Howdy
True Case Hardening is done by placing the parts in a closed container packed with carbon bearing materials like leather and charred bone. The container is then placed in a furnace and heated. Sorry, I don't remember the specific temperature. The raised temperature causes carbon from the leather and bone to migrate into the surface of the steel. How much carbon migrates into the steel depends on how long the parts are heated. The container is then removed from the furnace and the parts are quenched in water.
Raising the carbon content at the surface of the part increases the surface hardness of the metal. True case hardening can be done with both iron and steel. The carbon does not migrate very far into the surface of the steel, only around a millimeter at the very most. Usually considerably less. So the surface, or Case, of the metal has been hardened, while the underlying metal retains whatever ductility it originally had. This combination of surface hardness and underlying ductility is ideal for parts like revolver frames, hammers and triggers that need the surface hardness for wear resistance but need to retain ductility so they will not shatter from impacts.
The colors of true Case Hardening are a by product of the process, nothing more. They do not impart any strength to the part. The colors can fade with exposure to harsh chemicals and even sunlight over time. In the past, the colors of true Case Hardening became a major selling point for gun manufacturers, so each maker jealously guarded their process. Modern refinishers like Doug Turnbull have recreated some of the old methods of producing brilliant colors, but the colors are still only a byproduct of the process. Turnbull can also create brilliant colors on Rugers, but he is not actually Case Hardening them.
Case Hardening was a good solution using the low and medium carbon steels of the 19th Century for hardening the surface of the metal. Ruger uses a modern steel for their frames and they heat treat the steel so it is hardened all the way through, not just on the surface as with Case Hardening. That is why Ruger was using a 'fake' process for putting colors on the Vaquero frames.
Case Hardening is one of many techniques for adding carbon to the surface of iron and steel. The general name for these processes is Carburizing. One very common application is for screws. Metal screws sold as Black Oxide have been treated to raise the carbon content at the surface. Another common way to surface treat steel to raise the surface hardness is a chemical called Kasenit.
There is a video floating around on U Tube that shows part of the process for assembling Uberti revolvers. One scene clearly shows the frames being dipped in a chemical bath of some sort and the narrator says this is the hardening process. Clearly not true Case Hardening.
I agree with CraigC, the Bounty Hunter colors do not appear to be true Case Hardening. Bottom line is, true Case Hardening is labor intensive which makes it expensive. If you want real Case Hardening, you are going to have to buy a Colt or a USFA and pay for it.
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I own Colts, Rugers, and Ubertis. If you want a transfer bar, buy a Ruger. They have been putting them in since the 1970s, everybody else is a Johnnie Come Lately.
Otherwise, buy an Uberti and learn how to load one, skip one, and load four more. It is not difficult.
