OceanoNox

I am not aware of any work on the topic. I think your best bet is to look at contemporary depictions of warriors, particularly in daily life. For instance, 石城日記 (https://kmj.flet.keio.ac.jp/exhibition/2013/04.html#view) is a journal with drawings written by a bushi of the bakumatsu. You can see how he drew his friends and himself. As Tim said, each koryu that deals with the sword will teach how to tie the sageo. For instance, Muso Shinden Ryu and Muso Shinden Jushin Ryu tie it to the right hip, on the lower hakama himo, letting it hang from the kurikata in a curve. Muso Jikiden Eishin Ryu passes it to the back over the saya, then it's brought up to be tied just at the hakama himo in front of the saya. Some will just drop it behind the saya, etc. EDIT: On https://kmj.flet.keio.ac.jp/material/sekijou_diary/sn_04.html, pages 54-55, you can see two fellows with daisho. Although they have haori, you can see the sageo hanging from the back, so it's likely to be just put over the saya, between the body and the saya, and not tied.

You could choose any kanji with a reading close enough to your name. That's what the student helped me with when I joined a calligraphy club, and I had to carve my own signature stamp. For many non-Asians, it can mean quite a few kanji (mine was 4 for the family name, and 3 for the first name).

To comment on alkali use, I had my students make a fairly nice iron oxide layer on steel with NaOH. The recipe is not mine, and it involves a very concentrated solution and electrolysis. We made it to see how protective it would be in a specific gaseous environment (completely unrelated to tsuba). For my own texturing, I have done carving+punches (to make it a bit stone like), or glowing heat in air+acid wash after cooling (posted above). I think I will try a combination of both (carving, heating, acid, then additional texturing as needed) to see if it makes an interesting jigane. My most recent project involved forging a piece of angle iron flat on an old anvil, and already the surface needs very little work: there are lines and a roughness from the forging that give already a lot of character. Jean, it's a pity I cannot join your workshop in July. I hope it is fruitful, and I hope you can share some insights gained from it here sometime.

Literally not the topic here. We just discussed the use of heat with/without oxygen for the "melty" effect of yakite. Nobody talked about the possible effect of particular charcoal for this application. Yes, we are aware of the scientific literature on steel making tradition in Japan (in fact, I referenced a bit in my own posts elsewhere on this forum). Apart from the fact that heating a tsuba for some time, and then putting the oxidized tsuba in acid did yield a similar surface to what's being discussed? Use of acid is specified for patination of iron items (patinate a bit, then clean with some kind of acid, then patinate again), in books on traditional colouring methods in Japan. I am not aware of alkali, except to neutralize prior acid use. Do you have anything in mind?

Back to that and the original idea of masking/etching, do you have a theory, or are there info about the acid used (I always imagined it could be vinegar)? From Ford Hallam's opinion that a lot of the texture was made by chisels and textured hammers (possibly anvils?), I wonder if this kind of mechanical texturing process was not combined with heat to force surface "damage" via oxidation. Then removal of that with acid, finishing touches, and controlled patination. I suppose, aside from asking artisans who make similar stuff (are there any?), and barring the finding of documents detailing the process, we are left with our own experiments to confirm what kind of process could yield similar surfaces to the antique tsuba.

Jean, now my issue is that I used an electric furnace without option to control the atmosphere. I have no idea how it would look like for the same piece heated in a charcoal fire for some time.

I used a piece of "steel", bought from an online shop called Haganeya. I suspect it is SS400, so low-carbon steel. In my case, it is likely coming from non uniform scale growth. You can see in the photo what it looks like. I did the heating prior to anything else. So it messed up the seppa dai, and I was too lazy to shave it smooth... In the end, I soaked the tsuba in warm citric acid for a couple of days.

To add, I have tried to have "fancy" surface by leaving a tsuba in a 1000℃ furnace (electric) in air, for an hour or so. It does result in a surface that seems to have partially melted. It was completely uncontrollable though.

I have tried it, like Ford (hole in the middle of the tsuba, small nail in the hole to hold the guide, and file/scrape away! It's fairly quick, especially if you're not concerned about even spacing. Depth of the lines is another issue, but you can do it with a file or make several passes. Agreeing with Jean here. Scientific analyses of tsuba (either neutron diffraction, or plain hardness measurements) all point out to iron or wrought iron.

I am very surprised it flexes in the air before the impact and in that direction. I expected it would flex at the moment of impact, but it doesn't seem to.

Could it be simply the way he cuts (I am assuming you are talking about the 3:00 mark). From slow motion videos, sometimes it looks like the blade bends downwards, but it's because the blade is more or less thrown before the hands. On the other hand, I have seen a bokuto bend upon strong impact (basically it straightens at the moment of impact before springing back into shape).

It seems that swords become harder in the Edo period. Hamon width and shape (someone told me the issue is with nie or nioi) play a role, I believe, as well as niku, in the durability of the sword. Perhaps more informed people can chime in; it's my understanding that older swords have more niku than later ones, which are both harder and have slimmer edges. (right now, I just found out that Tawara Kuni-ichi's book on scientific studies of nihonto is available on the National Diet Library website, he did measure a few parameters of antique swords). I want to add that there a few schools that do edge to edge, because it's better to chip a sword that can be replaced. From a purely engineering point of view, it depends how it was done. If slow and without heat, probably not much. Rather, considering how kizu and inclusions would be weak points, a reduction in length means a reduction in possible weak points.

https://ja.wikipedia.org/wiki/へし切長谷部 Heshigiri Hasebe is a national treasure on display in the Fukuoka Museum. The story goes that a servant was rude to Oda Nobunaga, who wanted to punish the servant. Said servant fled and hid under some kind of furniture. So Oda cut him by pushing the sword into him, not by swinging. Hence the name "Heshigiri" (cut by pushing).

Ah, indeed, I missed the date for this one. Anything else wrong?

What's wrong about that description? It seems perfectly in line with the current understanding on Japanese armours.