There's that dry wit I was speaking with you about...
Starting this harvest I'm a starving startling artist/
Lyrical arsonist it's arduous spitting this smartest arsenic/
Authentic Katana is only for collection, way too expensive to be used for real! And too rough handling will bend and chip the blade, as in Japanese kitchen knives, since they are made from the same stuff and technique.
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The construction method is totally the same, weld the 2 different metals together and hammer out the shape, just different design for cutting food. Tamahagane, compared to modern steel is pretty much crap. I believe they were like Hitachi SK steel in quality or even worse, just not as pure as the modern white / blue paper steel. Ancient Japan was very poor, they had to fold the poor piece of metal to get the elements well-distributed, and sparks are seen all over the white hot Tamahagane, indication of high impurities.
San-mai or "hard-steel wrapped around soft core" or not, the blade will get bent when being abused too hard( like chopping through very thick and hard objects, like those tests in Cold Steel videos) Traditional Japanese sword is not flexible at all, once bent, it's bent and you will need a master craftsman to fix, it's just more resistant to shattering. The only good thing is the edge retention. Japanese never temper the blades to spring.
Tamahagane is not as legendary as most people think.
sparks are actually not a function of impurities, but in the case of forging, they are due to overheating, and are often an indicator of carbon content. There are numerous papers by PhD metallurgists on sparks and their relation to understanding steel, but for what its worth, its quite easy to tell general steel types based on sparks... i.e. white steel vs blue steel vs v2 vs ginsanko, etc.