Wrap around cladding on yanagis...
Been curious for a while now. The yanagibas produced by many high end makers have a small flap of low carbon steel that goes over the spine of the knife and extends a small way down the back of the blade near the choil. I know these knives have to "rest" for a a few months and straightened for de-banana-ification purposes. I'm doubting this extra operation is for the sole purpose of showing the skill of the maker. I it there to keep things straight after the equalization process?
..this has totally been bugging me for some time...
Just a guess, but I think it's there so they can stamp their makers mark into soft iron instead of the hard steel.
They make these by forge welding a tile of high carbon steel to a softer piece that is used to make the tang. The tile is not the same width as the softer steel so it shows at the upper portion of the blade near the tang or handle.
Some makers show some skill by making this area a decorative transition between the two materials.
It is done partially to add strength to the tang because there is less tension between layers.
Thanks Devin, that totally makes more sense than it wrapping over the spine.