One thing that I have always loved about firearms was the classic looks of color case hardening. Too many people fail to understand what this is, how it is accomplished, and why it is done other than just looking cool. Sadly, most people these days see it as “cowboy stuff” and don’t give it a second look. Definition from Wikipedia:
Case hardening or surface hardening is the process of hardening the surface of a metal object while allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal (called the “case”) at the surface. For steel or iron with low carboncontent, which has poor to no hardenability of its own, the case hardening process involves infusing additional carbon into the case. Case hardening is usually done after the part has been formed into its final shape, but can also be done to increase the hardening element content of bars to be used in a pattern welding or similar process. The term face hardening is also used to describe this technique, when discussing modern armour.
Because hardened metal is usually brittler than softer metal, through-hardening (that is, hardening the metal uniformly throughout the piece) is not always a suitable choice for applications where the metal part is subject to certain kinds of stress. In such applications, case hardening can provide a part that will not fracture (because of the soft core that can absorb stresses without cracking) but also provides adequate wear resistance on the surface.
As it relates to firearms, this process was originally intended solely as a protective layer from the elements. Think of it as an old school Duracoat job, only prettier.
Here is Larry Potterfield giving a brief demo:
Unfortunately, this process is rather involved and time is money. Rossi has utilized a rather ugly way of chemically “case hardening” some of their lever action offerings. This process is hideous and is not as durable as the original process. The case hardening on my H&R Topper is why I haven’t given it a more modern paint job. I can’t in good conscience, ruin that beauty.