Rayhan

Modern steel does not require the process that producess Utsuri as stated in my previous post.

Im getting on my flight. Gents and ladies please think how these process(s) relate tonthe creation of a blade over weeks and months and not from hours or minutes. Sayonara. Ps: for those in Japan now the NBTHK is showing Kiyomaro (excellent examples and not so excellent but all Juyo) it is good to see what experts mean when they say excellent Kiyomaro and not so excellent. Masahide and Naotane also. The Tokyo National Museum is showing Soshu and Bizen (also Bitchu) in all it's glory, go see. Not to mention the other sword specific museums in Nagoya and such.

This is now an amazing example, what we should be wishing to see here is how the clay was placed in various intervals of heating. If only we had that time machine Darcy spoke of so often

So, back to this. @Rivkinthermocycling yes. Please stop putting the cart before the horse. We do not need to speak of Yaki-ire at all when we speak of Utsuri. The development of a blade has its stages and if the smith uses thermocycling (annealing is a process that is involved also but not mutually exclusive) https://knifesteelnerds.com/2021/08/28/how-to-thermal-cycle-knife-steel/ I know knife steel nerds is not a scientific journal but this article helps. If we imagine the process where we are changing the structure of the steel as we go along all the way till Yaki-ire then we can build the visual base for utsuri. @C0Di am not fortunate enough to see Utsuri being produced in real life today, being produced infront of my eyes to say, however, if you have this information please share it here so we can all benefit. I can say that i have an Ichimonji blade and Aoe that both have wonderful Utsuri and will share that when i am close to them again after my travels.

Please give me a moment im busy with this

@C0Dshall we begin with Midare Utsuri from your photographic database please? Perhaps then you can present some very strong examples of Choji Utsuri. Later we can try Bo Utsuri if you can please? I look forward to seeing these

All Utsuri and all Nihonto involve some level of thermocycling, sorry @C0D

Generally if you have modern steel then utsuri is just for decoration rather than function. It will appear in a different, more flamboyant manner. Modern steel does not require this for serious function. @C0Dyou have an excellent visual library, can we begin one step at a time from your library please?

@C0Di think the glass is full. But that is ok. @Matsunokiyou raise wonderful questions. The fact that we should admit cycling happens at every part of the manufacturing process intentional or not is to be kept in mind. The original billets will have their presentation, after amalgimation their presenation will change, after further cycling you will see another change and so on and so on till Yaki-ire when the final form is determined. Remember that there are many forms of Utsuri as mentioned by other members, some intentional and some by trial and discovery. We should move to specific Utsuri then, perhaps @C0Dcan begin by showing specific examples and we can the discuss at what point these were probably made. Every Koto school that produced utsuri or smith had their own process remmeber. But it is for all intensive purposes a method of preserving the steels quality, reducing stress and the utsusri effect is a bi product of that methodology.

Sorry, but thermocyling was done before or in cases after the hamon shape was created or decided. The article by Kapp speaks of exactly that, cycling varied temperatures. It is a feat tentamount to mythical magic if done by eye and not using spophisticated sensory equipment like we have today. I think once you read up on the many varying ways thermocycling can be done and many types of cycling it will make more sense. Koto blades were not made for art only.

This process is used widely in any manufacturing process today. When we make the turbine fans for aircraft we use thermocycling to reduce the stress and evenly distribute the hardening of the turbofans. All lessons learned form long long ago. It also takes a great deal of time to accomplish and you see the structure of the metals change. Anyway just my 2 cents, you can research thermocycling and understand the process and what the reults yeild. Thermocling reduces stress and does not amplify stress, depending on the result we want to create.

It has been a very long time since i had an inkling to comment on the board but since i am in Japan and saw some amazing Nihonto i just dropped by and saw this very interesting topic. Utsuri is a result of the process of thermocycling the steel in different intervals befor yaki-ire. Koto smiths could not afford to make mistakes with their steel. Tamahagane was not in abundance (still isn't) and so thermocycling was used as a way to reduce any risk of issues when quenching. What we must do is look at the direct meaning of Utsuri (to change, to transition) those who own Koi will also understand Utsuri and its meaning. The swords were clay coated in cases and put through thermocycling many times before being quenched. New clay is applied at various intervals, removed and reapplied. This takes time and precission. This produces varying hardness at mm dissipation throught the koto blades. In the later Edo period swords were made in different styles and made in more flamboyance with an emphasis on hamon and the Shinogi was not really part of the same outer jacket of the sword overall so this process was cut back. This also made production of blades faster (no doubt the lessons of cutting corners in the Muromachi period). And so those smiths that reproduced Utsuri in the Edo period and now are following an extensive, time consuming process when making their blades.