This blade was forged and underwent yaki-ire at the museum forge. It began as a pre-1960s (integral) cultivator tine used by a farmer a generation or more ago. It is a sunnobi (overlength) tanto in the forest pattern, charcoal-forged and water quenched with clay, a satoyama style outdoor knife that has the foundation of the Japanese sword.
The starting point as a lengthwise half of a pre-1960s (integral) cultivator tine.
After the tine has been straightened the sunobe (preform) is forged with all tapers and proportions in place.
During the hizukuri stage the peaked spine is forged in first, followed by the bevels.
After the final heat for the forging stage the steel is heated evenly to normalize, removing any stresses remaining from forging.
After filing the notches and the spine some additional adjustment is necessary along the bevels.
The bevels are filed slightly along the edge to clean them up before hardening.
After a final round of normalizing again, heating to an even temperature and then cooling slowly in air.
Preparing the mixture of charcoal, clay, stone powder, and water.
The clay mixture will control the cooling rate of the main part of the blade during yaki-ire.
After yaki-ire–the exposed edge has cooled quickly and become very hard, the blade has gained some curvature.
The area protected by the clay layer cools about half a second slower as it hits the water and remains in a tough, ductile state.
The clay is cleaned off, the hardness checked, and the blade is tempered slightly over the flames.
