a Japanese sword specialist, and 2

2. There’s always a lot of discussion about real and ‘fake’ tamahagane. So the question of course : can tamahagane produced outside of Japan (by either a kera oshi tatara or zuku-oshi tatara ) still get the label ‘real tamahagane’ ? After all, we tend to forget that the process of producing tamahagane was introduced by the Chinese (and the Korean?).
This is a rather complex question and subject to one’s point of view. In the metallurgical sense, you could say ‘yes, that all steel produced from the same raw materials of iron (Fe) and carbon (C), using the kera-oshi method or zuku-oshi method produces a form of ‘Japanese-type steel’ for sword production even outside Japan.
However, even inside Japan, we have to begin by defining what is ‘real tamahagane’? Is the locally produced tamahagane of the Kamakura period the same as Edo period tamahagane when centralized smelting took place and steel was shipped along the main roads? Is kera-oshi real tamahagane, or is decarburized zuku-oshi the real steel? Are Shinto era blades made from nanban-tetsu not real Japanese swords? Even today, not all smiths use tamahagane made at the Nitto-ho tatara in Shimane, and many of the ones that do add their own special ingredients trying to emulate a distinctive jigane of a particular smith or school.
Additionally, just as it can be argued that the differences in locally gathered raw materials used for the jigane of the different traditions within goka-den can be distinguished in the hues and textures in a completed blade, a difference can be seen in both the manufacturing methods and the steel itself on non-Japanese made blades. This is not a new discovery by any means, it is said that there are distinguishable factors between continental (Chinese and Korean) made chokuto and domestic chokuto of Japan’s Ancient and early Heian periods that are kept in the Shosoin imperial repository, Nara. Both China and Korea were rich in iron ore, but as it was expensive for Japan to import ore, it resulted in iron and steel production techniques using sand-iron flourishing in Japan. It is undeniable that the steel technology came from China and Korea, but once steel and sword making took off in Japan it began to immediately develop its own characteristics culminating in the introduction of the distinctive curve into the blade.
However, rather than just judging the raw materials alone, we must look at the characteristics of a completed blade as it is not only the jigane that separates Japanese made blades from their non-Japanese counterparts. Swordsmiths in Japan do not just produced a blade with a curve in it and call it a katana or a tachi. The Japanese swordsmith is also something of a connoisseur. He must also study sugata and understand the different shapes of the various periods, and the subtle difference in the sugata of the school that he is aiming for. All smiths in Japan are aiming for a specific school or tradition, and are not just making ‘generic’ Japanese style swords. I think that just as importantly as researching jigane, to be successful, ‘Japanese style bladesmiths’ should also be studying other aspects such as sugata, the related activities produced in a hamon, and should focus their work by aiming at the workmanship of a specific school in a specific era.