Is the katana a good sword shape compared to other single edged swords?

IIRC: Practical for what it was used for; passable sword quality with minimal waste in precious iron, ideal for cutting down unarmored peasantry and as a symbol of station. I'm not sure what the math is on it, but I've had it alleged before the convex curve means a longer cutting surface and better ergonomics while slicing.

Compared to other single edged swords? It's a specialized kind of sword, other single edged swords developed under different circumstances and for different purposes. Their similarity to other foreign sabers indicates something to like.

[spoiler]I just think they're neat.[/spoiler]

not a single good answer, this is why OP should ask actual historians not people who have read a few memes and watched some youtube videos

I thought mine wasn't bad, though I really didn't say anything more than the merely obvious. OP wasn't asking about metallurgy or the specifics of various lamination techniques; the answer of "well it's a curved sword that does curved sword things" doesn't seem entirely bad.

What did you want me to tell him, that it was the perfect fighting weapon of the civilized and invincible superhuman samurai? Or that stupid nignogs couldn't metal and they were all scrap-metal letter openers compared to glorious european meteor swords forged in Odin's clenched buttcheeks?

OP wasn't even asking about length or trends in the sword's design through history.

What gave you the idea I intended to actually answer OP?

For its purpose and context, the katana is a damn near perfect blade. People like to give it shit because of reactionary westabooism, but a well-made katana cuts through targets like nothing else. That said, we also have to remember that the katana was made primarily to be a cavalry weapon, which is one of the main reasons it's curved the way it is; because the samurai were, up until the middle of the Edo period, mounted warriors who used yumi bows and lances.

>which is one of the main reasons it's curved the way it is
the curve was accidental, due to the different carbon-contents of the steel used in its production contracting at different rates when cooled

I may be splitting hairs, but it may be more appropriate to call it incidental rather than accidental. The curve was at the very least not entirely undesirable or surely they would have taken stronger efforts to counteract the warping during the differential heat treatment

The Katana is pretty unique when it comes to construction and blade geometry. Most other swords use a monosteel construction and have uniform hardening, whilst the katana is constructed from different materials and has partial hardening. combined with the slight curvature and the point of balance slightly put forward it makes an exceptional good cutter.
It has its flaws, construction is complicated as fuck, blades are a little more prone to critical damage and due to the optimized cutting ability they don't fare especially well against more point control focused weapons.

Early cavalry blades were indeed more curved than later infantry designed blades.
The more it went, the small the curve of the blade usually got.

It's not really a workable question... What are those "single edged swords"? Most of them aren't going to be designed for the same purpose, you would have to precise one-handed against two-handed, cavalry sword or infantry sword, amount of curve etc.

When the european who were largely using single edged sabres went to japan in the second half of the 19th century, they found the japanese blades ok, overly-sophisticated at best but neither poor nor way better than what they had.

Make of it what you want.

The curvature comes from differential hardening and is intentional. the cutting edge is fully hardened and expands more than the back of the blade. This is done by coating part of the blade with clay and this isolate it from direct contact with the quenching water. It has neither to do with carbon content nor cavalry use, just with cooling different parts of the blade at different speeds. this results in the superior edge hardness of Japanese blades, as the edge is fully hardened and not tempered like in European blades.

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The reason they did this was because Japanese steel was crap, this method puts it on par with other blades.
That doesn't mean it's inferior in some way, it actually is a very innovative solution to the problem of shitty steel, which is only a problem caused by simple geography.

>That said, we also have to remember that the katana was made primarily to be a cavalry weapon
No, the katana was a weapon for the basic footslogger form the very start. It's the tachi that was by and large a cavalry sword, at leats at first.

>or surely they would have taken stronger efforts to counteract the warping during the differential heat treatment
They have no problem making the curvature as deep or shallow as they like. They can do some adjustments post-quench, and if they want more than that they simply forge in a curvature before that then gets added to what the quench brings. Make that a forward curvature for a less curved or outright straight blade.

>construction is complicated as fuck
It varies, but overall and by the standards of old swords? No really I'd say. Adding smaller parts together to make a larger blade was common all over the place, and when you're doing that putting different steels in different places isn't all that much more to worry about. Sure, they ahd some variants with quite a lot of different bits, but most blades are a bit simpler, and there exist the rare few Japanese blades that are just kawagane steel straight through (mostly tanto). Further refining of the metal as it comes from smelting was an absolute necessity for everyone.

>and not tempered like in European blades.
They tempered the edge in Japan as well. Though I guess in some cases it may have been done through residual heat in the spine tempering the edge instead of a separate re-heating step. youtu.be/gxwWf-MfZVk?t=2417 (Though they get one thing wrong, it isn't the second quench that tempers, that rather stops the tempering process at the right moment.)

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No, not really, Japan only has minor iron resources but chemically they are the same thing as everywhere else and technically they are made the same way Europeans would made high quality blades around the year 400. Smelting ore in a bloomery and refining the resulting material into steel by forge welding and folding. What most people do not understand is the different principles in construction. European blades most often have a uniform hardness of 54-57 RC and as a constructing more resemble a spring. A Japanese blade has a differential hardening with a soft core and up to 62-65 RC on the edge. The blade itself is under stress and the blade construction follows different principles to allow for this. This is a pretty unique Japanese thing and comes with great benefits and the same amount of drawbacks.

>The reason they did this was because Japanese steel was crap
It was the iron that wasn't fantastic not the steel. Steel was fine.

>It varies, but overall and by the standards of old swords? No
So you say hand forging folded steel by by a single master is not complicated as fuck compared to manufacturing blades from blanks and use high level of work division like they did in Europe, Ottoman empire or Indo-Persia?

