Aguilla Blanca said:
What modern gun makers call "color case" finish is not a true case hardening process, which they don't need because their frames are hardened all the way through. Rather, it is a chemical (I believe) process that is a finish, intended to replicate the appearance of the case hardened firearms of days gone by. They have to call it "color case" because they can't honestly call it "case hardened" -- because it isn't case hardened.
Not quite true. The older Ruger Vaqueros were chemically colored. However Doug Turnbull, and I believe many others, use a heat induced process. Case hardening is indeed done on some of the Italian clones, as well as the Colt Single Action.
True case hardening leaves a dull gray looking finish, look at a file for example. Using bone, leather, or even cyanide adds the mottled colors during the heat process.
Ruger Blackhawks are hardened through, but I believe Turnbull's treatment also adds some surface hardness.
And, the trigger and hammer on some of my revolvers are case hardened to provide extended wear on mating surfaces.
The hammer and trigger on this Ruger have been case hardened, and I asked for the hammer sides to be polished bright:
This was don around 1989, and the sear surfaces show no sign of wear after over 19,000 rounds being fired.