Sharp edge

[John John]

Just my opinion and open to different beliefs, the edge of a Katana is best not kept razor sharp. It is tradition to have the edge at the very end of the narrow bevel, but this will most likely cause the edge to fold or chip when using. A very slight second bevel is a good insurance against damage yet still holds a very sharp edge.

[Lewis B]

Smiths from some traditions, particularly during the Koto era, often gave their blades ha-niku, increasing the fullness behind the edge to strengthen the edge and thus reduce the risk of chipping or catastrophic failure. Its often a kantei feature.

[eternal_newbie]

There are anecdotes of samurai gently cutting into mounds of sand with their katanas before a battle to blunt/bevel them sufficiently when facing opponents they knew would be armoured.

[Tcat]

Classic article by Keith Larman on the topic of niku - https://japaneseswordindex.com/niku.htm

[Lewis B]

10 minutes ago, Tcat said:

Classic article by Keith Larman on the topic of niku - https://japaneseswordindex.com/niku.htm

Very nice treatise on the subject. The explanation why a high and wide shinogi was adopted, as found on Kamakura and Nanbokucho era Yamatoden blades, makes a lot of sense. My Senjuin has a lot of niku with a narrow motohaba, effectively reducing drag by minimizing contact surface with the target.

[John John]

It's like a hot chisel with a cold chisel edge.

[ROKUJURO]

6 hours ago, John John said:

.....the edge of a Katana is best not kept razor sharp. It is tradition to have the edge at the very end of the narrow bevel, but this will most likely cause the edge to fold or chip when using. A very slight second bevel is a good insurance against damage yet still holds a very sharp edge.

Ian,

do you suggest that collectors should grind their blades themselves to change the primary cutting bevel? And what makes you believe that the original edge would fail on a blade that is part of a collection and is of course never used? 

[John John]

10 minutes ago, ROKUJURO said:

Ian,

do you suggest that collectors should grind their blades themselves to change the primary cutting bevel? And what makes you believe that the original edge would fail on a blade that is part of a collection and is of course never used? 

I was more so indicating the opposite meaning: do not over-sharpen if the blade is dull. But as you point out, it's not a job for the novice if the blade is of any value. Once again, it is a matter of opinion and a belief according to the experienced user of the cutting edge.

[ROKUJURO]

Ian,

any tampering - polishing or "restoring" - with authentic historic blades is frowned upon here, and any advice for sharpening or dulling those blades is not in line with their preservation which this forum is devoted to.

If you have a Chinese look-alike, you may treat it as you like, but please do not report that here.

[John John]

3 minutes ago, ROKUJURO said:

Ian,

any tampering - polishing or "restoring" - with authentic historic blades is frowned upon here, and any advice for sharpening or dulling those blades is not in line with their preservation which this forum is devoted to.

If you have a Chinese look-alike, you may treat it as you like, but please do not report that here.

Restoration is critical when needed and can be done by an expert if employed. Many fine family blades have been restored, but more have been abused over the centuries by incompetent persons, hence destroying the great beauty that once was. I would never suggest or advise any restoration without consultation with an expert first.

[Scogg]

Expert restoration by a qualified Togishi is perfectly acceptable. In that situation, though, I would defer to the Togishi’s expertise regarding the proper geometry and bevel for that particular blade.

 

I cannot imagine requesting a specific bevel on a traditionally made Nihonto simply because it is supposedly better for cutting. These are objects we study and preserve, not tools we are trying to optimize for modern day performance.

That's how I see it at least.
-Sam

[John John]

38 minutes ago, Scogg said:

Expert restoration by a qualified Togishi is perfectly acceptable. In that situation, though, I would defer to the Togishi’s expertise regarding the proper geometry and bevel for that particular blade.

 

I cannot imagine requesting a specific bevel on a traditionally made Nihonto simply because it is supposedly better for cutting. These are objects we study and preserve, not tools we are trying to optimize for modern day performance.

That's how I see it at least.
-Sam

You make a good point, but a modern day blade of high quality is able to hold a sharper edge. The older blades may have originally had a steeper bevelled edge, and that edge was removed long ago and reformed more than once. Ancient blades become dull with time and use, so the blade becomes narrower every time a new edge is introduced, and that would be for the polisher at any given time to take the liberty and freedom of style to accomplish a desired edge. So if that were done today, it would be no more than a recurring procedure.

[ROKUJURO]

Ian,

I wonder where you got your information from. The theories you are putting forward are not taking into consideration that sword-blade cross-sections changed over the centuries, to an extent following the development of armour. The objective of a competent TOGISHI is not to sharpen a blade in the first place. A good polisher will restore a blade with the same angles and proportions that were intended by the smith who made it. Sharpness comes more or less automatically in this process. 

