Pincheck

I reckon so. The rate at which this oxide layer grows depends on the carbon level of the steel and you can bet that any other impurities or additives will also make a difference. It has to be said that nugui oil usually contains magnetite and other things designed to allow the polisher to darken the steel. Magnetite is just iron oxide and a thin enough layer will behave to same way. So some polishers may add this effect, thus disguising it’s natural development. Since this mechanism could (theoretically) pick out grains or veins in steel if they varied in composition compared to the neighbouring steel, I wonder if that is (one of) the ways in which chikei and maybe jie nie can appear.

Who knows then. I doubt it’s water ingress, I would expect that to flash off in days not years and it would probably provoke isolated rust spots which this has never shown. Micro-abrasion is possible but I doubt it could account for the profound change I’m seeing. It’s literally developed like a photograph, you honestly wouldn’t think it’s the same blade. I doubt it’s dried on camellia oil as I picked it up from the polisher only a few days after he said it was finished, which was a couple of weeks after he said he’d started it. Plus it would have to be like paint to obscure this hada. No, it hasn’t been lying in the sun. There are a few things I can think of that might cause the sort of change I’m seeing. High levels of phosphorus can lead to a layer of iron hydrogen phosphate hydrate forming on the surface of the steel which can be quite dark. That seems unlikely though as tamehagane is famously low in phosphorus. Hematite is formed during the forging process which unavoidably gets folded into the steel producing fine bands of impurities between the welds. Hematite can be anything from grey to black although I do not know if that colour changes in contact with air or moisture or if it will be straw coloured when freshly polished, although I rather think not. Probably the most likely is that high carbon steel is known to change colour on contact with air. A very thin layer of FeO, Fe3O4 and Fe2O3 forms on the surface of steel which causes it to go through several color changes due to the way it reflects light from the top and underside of the layer, in the same way an anti-reflective coating on a glass lens works. At 50nm thick it looks pale yellow, 70nm it’s straw, at 90nm it starts to look more brown, by 100nm it’s a blue gray, finally looking black by the time it gets to 150nm thick. My guess is there is a very thin layer of this stuff at varying thicknesses depending on the grain boundaries in the steel which is picking out and highlight the hada as it grows.

I have a sword of unknown origin. For background, it's mumei, o suriage but still quite long with a 686mm nagasa, it has a noticeably narrow shinogi-ji, little hira niku. No idea what it is or even approximate age, but I like it a lot. Anyway, when I first got it it was in poor shape. It was in gunto mounts of better than average quality with a defaced silver mon. Well out of polish with quite a bit of damage, but something about caught my eye. Whoever the polisher was back in the day, he did a marvellous job as the lines were so crisp you could shave with them. I thought it worth the effort to save so I sent it away for polishing. Prior to the polish, there wasn't much you could say about it other than it had no discernible hada and had a laser straight suguha, but the steel was dark grey, almost black. Immediately post polish, it had no discernible hada and a laser straight suguha but the steel was light straw colored, almost yellow. Fast forward a few years and the steel has gone dark grey again, almost black and now it has a pronounced ko-itame hada, which reminds me of sand, with a few patches of coarser hada and some that even looks like massame hada. It also developed some shirakke utsuri and jie nie. The change is quite remarkable and I was wondering if that is normal? I don't do anything to it, other than the occasional wipe with clove oil (not oil of cloves, the nihonto specific clove scented mineral oil). Pre-polish https://i.ibb.co/G3sBXXRJ/Prea-IMG-0703.jpg https://i.ibb.co/9mnsjgzP/Prea-PICT0013.jpg https://i.ibb.co/yFqh5FGQ/Pre-IMG-0700.jpg Immediately post-polish https://i.ibb.co/NnxW1K6v/Post-IMG-0730.jpg https://i.ibb.co/4wBhSwVx/Post-PICT0036.jpg 3 years later https://i.ibb.co/1f2tjMc3/Full-Length2.jpg https://i.ibb.co/Ng7WJ3fW/IMG-1579.jpg https://i.ibb.co/nMJw1wmS/Devimage14.jpg https://i.ibb.co/0VMX42qN/Devimage20.jpg[ https://i.ibb.co/cKRwtGTF/Dev-IMG-1564c.jpg https://i.ibb.co/39TXw6XM/Dev-IMG-1566.jpg Edit: Unfortunately, it looks like imgbb has compressed all the detail out of the photos which rather ruins this post. Not sure if there's a way to fix that.

