yes, the different crystallisation patterns from the softer spine down to the harder edge show as different colouring. the indians were quite good at differential heat treatment. and still are. nepali kami that forge khukuris heat their blades to the right red colour (by experience) then quench just the working part of the edge with a tea kettle full of boiling water. the residual heat in the spine tempers the edge and thats that. using clay along the spine area does much the same, and is a bit easier to accomplish with larger blades and less experience.
|