I have lots of experience with the Casey Cold Blue product, and several other cold bluing products. Almost 50 years of experience using it.
The reason that guns are "blued" to begin with is so that the bare metal does not rust. Bluing is a complicated process, involving very hot temperature chemical baths, which end up putting a finish on the metal that will resist rust (but not totally prevent it.)
Cold Bluing is just a chemical in a bottle, that you wipe on metal, and then wipe off, which gives it a blue look, (or in case of some of the products such as 44-40 cold blue, an almost black look.) It provides no protection against rust whatsoever. It is just a coloring. And, it is not permanent. It can and will wear off with handling and use. It is primarily used for touching up small areas on a firearm where the original bluing has worn off, and you don't want to spend $300 for a hot blue job. It is also used when you find a cheap, inexpensive gun, that has old worn out bluing, that you want to make look better, particularly when the gun is not worth $300 to being with. Finally, it is used to "blue" very small replacement parts, such as a thin trigger guard, etc., that are not worth sending off to a gunsmith to get hot blued.
In order to apply it, and have it look good, the metal must be absolutely free of rust, and absolutely 1000% cleaned first of any grease or oil, including your fingerprints. All of the companies sell a "degreasing" liquid that you must apply first, and wipe of with a clean cloth. Often, people just use acetone, or 98% isopropanol.
The problem with the cheap cold bluing process is that it is real art to apply it and make it look uniform in color. After you clean it, you must heat up the piece of metal, to about 150 degrees or so with a heat gun, and then wipe the product on with one even stroke with a soft clean cloth, and then immediately wipe it off with one even stroke. If you don't do all of this, then the metal will be blued, but it will look splotchy, with dark and light areas. (By the way, it is poisonous.)
Often, you have to do this three or four times to get it to look deep blue. (The 44-40 goes black really quickly though.)
Once you have achieved the desired color, you have to quench the metal with a light oil, such as gun oil, and let it cure for 1 to 2 days. If you have done absolutely everything right, you will have a nice uniform blue color, or blue black color, that will last for a fairly long time, if you don't unduly handle it. And, guess what, it is not a shiny finish. It is dull, and you must keep a very light coat of oil on it to make it look light real hot bluing and keep it from rusting
Now, having said all of this, I can't imagine why anyone would use this product on his model train track. Really.
You can be sure that the rollers on your engines and cars will wear it off.
Birchwood Casey also makes a black "touch up" pen, which is used on black aluminum gun parts, when the black adonization wears off. I have used this as well. If the aluminum is absolutely clean, it will go on fairly thick, and dry really fast. It will dry to a glossy black. It just a paint, but is pretty darned tough. I can't imagine how many of these paint pens it would take to do a large track.
Hope this info helps.
Mannyrock