I’m not sure if I’ve posted this in the right section but the link below seems a little fishy to me. I’m no expert but the tassel appears to be a company grade officer, not an admiral. It claims the blade is signed by Yoshindo Yoshihara. The only Yoshihara I know of didn’t start making swords until 1965 and this sword is supposed to have been surrendered in 1945. It doesn’t look much like that Yoshindo Yoshihara’s work to me either, looks more like an oil quenched Gunto blade, but maybe there was a ww2 era Yoshihara I don’t know about? What do you guys think? https://www.michaeldlong.com/product/Japanese-ww2-naval-katana-surrendered-by-admiral-fukudome/

I can’t imagine why someone would go to the trouble of carving a kiku mon and then not sign it, but anything is possible. It could be that someone has removed what they thought was a gimei signature and repatinated the nakago. It looks like there might be a slight divot, a different texture and maybe a change in colour where a signature might have been. But that is pure speculation. Whatever it is, I like it.

Thanks guys. I naively thought the outer leaves were lily pads, not sure what the other ones are. Aoi leaves make more sense I suppose. It’s not big, only 75mm across, and correct me if I’m wrong but I was under the impression that a lot of the more functional tsuba were a bit bigger than that, so I’m guessing later (maybe edo) rather than earlier (muromachi or before). But I really do know nothing about tsuba. I got it for a sword I used for Iaido, back when my knees still worked.

I’ve had this tsuba for about 35 years but I know absolutely nothing about it. I was wondering if anyone had any thoughts? It has no markings, it’s the same design on both sides, it’s made of iron with some kind of yellow metal inlay. Any comments would be very much appreciated.

ChatGPT keeps the chat history in its contextual memory so you could feed it information and then ask it questions about what you’ve told it. That history is gone when you start a new chat though. But you can train a custom GPT and save it so other can use it. There are input limits though, I think I read something like 32k tokens, a token is a word fragment like “ing” or “tion”. AI is generally good at things that are incontrovertible mathematical facts, like computer code, and really bad at woolly opinion based things with vague and inconsistent descriptions, like kantei.

After a lot of trial and error (mostly error) I finally got some decent photos of my katana. I have no idea how old it is, or what school it might be, but I like it.

Not that it adds much to the discussion but I also have a showato katana signed Hoshiya Yoshinaga that looks a lot like yours. https://i.ibb.co/9gXS1mM/IMG-1203.jpg https://i.ibb.co/t8QxkRY/IMG-1204.jpg

Thanks, I think. Like I said earlier, people can’t even agree on an approximate age of this one.

Now that I’ve had time to do some research, I think there is a way you could be right on all counts. I showed this sword to a Hizen collector who said he didn’t think it was Hizen Tadayoshi line which threw me off the hizen theory and I had discounted Bungo since I seem to remember them producing a coarse mokume hada and generally having a much wider shinogi ji, neither of which this sword has. But, the hada, hamon, the narrow shinogi ji and some other characteristics do resemble a sword I’ve seen by 1st gen Shizuhiro of the Igo Ishida school, which was an offshoot of Bungo Takada. Shizuhiro signed as Hizen no kami (lord of Hizen province). His work seems to be rare and I’ve only seen two Shizuhiro swords on the net, both had a very tight ko itame hada that looks a lot like mine, one had a laser straight suguha hotsure with no ashi like mine, both had narrow shinogi ji and seemed to follow a kamakura/nanbokucho style sugata, although both slightly different. Shizuhiro worked around the mid to late 1600s. Whether it is Igo Ishida or not, who knows, but it seems like a possibility. So thank you, I appreciate the help.

Well, here are some more photos of it. What do you think? 686mm (27”) nagasa 12mm of very even sori Chu kissaki 33mm, 28.5mm width at machi 21mm width at yokote (26% taper) Kasane across shonogi: 7mm at machi, 5.5mm at yokote Kasane across mune: 6.6mm at machi, 4.9mm at yokote Weight 760g

I would dearly love to date this sword but in this case that seems to be easier said than done. Several knowledgeable people have seen it IRL (including you Paul, you thought Hizen at the time) and so far bids have ranged from early nanbokucho to late edo. It seems like this one is a tough nut to crack because the sugata suggests late kamakura or early nanbokucho, but the hamon is laser straight ko nie suguha hotsure with not much else going on besides some feint sunagashi and one short patch of nijuba. No Ashi, no yo, nothing. It does look to me like it has bucket loads of ji nie and some fine chikei, plus some feint bo utsuri and hakikake on the boshi. But it’s all subtle stuff, nothing outrageous at all. Not what you might expect from a typical koto blade. The ryo chiri bo hi is of a style I’ve only ever seen on one very tired mumei sword thought to be koto and the hamon I’ve only ever seen on an Iga Ishido sword, of kanbun Shinto vintage. Maybe it could be a shinshinto copy but the patina on the nakago looks too deep to be shinshinto and everyone that’s seen it IRL says it’s older than that, so who knows?