Chukarman, Not a smith or a rocket scientist but I agree with you that case-hardening is tougher than case coloring. The colors from case- hardening are the result of the process. In order to case-harden you are using low carbon steel and you have to increase the carbon content of the surface of the steel so that a thin outer "case" can be hardened by heating the steel to the hardening temperature and then quenching it. So the process involves two seperate operations.
Cyanide, Carburizing, Carbo-Nitriding and Nitriding are all processes of case-hardening, but Cyanide is the most common. The steels are brought to about 1500 deg.F and then immersed in a bath of sodium cyanide. The hardening then is only a few thousands of a inch deep, .002-.004. and the depth is controlled by how long it is left at the 1500 deg.f before quenching.
I believe the case-coloring is of the Carburizing process where the parts are packed in a metal container with a carbonaceous compound (bone meal) surrounding the steel objects, the heat is higher 1700 deg.F for a length of time depending on the extent of the carburizing action desired. Now the steel can be hardened and quenched like regular high-carbon steel, now if they leave this step out you would get case-coloring. IMOP. Dave
