Note that in either case the Colors are superficial, being only at the surface. The Case is the depth to which carbon has penertrated & alloyed with the steel, allowing it to harden at the quench. Carbon penertration is a combination of temp & time. I am not certain what the absolute maximum is for either method, but as normally done the charcoal method results in a deeper case than the normal Cyanide method. The loss of color is purely cosmetic & in no way affects the integrity of the steel beneath.
