The quench happens in the dark. Sato Haruto pulls the blade from the charcoal when its colour matches the evening sky in late autumn — about 820 °C.
Clay on the spine
Before the fire, the spine is painted with clay. In the water the uncovered edge cools in a second and freezes hard; the spine, under its clay, cools slowly and stays tough. The line between the two is the hamon.
Listening
A good quench has a sound: a short, high hiss, then quiet. A crack is a blade lost. Haruto has lost four in fourteen years and remembers each of them.
