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Swords, Cutting and Military History

Bringing a cutting edge back to life

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Many people have been asking for information on polishing, sharpening (or otherwise re-edging) a sword used in modern test-cutting practice.  While this seems a simple request, it’s a very wide open and technical topic.  To bring a dull blade back to life, we may be looking at three entirely different kinds of “sharpening”, each with their own level of technical difficulty, skill requirements and equipment.  We’ll look at the three major classification of “sharpening” :

Re-edging: Using a simple leather stropper or sharpening steel to re-align the blade edge

Sharpening:  Using a combination of tools or whetstones to remove material from — and reshape — the cutting bevel and final edge of a blade

Polishing or Restoring:  An extensive removal of any rust or tarnished areas of a blade by literally  wearing away — and potentially reshaping — the entire surface area of sword, including sharpening the cutting edge.

In this article, we’re going to look at various ways to bring a blade back to life, from the easiest — requiring no particular skill — on up to actual polishing / resurfacing of a blade, for which a practitioner will need a great deal of training, equipment and practice to be successful.

 

Re-edging and stropping

As I’ve discussed in other articles, most blades used in cutting start to become dull not because the cutting edge is being worn off, but because the fine edge thickness (the width of the actual cutting edge;  where “sharp” = approximately 3/1000th inch or 90 microns width or less) is actually folding over with the impact of cutting.

Folded edge

Edge exhibiting folding and breaks photo by Kasrak

This folding creates an extremely wide edge thickness, making it more difficult to cut through targets, thus requiring more force be used, which folds the edge even more. The easiest method for restoring / re-edging an undamaged blade — that is, one without major nicks or breaks in the cutting edge — is to re-align the folded edge so it is straight and narrow again.

This can be done by stropping the blade on a section of leather which has had a fine abrasive rubbed on it, similar to the technique used by old-time barbers to re-edge straight razors.  The blade edge is held down on the leather, then is pushed across the stopper away from the cutting edge.  The rough leather surface, combined with the fine abrasive, pulls any folded edges back into alignment;  the abrasive also helps wear off any rough surfaces or burrs which may form as the edge is pulled back into shape.  For more information on the mechanics of edge sharpness and stropping, see my Razor Edged series of articles.

 

Sharpening

Edge angleEventually, any sword used in practical cutting will develop small edge nicks, cracks or signs of chipping, as material is worn away or the edge fractures through repeated stressing.  The only way to repair this damage is to use a stone to wear away the damaged material, exposing fresh metal for a new edge.

This must be done very, very carefully;  the practitioner will need to wear away the edge bevel (the final angle of the blade from the blade width to the cutting edge) without changing the angle of the bevel.

This angle determines the final cutting edge width, guided by the overall shape of the blade and the hardness of the steel.  If the angle is made too acute (sharp), it can result in such a thin edge thickness that the steel folds over or chip at the lightest impact.  Too obtuse (low) an angle, and the cutting edge thickness will be so wide it’s effectively dull.  Most swords have a edge bevel of approximately 30 degrees, though this can be set differently by the smith or manufacturer if blade shape etc. require it.

You can, through the use of the leather strop technique with a heavy grit abrasive, easily remove small nicks and chips.  However, larger nicks will require much more of the steel to be worn away to create a fresh edge.  An good introductory article on sharpening an edged weapon for Do-It-Yourselfers is Sword Buyer’s Guide’s How To Sharpen a Sword.  Some of their important tips for beginners include:

DON’’T attempt to sharpen swords that are antiques; – leave that to the experts, otherwise you will almost certainly destroy their value.

 

DON’’T use normal power tools to sharpen swords unless you REALLY know what you are doing. For a start, it’s extremely dangerous. Secondly, the friction can heat up the blade, ruining the swords temper and heat treatment, and it’s all too easy to lose the swords geometry.

 

DO be very careful and patient when sharpening swords. More accidents occur when performing sword maintenance than at any other time, so make sure that you are paying 100% attention to what you are doing and eliminate outside distractions.

While various articles and experts recommend the use of different tools,  in general you’ll be going through at least three phases in sharpening your blade edge:

  1. Roughing the edge
  2. Polishing the edge
  3. Finishing the edge bevel

 

1. Roughing the Edge

By “roughing”, I’m referring to quickly wearing away quite a bit of your edge material, to expose fresh steel.  Many practitioners recommend the use of a metal file for quick removal of this material, while others suggest the use of heavy grit waterstones (400 to 600 grit) for more careful roughing.  There are several web forums with discussion and debate of sharpening techniques and tools, including Sword Forum International’s discussion: Sharpening European Swords for Cutting as well as MyArmoury.com’s in-depth discussion of How to Sharpen a Sword. You might also want to look at Nihonzashii’s Japanese Sword Polishing guide

The major point here is to ensure Roughing an edge with a fileyou keep the sword’s edge bevel at the correct angle while roughing, and rough equally along the length of the blade.  For beginners, note you must rough the entire blade length on both sides, and not just the spots where the damage has occurred.  Not doing this will result in dips and wavers in your final blade edge, which will become points of weakness for further chipping, in not actually causing points where stress fracturing can take place.

