Gun Blueing

First and foremost...regardless of the condition of the gun, if it is a collector's item, DO NOT have it reblued...you will all but kill its value.

With that said, and assuming you intend to reblue for whatever reason, the best way is to have it done professionally. Hot blueing, rust blueing, charcoal blueing, nitre-blueing, case coloring, et al, require a fair amount of equipment and expensive chemicals to do the job right. Also, make sure the person you get to do the job is experienced...ask for references for his work. Just having the equipment alone does not guarantee good results. Good blueing is 99.9% preparation work. If the prep is bad, the whole job will be bad.

Forget the cold blueing. It's ok for touch ups of small areas (emphasis on "small"), but to try to do large areas, or even entire barrles/actions is an exercise in frustration. Even if you manage to get a good, deep color without lots of streaking, cold blue does not penetrate the metal very much and it will scratch off or even wipe off easily.

thank you four time jim parker

The most durable bluing you can get is rust bluing. The finish is literally rusted into the metal. This is also one of the most expensive bluing jobs as well. It takes time, usually a week or more. Rust bluing is usually done almost exclusively on barrels since this process allows you to plug the tube up in order to keep the bore shiny and smooth.

The next most durable would be charcoal bluing...it is also, in my opinion, the best looking as well. The finished color, especially on well polished metal is very similar to the results of nitre-bluing (also called "heat" bluing). The color ranges from a bright, almost peacock blue to a deep, almost purple. Very beautiful.

Nitre-bluing is a heat process as well and is done using mixtures of special salts that are first melted over heat and then the parts dipped into it. Nitre-bluing will produce a range of colors, depending on the temperature and length of time you expose the parts. The colors can range from a straw yellow (called "strawing"), to deep purple. Interestingly, the bright peacock blue (the most common color achieved with nitre-bluing) does not come until after the deep purple color.

Unfortunately, nitre-bluing is not done much these days. The problem is with the modern steels used in guns. Right after WWI, our steels changed in alloys, etc and nitre-bluing just doesn't work well with it. Charcoal bluing does a pretty good job of getting that bright blue color though and works well on modern steels.

Another common and popular bluing method is called "Hot" bluing (not to be confused with "heat" bluing, ala charcoal or nitre-bluing). Hot bluing is also called "salt bluing". The part is placed in a hot solution of salts until the color is achieved.

Lastly, and although not a "bluing", case coloring (or color case hardening) was very popular as well, but much less so today, except on custom work. A piece was wrapped up in all sorts of "special" materials, chemicals, etc and more or less put into a fire. The various, haphazardly placed materials interact with the metals to create swirls of color. Very pretty when done right and with the right alloy.