As you all probably know. .to achieve a good cutting edge and a nice hamon, Japanese bladesmiths applied a mixture of clay, coal dust,ashes and some other ingredients on the blade except for the edge to keep the spine of the blade from cooling too fast and thus keep it flexible while allowing the edge to harden to its full potential.
Recipes varied from smith to smith and were very closely kept secrets.
What I am interested in knowing is a good recipe for this mixture.
Has anyone tried this selective hardening successfully ?
I have read all there is online and seen a lot on youtube. . but the exact recipe is never shown.
Any info will me much appreciated. Thank you.:)