Asymmetric blade geometry? what's the reasoning?

[terminus]

I noticed some katanas and tachis have asymmetric blade geometries. Especially with modern made katanas that have horimonos. Here are 2 examples: 

http://world.seiyudo.com/product/ka-080420/
http://world.seiyudo.com/product/ka-070620/

Is there a practical reason for this? or is it purely aesthetic? or an utsushi of some famous blade of the past? 

[Ken-Hawaii]

Tony, I'm sure you're aware that it's extremely difficult to get mirror images on omote & ura. The examples you show are far in the opposite direction. I've seen a few with intentional asymmetry, but honestly don't recall their jidai. I doubt that there are many older Koto blades that went that route, but someone like Jussi or Ray has probably seen a wider range.

[PNSSHOGUN]

Utsushi of the famous Sadamune sword if memory serves me correctly. Echizen Yasutsugu made many of these in the Shinto period as well. 

[Yasaka Azuma]

  On 8/17/2020 at 8:42 AM, terminus said:

Is there a practical reason for this? or is it purely aesthetic? or an utsushi of some famous blade of the past? 

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This is pass on secondhand information.
“Kata-kiriha Zukuri is a shape that was popular during the 14th century , but there are mechanical reasons for this.
Looking at the cross section of the sword, the blade angle on the side of Shinogi Zukuri is small and that of Kiriha Zukuri is larger. If you cut an object with this, the resistance of Kiriha Zukuri is greater, so the cutting edge goes to Shinogi Zukuri.
On the other hand, the sword is held by the right hand, but when it is cut, the blade edge faces left. The force that the cutting edge tries to move to the left side and the force that the cutting edge tries to move to the right cancel each other out, and a straight cut can be made. "

 

http://www7b.biglobe.ne.jp/~osaru/kagaku.htm#tsukurikominokouka

 

× kiriha zukuri → 〇 hira zukuri ?
× shinogi zukuri → 〇 kiriha zukuri ?
The author wrote so, so I transcribed it as the original text.

 

[Bazza]

Hmmm - should "kiriha zukuri side" be "hira zukuri side" and "shinogi zukuri side" be "kata shinogi side"?????

 

BaZZa

(OTTOHH)

[BIG]

Thank's Yasaka san, for your ongoing help. You are an enrichment for the board. Keep on going ...

 

Best

[Yasaka Azuma]

Thank you, Peter san. Much knowledge is shared in Japan, but not all are well proven. I introduced a hypothesis that seems plausible.

 

The author of the site that provided the link wrote his profile like this:
"In the spring of 2006, I suddenly lost my eyesight. I became blind, but I want Japanese swords to be known to as many people as possible. I hope it will be of some use to those who are interested."

 

BaZZa san. Please make up for a little confusion and unclear understanding of terms, and I want to ask for forgiveness with my weird English.

 

[Jacques]

Kata-kihira zukuri originated in the late Kamakura jidai.  🙂

[Bazza]

Yasaka san wrote:

> BaZZa san. Please make up for a little confusion and unclear understanding of terms, and I want to ask for forgiveness with my weird English.

 

Yasaka san and all, please forgive my confusion - I'm old and often put my keyboard into gear before engaging my brain, in other words I thought without thinking!!  Even having an asymmetric katana with shinogi tsukuri/kata shinogi tsukuri I still get confused...  Here is my sword:

 

 

BaZZa.

[waljamada]

Don't have anything to add of depth to this but I find the asymmetry of those blades absolutely beautiful.  I personally find a little asymmetry amongst symmetry draws attention to the human hand/mind within the symmetry.  Like seeing a painting in logic or something. 

 

My examples are just aesthetically assymetrical.  One or both of which the horimono added much later.

 

BaZZa, if you ever want to sell that blade please think of me. =|:^)

 

 

[Yasaka Azuma]

Both are great work! I heard that "Katakiri ha-dukuri" is difficult to heat-treat, and that high technology is necessary to finish it without breaking "hamon".