That is how I understand it.  

[Scogg]

My understanding mirrors Jean’s. The goal of a togishi is to restore a blade as closely as possible to the smith’s original intent and highlight the smith’s workmanship through polishing, not modify its geometry. Inevitably material is lost through polishing, but that does not mean the general form should be altered.

 

If a different bevel were appropriate, I would think it would be adopted as part of the smithing tradition itself, rather than introduced later as a polisher’s alteration. 

 

@John John I’m going to move this to the general section since I think it fits better there. I’m no expert, and maybe we can get some more eyes on the topic in that section.

Best,

-Sam

[John John]

4 hours ago, Scogg said:

My understanding mirrors Jean’s. The goal of a togishi is to restore a blade as closely as possible to the smith’s original intent and highlight the smith’s workmanship through polishing, not modify its geometry. Inevitably material is lost through polishing, but that does not mean the general form should be altered.

 

If a different bevel were appropriate, I would think it would be adopted as part of the smithing tradition itself, rather than introduced later as a polisher’s alteration. 

 

@John John I’m going to move this to the general section since I think it fits better there. I’m no expert, and maybe we can get some more eyes on the topic in that section.

Best,Thanks Sam.

-Sam

 

4 hours ago, Scogg said:

My understanding mirrors Jean’s. The goal of a togishi is to restore a blade as closely as possible to the smith’s original intent and highlight the smith’s workmanship through polishing, not modify its geometry. Inevitably material is lost through polishing, but that does not mean the general form should be altered.

 

If a different bevel were appropriate, I would think it would be adopted as part of the smithing tradition itself, rather than introduced later as a polisher’s alteration. 

 

@John John I’m going to move this to the general section since I think it fits better there. I’m no expert, and maybe we can get some more eyes on the topic in that section.

Best,

-Sam

 

[John John]

5 hours ago, ROKUJURO said:

Ian,

I wonder where you got your information from. The theories you are putting forward are not taking into consideration that sword-blade cross-sections changed over the centuries, to an extent following the development of armour. The objective of a competent TOGISHI is not to sharpen a blade in the first place. A good polisher will restore a blade with the same angles and proportions that were intended by the smith who made it. Sharpness comes more or less automatically in this process. 

That is how I understand it.  

A steeper bevelled edge removes less steel than following the original full bevel, and it removes chips and protects the edge for longer. You would need a strong magnifier to see the change in angle that I am referring to.

[YourBabyBjornBorg]

I think following the original full bevel is required for traditional polishing to work. In a full polishing (and not just a touch-up like Nugui-Naoshi), around 7 kinds of wet stone are used, and every kind of stone must be thoroughly and heavily (with polisher‘s whole bodyweigh on it) applied to the whole sword, so Jigane and Hamon can be clearly seen all over the sword, and any imperfection forces the polisher to go back to the last stone and do it all over again, losing more steel in the process, so following the original full bevel is the best way to save Niku, as opposing to intentially alter the Nikuoki of the sword.

 

I believe "a steeper bevelled edge" is referring to only sharpening the tip of the blade, like a secondary bevel, this is called......Wait, what is it called again? It's the same Japanese word for the act of gently cutting into mounds of sand mentioned above, something 刃 something, but it's more used in Tameshigiri, and is considered harmful and a shortcut because it only sharpens the end of the blade, making it harder and more harmful for the next full polishing.

 

Ah! It's 寝刃合わせ(Netaba-Awase)! Man, that was killing me. So yes, Netaba-Awase can mean both cutting into mounds of sand to get a jigsaw-like blade for cutting, and the act of only sharpening the end of the blade for a secondary bevel, and again, the latter is considered by polishers to be harmful and impolite to the sword, as it ruins Nikuoki and makes it harder to fully polish.

[ROKUJURO]

3 hours ago, John John said:

A steeper bevelled edge removes less steel than following the original full bevel, and it removes chips and protects the edge for longer. You would need a strong magnifier to see the change in angle that I am referring to.

Ian,

while you may be completely correct when talking about modern knives and cutting-edges physics in general, we cannot apply this to authentic Japanese sword blades. We try to keep them as close as possible to their original shape. No "improvements"!

[EricMajo]

Worth adding a nuance: if a blade is actually used for iaido and hasn't seen a fresh edge in years, resharpening has a real practical justification. But most iaido practitioners who move to shinken use modern-made blades for that purpose, not antique art-swords — using a genuine antique nihonto for iaido practice (let alone tameshigiri) is uncommon and really only sensible at a very advanced skill level, given the risk to the blade. For a purely collected/decorative piece, resharpening makes little sense either way.