Surface hardening

[JCKelly]

I think Kasenit was potassium ferrocyanide with some charcoal or soot added.

Nicholson File used to use a "cyanide loaf" to coat their files for heat treating in a lead bath. This was potassium ferrocyanide, table salt, and flour.

Courtesy Our Gov't they had to stop using the ferrocyanide, so much for best quality American files. Long time ago, anyway.

Personally I do not use table salt containing ferrocyanide.

[bob in the woods]

JC Kelly- I believe that many of the India made flintlocks have their frizzens case hardened using the method you just described.