JCC992

After the blades were rough shaped with the sen, they were finish filed to shape. The edges were profiled and the sen marks taken out leaving the surface of the blades with a nice smooth file finish. They were then ready for the application of clay.

The clay is first applied as a light wash using a thin mix put on with a brush. That is dried then ashi lines are applied from the ridge line to the edge. The ashi lines are thin strips of clay that run roughly perpendicular to the edge. The purpose of these lines is not confirmed, but among the reasons given is that it helps to provide stress relief when the blade takes its final curve. They also may help prevent cracks from running length wise on the blade. I suspect that they also may create areas of turbulence during the quench and help create areas of variation in the hamon. They do have a impact on the final character of the hamon and are traditional.

After, the ashi lines are applied a smooth layer of clay is applied to the back of the blade down to a point just below the ridgeline and up from the edge nearly half the width of the blade. For clay we used a high temperature mortar mix from A.P. Greene Industries, called Satanite. It is mixed with distilled water to a smooth consistency and applied with either a rubber spatula as shown here or with a wooden paddle. The final thickness is less than and 1/8 of and inch per side and completely covers the spine of the blade.

The clay was dried by the forge door before the blade is put into the furnace for hardening. Satanite does not air set and will not harden at the heat treating temperatures, but does remain stable and will not flake or spall off during heat treating.

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