Most of the older gunsmithing books have recipes for blueing and browning, if it will brown, it will blue, but some formulas are better than others. You also have to remember that alloys of steel are different today than they were in the past and some of the old recipes may not work as well, or at all with todays' steels. Thrre is also the toxic factor, many of these formulas involve chemicals that are not good to work with, and are somewhat expensive. You can brown with plain vinegar, salt, or even perspiration, though the results probably won't be as good as some others, it may be a more historically correct method than a lot of others. I personally won't mess with making these solutions anymore, except for aqua fortis, which is difficult to get anymore for stock stain, I tend to buy a product called Barrel Brown and Degreaser, this is excellent stuff, only mildly toxic, and really does cut through grease, if you still take the time to carefully degrease the metal and use a damp box you will obtain rich lustrous browns and blues that will be the envy of all who see them. Another point to consider is this, we tend to spend a lot of time these days blueing and browning metal parts on our creations, though in the past this probably wasn't done as much as you would think, I believe after research and talking to many knowledgeable people, most colonial arms were left in the white, or charcoal blued, and have over time developed the patina that we admire so much and believe to be brown purposely put there by the gunsmith.
