The Moment of Yakiire quenching. Amazing transformation during Katana making.

[@ForgeDuLys]

What actually impresses me is how even the temperature is, across such a long blade. That's tricky to do. Your explanations were really good, but i would add one more detail : the curvature of the sword is slightly delayed, because martensite (the hardened crystal form of steel) only forms at lower temperatures (about 180C). This means as long as the water boils, the steel doesn't really expand into the martensite, so it adds some delay before the curving. That's also why when quenching blades in hot oil, you can actually hammer them straight and bend them for a few seconds, as the blade still isn't cold enough to harden (but the quench still collapsed the austenite)

[@clintonm2357]

This is really interesting. I am an American blacksmith and I practice traditional European smithing. I make smaller tools, horseshoes, and blades, so I have not cooled that much metal at one time ever. The structural changes are immense and the stress that would put on the metal is incredible; the creators of these blades must be experts at their craft to not crack half the blades they make. I dropped a hammer yesterday after hardening it and 4 pounds of steel shattered like glass. I was very sad. It would be depressing to have stress cracks in a beautiful sword before you can temper it; to see one explode would be disheartening indeed.

[@Peekingduck]

Just a quick interjection if you don't mind. What you call the "blade part" is called the "cutting edge" in English. The blade would be the whole metal structure from the Nakago to the Boshi. Love your channel so I subbed.

[@rozniyusof2859]

I wonder if this is how Kenshin's reverse edged sword happened. The sword curved forward, but somehow didn't curve back.

[@ravenblackwing7888]

Yes!!!! I've been wondering about that for years! Tho i don't think that's it because the geometry would be completely different at the point

[@Theorof]

I saw the very accurate explanation and had to subscribe immediately. Thank you for your really great video.

[@samurai-tavern]

Hi Stephen, thank you for dropping by and subscribing to our channel :) we are very happy to hear about that! Please let us know if there is any particular topic that you would like to know more :)

[@richardsalim4103]

I have a question, is this the same method used when making katana and tachi in Kamakura era? Because I see the difference between an old katana / tachi from late Edo period vs Kamakura is the bend point are very different and it might be affecting the cutting efficiency, the Kamakura period years 1100-1300, the bend point/curve was start after the handle part ( after tsuba ) so its looked way more curve d than the other katana/tachi, and the Edo period katana curve point start from the 1/4 -1/2 - 3/4 part of the blade. Thanks. Forgive me for my terrible English

[@MovieFactory]

the swords we saw in the video were demonstration pieces. usually the sword already has some sort of curvature before yakiire. for example, if you want to have a straight sword, you would forge the blade with an inversed curve. if you want a more extreme curve near the handle, you forge it in before yakiire

[@samurai-tavern]

Hi ChardS! Thanks for dropping by and I am really happy to know that you know a lot about Katana. as replied by movie factory ( thank you for explaining! ), the Katana is made at different angle in order to achieve the final angle. I met a sword smith and he told us that it is really difficult to make a Tachi. due to large curve, there are high risk of having cracks on the blade during yakiire.

[@Artemis_x98]

Wonderful informative video! ありがとう

[@mattsimmons6717]

thank you very much, I quenched a katana using the clay method a few days ago and was in disbelief at the curve when it came out! Thank you for explaining in detail on why this process happens! Unrelated to yakiire however, I understand there are many different forms of hamon (gunome, notare etc.) is there a specific method to getting each individual one or is it all down to the relationship between steel, fire and water? As well as this, I have taken notice of different blade cross profiles such as soshu kitae (created supposedly by masamune). From my understanding, this is created by forge welding different carbon percentage steels together. Is this correct or not?

[@samurai-tavern]

Thank you very much for your comments too! What an exciting thing you are trying. To quench a katana by yourself sounds so interesting. I hope I will have the chance to do it myself too. Most of the time I get the information from books or other sources and examine the theory with small scale experiment. I might not be able to provide you the best answer but let me try my best to answer your questions. To make a different hamon pattern, there are specific ways of putting clay for creating each hamon pattern. Of course, what you mentioned is said to be very important. If you are interested in clay patterns, I will make a video about that. Moreover, there is a special case, where the quenching katana was done without clay, which is called Hadaka Yaki. For the cross profile, your understanding is correct. Single to several steels with different carbon contents were used to increase the functionality. Also, a welding pattern is important for hamon pattern, for example, so-called honsanmai can make a Kinsuji at the border of different steels. I hope these information would at least help a little for your Katana forging. Please feel free to share your on hands experience or new findings from Katana forging. I will be so excited to hear more about that!

[@mattsimmons6717]

@@samurai-tavern thank you! Your are very knowledgeable in the subject, that clears up my understanding nicely! I will be sure to share any new findings I make!

[@samurai-tavern]

it’s my pleasure! all the best for your Katana forging and stay tune to our next video :)

[@airwatching2]

this video is: 1) extremely interesting 2) really well done -> congrats and thank you for posting! Question: how do they make straight blade sword? (Ninjato?)

[@samurai-tavern]

Hi Ale, thank you so much for the encouraging words! In order to make a straight blade sword, the steel is made curving downward before Yakiire. During the Yakiire, the back of sword will curve upward and the end product will become a straight sword.

