty good mirror finish but if you look closely enough then you can see the tiny scratches still on the surface. If I wanted to I could simply repeat the process above but with a 4000, 5000 or even higher grit and maybe one day I will but like I said, it depends on what you want personally. The finish I put on my blades is probably a lot more than I need but I'm a sucker for aesthetics and I like pretty. Whilst we're on the subject of pretty, if you want to acid etch your blades to bring out the hamon more then a mirror finish is where you need to start. If you start with a crappy sub par polish, you'll get worse results when you etch. If you put crap in, you'll get crap out so even if you're looking to use lemon juice or ferric chloride or whatever to enhance a sword, putting in the time and effort to make sure you're starting with the best that you can manage will ensure that the end result is a product of this.
This is the basis of Polishing or sharpening a katana. Remember that both of these things are the same when you're talking about the japanese sword. You're working from a low grit or coarse abrasive to a higher grit or finer abrasive, slowly removing the marks left by the previous process until you arrive at your wonderful shiny destination.
I hope this cleared up the basics for you and as always when working on your swords, be careful.