Sister blades in sandwich style steel construction
Steel construction
Three layer (Sandwich), but special sandwich or oposite sandwich
c = core steel, o = outer steelUsually the core steel is so hard what can become a sharp edge, while the outer steel is softer.
But this time for Gotoba challenge, the core steel is softer to get less risk of cracks in the quenching work, and outer steel is harder to get a bright temper line. But still, this construction has some risk, because the core steel is hard enough to become a sharp edge. It is impossible to make the risk zero, as long as it is a weapon blade. Some of Kiyomaro blades are like this style.
Core steel is folded 15times. It is not very hard, but still hard enough to become a sharp edge by proper hardening work.
Outer steel is folded 9 times, with mix of soft steel pieces and too hard steel piece. It is hard, but the layer is not very compact, because of less foldings. It's OK, since it is not an edge.
The steel block what constructed in the special construction is drawn out to a log. And then, it is cut in four to make four sister blades.
3 blades are for project Gotoba. Challengers made clay designing, heating, and quenching.
And the last one is tempered by kokaji himself
Sister1 under polishing
Sister2 failed
Clay designing
Just after the quenching work : Most of clay popped off in the water.
Rough sketch of the hamon : The hamon is made of large particles, and its pattern is big wave. A crack appeared in the hamon.
Sister3
Polished by the challenger himself.
Sister4
It is tempered by kokaji himself.
