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Carbon content is related to utsuri no doubt of that, a 0.45% C can't produce utsuri, while over 0.7% can. Anyway I shared enough of my personal experience and Japanese swordsmiths experience, the readers can decide what they think works better. The topic is already exhaust for me

I don't see any mention to utsuri or hamon in the article, I don't know how can be relative to the utsuri topic. This process shows how grain size changes during cycles of normalizing and annealing. The grain size doesn't affect the appearance on the ji, it might influence the hamon in some degree, but depends on how the yakiire is performed

I would say not a common way to make utsuri, also not much reliable, but it still can work, since the principle is the same, different temperatures when cooling rapidly

Midare utsuri Bo utsuri

Exactly, any form of forging and hardening is a thermocycling, but what he stated in his first post is a series of process of heating and cooling with application of clay prior to the yakiire that would lead to the creation of utsuri. I just want to know where this information comes from and how it should look like when it's done. Because so far the only way I know to create utsuri is by temperature control during yakiire. It's not something I claim, it's been done by several swordsmiths, not only Japanese

Of course any form of hardening is a thermocycling, because it changes the composition of the metal through heating and rapid cooling, what I mean is that specific process you described in your first post. Can you provide an example of blade made that way and how you know that process has been used on it?

I have close to 1TB in my library, you gonna need to be more specific on what you want me to show you. Meanwhile can you show me some examples of what you assume is an utsuri created by thermal cycling?

I already showed several examples, but apparently they're not utsuri? I'm not trying to fight or being petty, just I'm sharing my first hand experience, and those who say I'm wrong provided no evidence of what they're saying.

I'd say with the same steel a blade with utsuri has more resilience, so can withstand hits without breaking, more than a blade without. Sharpness is due the hamon so not directly influenced by utsuri. I agree with Kiita saying that first times could had been accidentally created by trying to avoid heating the blade too much and for too long time, but then became a feature when they figured out it worked better on the battlefield

Kapp never mentioned cycling in the book, it's heating at different temperatures at the time of yakiire, which is the same I said in my first post. So if nobody did that in modern times, how do you know it was made that way back then?

Just to understand, is this utsuri to you?

So where are the blades that we know for sure are made with this method?

Yes but doesn't create hamon nor utsuri from what I know, do you have any actual example of hamon and utsuri create by this method?

same blade as the same picture, not a second hamon. I know how to look at utsuri another blade from same swordsmith, is this "real" utsuri? Who made this theory? Do you have any evidence or experiment about this process? This sounds an overly complicated process for someone who wants to reduce the risk of mistakes during hardening, not to mention this might give some extra internal stress. This would not be easy even with modern day tools.

I never said he did master the old koto masters utsuri, and anyway those are just two examples that I actually own. This topic isn't about who made the best utsuri, but how utsuri is made

The smith is Kei'un Naohiro

In that case is because the whole area is not covered in clay, so the hamon is created naturally by the slightly uneven temperature and the steam that occurs when plunged in the water, since the temperature decreases in uniform way from edge to spine the utsuri would tend to have same shape of hamon. Of course there are some specific cases that can also be made with clay, I assume Yoshii School used clay but managed to have a shadow utsuri, maybe just making deep ashi with clay

I have in my collection swords from Kamakura, Nanbokucho,Muromachi, Edo and modern with utsuri, so the utsuri never disappeared, just "fell out of fashion" cause other styles became more popular. I also have some experience in making knives with modern steel in Japanese style, and i succesfully made utsuri in several. First of all there are many kinds of utsuri, some i have no idea of how they're formed (tho i have some theories), but i'm gonna talk about what i found out by experience first hand and watching a Japanese swordsmith working that actually makes utsuri in most of his blades. The utsuri i made is the most common style of utsuri is the one found in many Bizen blades (of course also in many others, but just to understand what i'm talking about). The way to create that utsuri is actually "simple", you heat up the edge of the blade only to the temperature of quench, so the rest of the blade will have transitional temperatures which will turn out in different cristalline structures in the metal and different hardness, resulting in a different appearence once polished. This can be done with or without clay or with clay only on the shinogi-ji to help control the temperature.

That's a stylized rain dragon, common in Kaga zogan pieces

I have one even earlier than Edo period, Tensho koshirae from Muromachi period, still with the original blade inside. All lacquered black, even the original seppa have traces.

Thank you for entrusting me with this restoration, at first it looked quite serious but after removing the oxidation I found that the original patina underneath was pretty much untouched by corrosion, also the zogan was rock solid in position, a testament to the quality of the work from this tsubashi. So I just had to make a new patina on the brass and stabilize the iron patina. It was a pleasure bringing back to life this excellent work.

Small groves are filed to ensure more grip and prevent it to slip towards the center of the nakago ana

Actually it is listed in Sesko's Sworsdmiths book MOTOSHIGE (元重), Genkō (元享, 1321-1324), Mino – “Motoshige” (元重), “Rokurōzaemon no Jō Motoshige” (六郎左衛門尉元重), first name Rokurōzaemon (六郎左衛門), it is said that he moved once from Kyūshū to Yamato to join there the Senju´in school, in the second year of Genkō (1322) he moved to Seki and acted their as one ancestor of the Seki smiths, kiri-yaasurime, no authentic zaimei blades are extant by him, it is also said that he was the same smith as Motoshige (基重) I followed the auction as i thought it's an interesting blade to own, but that's way above my means

I agree with paint, more than lacquer. Patina doesn't flake off. An alternative would be fire scale, but the tsuba doesn't look it's been damaged by fire so that's unlikely.

Sekigane are simply held by friction, many times an inlet is filed on the tsuba to make them hold more firmly, then filed to the exact size of the nakago. The umegane of hitsu ana are cut and filed to the precise size needed to lock in the hole and decorated, then tapped in. Usually they're not a single piece but two thin plates with pitch between them which helps to stick even more.