[@newchannel1231]

The birth of Katana moment

[@icegds18]

So that's how I get the curve into my katanas?

[@jeremyhannay1967]

How many types of harmon are there ?

[@joesmith6199]

Thank you ! i am not a good enough blacksmith to make a katana. But i am interested in the warm water quench and clay covered blade method.

[@bmxriderforlife1234]

The katana is such a beautiful sword. I like other designs too, but the unique aspects of the katana allow for some very interesting things in the modern age. Howard clark for example. Martensite edge with a bainitic spine. Then modern lamination methods and old methods tweaked to modern materials. I've figured out 2 ways to accomplish the Howard Clark heat treatment on a specific steel. One is much harder but more traditional. However the differential cooling rate in the clay and some other traditional Japanese methods using clay but not necessarily in the way everyone thinks of is how I figured it out. It really is a shame some of the more unique methods of production in katana are slowly being lost. If Japan would allow smith's to make some use of modern materials it might help. Allow art swords and modern material swords only for registered practictioners with stricter rules. I mean. Gassan sadatoshi is like one of the only smith's left really able to reproduce a certain type of hamon that requires not claying the blade. I rarely ever see anyone fully paint the blade in clay anymore to produce hamon. Thin wash on the edge adds surface area to help with more even heating, the thin layer helps cool the edge down faster but at a controlled rate helping prevent cracking due to almost a 2 stage quench. Thin edge wash cracks off after curvature forms and the spine coat keeps heat in the blade so the spine can convert to soft pearlite. Japanese crucible steel for altering carbon content, made in a tatara furnace. Namban tetsu blades using foreign steels to alter steel conposition further. The whole potential hizen wootz/Indian or middle eastern crucible steel theory. I don't personally believe it's wootz but Indian crucible steel or iron is possible easily.

[@davidbielski3484]

I was about to heat up and unbend the tip of a knife. I was going to quench it with a wet paper towel but was wondering on which side to do that so it doesn't go back to being bent as I did. @_@ Now I'm really confused

[@Somegoy]

I just finished watching Ruroni Kenshin since I was a child. Based on how this works, a reverse edged sword like his would not look the way it does because of that principle right? If it were made in the traditional Japanese way. Or would they just make it traditionally and sharpen and polish the opposite side?

[@samurai-tavern]

Thank you very much for the comment. I’m happy to hear that you watched Ruroni Kenshin, because it is one of the thing which I want to recommend others to get interested in Japanese culture. Let me think about the Sakabato… I think, one of the best solution to make Sakabato is to make a sword which is greatly curved toward blade side, before Yakiire process. If the blade part is extended after Yakiire, the shape of the sword still looks Sakabato. The resultant sakabato has sharp mune blade and blade without sharp edge. I think the important point is ,if you use the same steel as you use in making katana, the steel without Yakiire cannot be sharpen no matter how much you try to sharp and polish it, because the material is too soft.

[@lrforgelaguna8918]

@@samurai-tavern i think sakabato was use the same as the katana, the Mune part of sakabato was the substitute edge of the katana and the Ha part of the sakabato was the mune on the normal sword in short you'll defeat your opponent using the Blunt part of the sword which was the Mune in reverse side As a bladesmith on the japanese style blades on the yaki ire process you are definitely right initial shape of sakabato is important before yaki ire to sustain it's shape as the sakabato after quenching. If it has shallow sori before yaki ire it will like a normal katana after yaki ire with kanmuri otoshi zukuri style kissaki downward

[@kisho2679]

why were earlier swords originally still stright (like more ancient chinese swords)?

[@samurai-tavern]

Thank you for the comment. ありがとうございます。 I think that is because these old swords were made for the purpose of stabbing. This is just my opinion from my experience. Cutting something in the battle with swords puts a lot of burden on the swords. For example, Japanese swords always bend toward blade direction at the moment when the sword hit on tatami or bamboo then recovers immediately. Thus, the material should be hard and also ductile otherwise it will easily break. Until the method of purifying better steel was invented, the ancient people just couldn’t make a sword for the purpose of cutting.

[@andychang3567]

I really like this test it's amazing doesn't it good luck and all the best to you

[@samurai-tavern]

thank you and I’m glad that you find this interesting! please stay tune for our next video ;)

[@touken5422]

Japanese swords are beautiful!

[@samurai-tavern]

Thank you for the comment! I think so too.

[@shinoobsoman9269]

informative 🙏🙏👍👍

[@hoangvananhhao2083]

Tôi rất thích những mẫu kiếm Nhật họ có phương pháp rèn thật tuyệt giá nó quá cao nên tôi chỉ biết ngắm 🇯🇵 😊

[@OwlonYggdrasill]

The clay attached to the blade dramatically speeds up the cooling-down process. The clay is necessary to obtain the desired crystal structure.

[@24934637]

The purpose of the clay is to SLOW the cooling process on the spine of the blade. By doing that, the edge cools really fast and becomes really hard martinsitic steel, yet the spine becomes a softer and more flexible perlite. This gives a sword with an amazing cutting edge, but it's not so brittle all the way through that it's in risk of cracking during use. Fascinating process!

[@maurobaraldi5606]

Molto interessante grazie