Sister blades in kobuse style steel construction
The outer steel (edge steel) is not too sensitive for Gotoba challengers, since it is made of mix forging. It means a little less risk of hamon cracks in the quenching work, than Kokaji's usual work. Of course, it is hard enough as it could be a sharp edge (getting a bright hamon) by proper tempering.
Core steel is forged out. It is made of rather soft steel folded 12 times.
Outer steel
Selecting hard pieces from the tamahagane "O'warishita" what are steel nuggets with random qualities and sizes. So it is a kind of mix forging in natural way.
In the picture below, the outer steel is on the work of 6 times folding.
It is forged out after 13 times folding.
And then, the core steel and the outer steel are constructed to a steel log with kobuse style construction. And made several sister blades out of the steel bar.
Kobuse sisters in project Gotoba
1
2
Just after quenching
3
Clay designing
Just after quenching
4
Clay designing
Just after quenching
5, by kokaji himself => new sword7
Just after quenching
