Theoretical calculations on uncovering tachi original length

[Jussi Ekholm]

Now that is bit hefty topic line and I do not really have a standing theory ready for it, nor perfectly accurate formula for calculations. However I have done some measuring in old school way from books and done my own reasoning and thinking. A recent post by Arnaud made me remember what I had tried to do a while ago for few smiths.

 

As many forum members might know ōdachi are the most interesting thing for me alongside big naginata and when I go to Japan those are pretty much the things I seek to look at shrines, museums etc. They are however unfortunately very rare. Of course many of them were shortened into regular sized blades later on. However that brings me to the second problem, there are just huge amounts of long ō-suriage mumei katana attributed to some of the top smiths (and to other smiths as well). In overall so many of them that it will leave me scratching my head. Some massive ōdachi and massive naginata/nagamaki were definately used, however I would dare to believe they were not ordinary weapons that were common to encounter.

 

This is not in any way really accurate data, so do not take it as the truth. However it will give some insight on what I personally feel. For some old tachi it is relatively easy to try to figure out the original length, for some it is much more difficult. For this data I needed to have relatively specific data in order to do the calculations, and of course I do have pictures or oshigata of each and every sword. Now of course for best results I would take pictures of every sword, then put the picture collage to computer and scale it counting pixel to match real life size. I have done this type of thing for naginata in past and it takes quite a bit of time. Someone or AI might succeed in it much faster but sometimes doing stuff like that is fun.

 

I only could of course use signed tachi for this data (I counted in partially signed though if they filled the other criteria). Then I must have the nakago length measurement for the item (this is because many pictures are not 100% in scale in books so I needed to calculate the actual measurements I took) I did measure the gap from munemachi to start of the signature for each ubu sword to be a reference point. There were of course few outliers but I believe smiths signed relatively often in similar placement, and the data would also correlate with this. I also tried to look the signature in relation to ana but I must confess it was getting bit too complicated for me, so as I was not looking that deeply into this I did not have time for everything. Then tried to use logical applying on suriage swords to determine the possible original length. While not perfectly accurate I did get very similar results with my personal method than is listed for few swords by Japanese experts.

 

I did select Tomomitsu and Kanemitsu basically as I like them so much. Rai Kunimitsu was just something I was curious about as there are so many swords (signed and mumei) for Rai Kunimitsu.

 

First up is Tomomitsu there are the 2 ubu ōdachi, and I had only 5 suriage tachi that fill the criteria. As can be seen in graph they weren't ōdachi sized originally.

 

 

Then for Kanemitsu the first entry is the famous ōdachi Ō-Kanemitsu. In my eyes it was originally slightly bigger than it currently is, my estimate was pretty much the same I have seen by experts in books, amazing sword that I hope to see it at TNM some year. The second ubu is the magnificent JūBū tachi at Fukuyama Museum of Art, tiny bit short of being an ōdachi. As I have not yet seen Ō-Kanemitsu this is so far my favorite Kanemitsu. For Kanemitsu there were 17 other suriage swords and only 1 of them came close to being an ōdachi but it didn't really pass as it was tiny bit short. Lots of very large amazing tachi though.

 

 

For Rai Kunimitsu there was actually one suriage tachi that was still very long, and by my calculations and observations would have been originally c. 95 cm ōdachi. This is the National Treasure that is held in Kyushu National Museum, I was around 1 cm of the expert length estimate so while not perfect it gets rather close. Other than that one, all were just long tachi that of course many of them were really awesome.

 

 

This doesn't really give any definitive answers and for myself it just maybe raises more and more questions.  I hope someone finds this interesting.

[Pincheck]

That’s very interesting work Jussi. I did something similar to try and figure out if a dimensional analysis of a sword could in any way be correlated to the approximate age. You hear a lot of people say koto sword were slim and graceful, and that Shinto swords were big and powerful and I wanted to know if there was any truth to that. So I tabulated the dimensions of about 200 swords and plotted various dimensions against age. This is arguably a slightly dubious idea with huge error bars, but what else do you do?

 

My method of estimating ubu length on a suriage sword was to just measure the distance between the first and last ana (usually from the photos) and say that was how much it had been shortened by. It’s probably not very accurate as ana could be placed anywhere and there’s no guarantee that the last one is the original one. But again, what else do you do? Same with age, for mumei swords the estimated age could be out by a century or more. But what else do you do?

 

I looked at nagassa (estimated ubu and extant), sori, kasane, mihaba, all plotted against age. The data came mostly from the web, notably Aoi Art’s comprehensive back catalogue of swords, but other sources as well. 200 swords isn’t many but it takes ages to trawl through it all, and frankly, I got bored of doing it. I can post the plots if anyone is interested. I thought the results were interesting, but in no way guaranteed to be accurate. It is what it is, and all that.

Edited March 4 by Pincheck