>The reason they did this was because Japanese steel was crap
How and according to what source? The inclusions (that just about everyone used to have in amounts demanding you deal with them) are beating into behaving by the folding. The chemical composition? If you have a look at the sulphur and phosphorus amounts in mediafire.com/file/37hsh4pa2hslsia/Study_of_Microstructures_on_Cross_Section_of_Nihonto.pdf/file you'll find that they're far below the acceptable limits even for current day carbon steel (compare with azom.com/article.aspx?ArticleID=6570 ) and even the unrefined tamahagane in mediafire.com/file/a14r4ojo85cu7e0/Tamahagane_Production%2C_Control_of_Slag.pdf/file goes from somewhat below to well below.
The bit about geography makes me suspect that you've been served some variation on the old tale that iron sand makes poor metal because... reasons? It has sand in the name? Some such. In reality it's simply an eroded magnetite ore (which makes the guy I once saw who claimed it was used because Japan's volcanic bedrock was too young for rock ores to have had time to form somewhat amusing). It can at times have a bit lower iron content than other ores, but that does nothing for the quality of the final metal, it simply lower the yield from smelting a bit. There's also a bit extra titanium in the iron sands, which changes the slag chemistry so you can run the furnace at a lower temperature, saving fuel (see the second article above). This is why Japan kept using iron sand ores even after they found and experimented with un-eroded rock ores.

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mass repliers should be banned on sight.

>European blades most often have a uniform hardness of 54-57 RC
One made today, sure. But if you start hardness testing old European swords you can find a huge range of hardness values within a single blade, the graph here I ripped form MyArmoury once upon a time IIRC, but I recommend getting hold of William's "The Sword and the Crucible" for a more in-depth look at things.
For a quick explanation, many old European swords weren't just medium to high carbon steel straight through (it's only really around the end of the middle ages that that takes off) and even once we do see that shift these steels are simply very shallow hardening. As such even if you do give a blade a full heat and quench the hardness can end up falling off quite quickly as we go beneath the surface.

Ah, so you meant "the task undertaken by this one, specific craftsman", and not how complex the blade itself ends up being with varying layers, bits and so on. I very much think of the latter here.

That said, I think it's easy to exaggerate things here. The Japanese blade smith, with aid from a few apprentices, would fold the steel, forge and file the blade blank, harden, and then maybe do a bit of further rough shaping by filing or so. And that's for high end work. Then it's off to another guy for final shaping, sharpening, and however much polish is called for (the current day art level polish not being something that even existed until the late 19th century, see Takaiwa et.al, The Art of Japanese Sword Polishing).
Whereas in Europe, well, a bit of folding would probably tend to remain for the blade smith to do, he then has to make that blank you mentioned, and perhaps we then hand over hardening to someone else before it's off to the shaper/sharpener/polisher. There doesn't seem to be a world of difference, though the modern day focus on it s a work of a (along with Japanese laws severely limiting the production rates) could probably make it seem so.

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The main problem is that we tend to compare 17th Japanese construction with 16th century Europe (Longswords etc.) while a more appropriate comparison featuring similar production methods would be possible if we took a look at 5th century Europe.

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I wouldn't call it accidental, as the amount of curvature can be varied, the production method does however make the creation of straight blades (perfect reverse curve prior to hardening) and double edged hardened blades extremely difficult.

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If we're talking workflow then to a decent degree yes I think. If we're looking at just the blade though then a surprising amount of the not-homogenous-steel bit sticks around at least until the late 19th century or so. As just another example of technology sticking around here, bog iron was used for commercial metal making here in Sweden until the 1930s, and charcoal fired smelting furnaces still saw some use up until around WW2.

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The katana is just a sabre with a slight curve, while the tach has a more exaggerated curve.

What made the Japanese sword so great was the tamahagane steel, its spongy, not good for making a sword the traditional way, but great for folding. On top of that it was differentially hardened. The edge was hard while the back was soft so it could cut but also bend under pressure.

>not good for making a sword the traditional way
What kind of traditional sword making are you referring to?

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In most places folding is the traditional way. You're not getting sword-suitable steel out of any old furnace, and as such basically everyone folded. It's only today with much more advanced metallurgy (and hot strip milling to do basically the same job as the folding once did) that we can skip that. The historical exception are crucible steels, where you replace the folding step with a melting and solidification step (as the crucible steels didn't come that way from smelting), which removes at leats most of the need for folding. And it wasn't just for swords either that we folded, here's a part of a door hinge, probably 18th century, showing a layered structure that should indicate significant folding.

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so that explains why old metal things are so "grainy" and with lines in thm

Smiths actually look for old worthless metal objects to turn into pattern welded stuff because the old steel is "dirty" enough to self "lubricate" during folding.
You don't need to constantly use borax or sand to cover the stuff in order to keep the planes from corroding to the point of no longer welding properly.

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Not folding would be the traditional way. Japan got all its iron from Korea until folding methods made their way to Japan in like the 6th century. Japanese iron was considered garbage in Japan before then, kings would even be buried with piles of Korean iron ingots in the past.

Depends if you're in a outright fight like a formal duel kind of thing, or if it's a random occurrence. I'd probably go for an axe and just tell people I'm a dumb hick. It'll split a wig, there isn't pretending there is anything fancy about it. In a random thing, I'd honestly expect a glancing hit from an axe to work better than a sword. A sword hit would be really brutal, an axe hit would probably be a bit more fatal. You just don't want to go at someone with an axe and fail. They live by the sword and it isn't double edged, they're not going to fall on it if things go wrong.

That's an odd way to look at tradition, because Japan basically didn't have any metalworking tradition back in the Kofun period. They just had some imported techniques, and smiths, with a total production of very little. The burial tombs are filled with imported items, and odds are pretty good that's what most swords and such were at the time.