 

2. Polishing the Edge

Once the edge has been roughed at the correct angle, you can use an oil or water-stone to polish the edge, removing the roughness and bringing the edge bevel to a clean, sharp point.  Again, there is discussion amongst experts as to what grit stone should be used;  most suggest at least 800 grit material.  Your goal here is to hold the blade at the correct angle for the edge bevel;  make smooth, even strokes equally along the length of the edge, on both sides, always stroking in the same direction.  Never use a back-and-forth or circular motion, which can create uneven surfaces and weaken the final edge.

Some experts suggest making the strokes by holding the edge bevel down, pointed away from you, then pushing the blade outward.  Others recommend holding the edge bevel down facing towards you, and then pushing the blade away.  The difference between these two techniques seems to be in how they wear away material;  in the first (edge outward) technique, material is worn away from the edge towards the back of the blade;  this leaves a clear but potentially rough final edge thickness, as the grit tears out parts of the steel.   Proponents of this method say the resulting edge normally doesn’t need any final treatment.

The second (edge inwards) technique pulls the material of the blade toward the cutting edge, which can result in a tiny “burr” remaining on the final cutting edge.  Those who promote the use of this style of polishing say they can then progressively use smaller-and-smaller grit whetstones to remove the burr  and create-and-align the final cutting edge thickness.  This, they feel, gives them much finer control over the edge thickness, allowing them to work with the qualities of the steel,  resulting in a much sharper cutting edge.

Which technique you choose depends on your needs, interest and sword culture background.

 

3. Finishing the edge bevel

Once you have polished the bevel and created a final cutting edge, you will still find that the angle where the edge bevel joins the body of the blade will be very sharply defined, and likely very rough and uneven.  A simple way of finishing this rough join is to use 400 grit oiled paper to smooth or “blend”  the join into a visibly seamless whole.

Those who wish the join to be a very sharply defined line will need to use finer grit whetstones to smooth the roughness and create the line.  This is best done by holding the blade at the correct angle (when working on the edge bevel side of the join;  flat when working on the blade body side) and evenly stroking the blade down the stone.

This is a very delicate operation.  One point I can’t amplify enough is stop and check your work frequently, every two or three strokes.   Not doing so risks removing too much material, accidentally altering the line of the join and ruining the look of the blade, not to mention risking weakening it.  I would seriously recommend practicing on cheap knives and blades before attempting the creation of a sharp-line finish.

 

Polishing or Restoring a blade

This is the most difficult of jobs. To totally remove all surfaces of a blade (and thereby removing rust, tarnish, pits, nicks or other damage) while at the same time maintaining and enhancing a blade’s lines, appearance and sharpness, without removing so much material that you weaken or damage the blade itself, or change it’s shape and geometry so much that the optimum edge thickness can no longer be attained.

Both in Eastern and Western cultures, sword makers and polishing and restoration experts spend years learning their craft.  For antique blades, conservation (maintaining a blade in its historic condition) is considered a better option than restoration (bringing a blade up to modern standards, using modern materials).

I cannot recommend that anyone other than an expert should attempt a full polishing or restoration of an older blade.  For modern cutting blades, regular maintenance and upkeep to prevent rusting or tarnishing is a much better option, particularly when combined with regular stropping and the very rare edge sharpening (only when absolutely needed, preferably performed by someone with experience).

However, the full polishing of a blade is a very interesting thing to watch.  To begin with, there are a wide variety of polishing stones used in the process, both natural and synthetics.  Japanese expert polishers (Togishi)  prefer natural stones, some very rare and expensive, particularly for the fine finishing polish.

A quick reference to the main (not all) stones used in polishing reveals six levels of stones are normally used:

  • Bisui  – Used to take off heavy rust and return the blade to its original shape. It is very coarse and if poorly used can ruin a blade.
  • Kaisei – It refines the shape and takes off the marks of the bisui.
  • Chûnagura – A relatively hard stone of fine grain, it is used to remove kaisei marks.
  • Komanagura – Finer version of chûnagura, taken from the center of a depoist. It removes chûnagura scores.
  • Hato – Very hard stone used to bring out the hamon (tempered area near the edge). It takes great skill to use, as both the blade and stone are very hard.   It can easily take hours just to complete the ha (edge).
  • Jito – The hardest stone, it is used to bring out the Jihada (surface grain pattern). If improperly used it will ruin days of work, and requires the highest level of skill to use.

The following video provides a quick visual introduction to Japanese polishing stones and their qualities:

 

 

To give a better idea of what a polisher does, the next video — by a Canadian polisher — gives graphic examples of how a Japanese-style polisher works, and what each level of polishing  achieves

 

 

This next, much longer and much more technically detailed, video has a professional polisher working on a blade while lecturers (both Japanese and English speaking) comment on the process:

 

 

 

Sources

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