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Was mono-steel construction more common before kobuse?

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These pics indicate that mono-steel was around koto times though I heard it's harder to make and more expensive which is why the kobuse method gained prevalence during the Sengoku Jidai when they needed to make swords ASAP. I wonder if mono-steel or kobuse is better at maintaining "must not bend, must not break, must cut well." I know there are more complicated lamination methods like soshu kitae but as far as I'm aware none have been confirmed to be made this way. I just know that kobuse is by far the most common, especially by contemporary smiths, along with some being sanmei.



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Its n interesting question James and one that s difficult to answer, not least because different methods were employed over different periods on different types of blade. My understanding, which is largely based on perception rather than hard fact is that earlier work by such smiths as Sanjo Munechika and the Awataguchi smiths were mono construction. As you move in to the middle and later Kamakura period there is more evidence of more complex construction. The main proof of this being the appearance of core steel when a blade is polished down. However Tanto were made from a single piece for much longer. This can be clearly seen where blades which have been greatly reduced by numerous polishes retain the beautiful ji-hada with no evidence of coarser steel appearing. Rightly or wrongly I have always associated the appearance of kobuse construction with the late Bizen and Mino smiths the Muromachi era as you say speeding up production (and lowering cost) in mass production. As a side note I have heard many differing views regarding this construction. One view is that the softer core benefits the blade helping it to absorb shock. A more cynical view, which I tend to share is that this is a marketing hype to try and justify using lower cost material.

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Great thread, and great reply, Paul.


Now, I don’t have the knowledge to answer your question, James but I’ve always read that marugitae was the poorer construction, that the most used method, pre Gendai times was Sanmai and that from Gendai It was Kobuse. I don’t know where and how this was determined (though for modern sources you just have to ask, I guess). I know that for modern Chinese replica, mono steel, unfolded is the best construction as it avoids potential bad welding between layers. However, I’ve also always read that multi layers, several steel construction, added to differential tempering was the best way to ensure both resilience and cutting ability.


How much is myth and how much is fact, as Paul says, can probably only be answered by the users themselves and they aren’t there anymore. Still, would it be surprising that a trade got better and evolved technologically as it progressed in time? And the number of blades still extant from Muromachi (granted, much more were produced) can only be a testimony as to their efficience and resilience.

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Agree, with the exception of the Kobuse method being a poorer construction, cost cutting or time saving (mass production). An outer sheath of premium steel especially the Ha wrapped around a softer core seems just so logical for purpose of robustness and being slightly more work intensive belies it making a process suited to the mass production during the Warring Period as an excuse over a mono-steel method. It may reduce the time needed to homogenize a sufficient quantity of steel pure enough for an entire sword. Time experiments for efficiency need to be done to be absolutely sure though.

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If we have a deeper look into history,  we see that the first goal of iron making was to obtain soft  (wrought) iron. This material was very ductile and thus easy to bring into different shapes, and it could be used for a wide range of tools.

As a by-product of the iron-making process, a bloomery kiln also produces steel. This depends on the position of the KERA (bloom) in relation to the air inlet and the temperature. In the TATARA process, even cast iron is produced which cannot be forged because of its very high carbon content. Anyhow, cast iron can be used in an OROSHIGANE kiln (refining kiln) to produce steel from soft iron.

It seems that the first iron makers in Europe (800 B.C.) could identify steel and were able to separate it from iron as they could not use it at first.  As there was no metallurgical knowledge,  the presence of carbon in steel was not known; they probably thought that there were two different types of iron: hard and soft.

In Japan, iron making was not a technique developed locally in the country, but all knowledge came from China via Korea (as far as I know, sword production in Japan started probably in the 5th century). We may assume that Japanese smiths learned and knew about refining iron to produce a homogeneous material with predictable properties. However, in Europe it is known that the first Celtic sword blades made from iron were likely to bend  in a hard blow and had to be redressed.

It was certainly a second step in history to combine soft iron with hardenable steel to produce a shock-resistant blade with a durable cutting edge, and in Japan this technique was certainly developed further. 

As thrusting weapons like TANTO are not likely to bend in action, they do not need an elaborate inner construction. On the other side, swords require a much more sophisticated structure.

To come back to James' question, it can be said that there is no simple answer, but construction is always related to application - 'structure follows function'.  On the other hand it is safe to say that historically mono-material blades came first, and were later improved by the addition of steel into the weapon or tool. This is backed by many samples from Japan, but also from other iron-using cultures all over the world. The simplest form is the steel edge welded into a tool with an iron body (WARIHA-TETSU or SAN-MAI) as we see it still today in Japanese axes and knives.   

The cementation (or 'case hardening' which is not a correct term) process where carbon penetrates into the surface of an iron body, is a later development. 

Hope that helps a bit.  



SAN MAI blade 1872.jpg

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