There is a good six page article in the August, 2002 issue (Vol XVII, No 8) of the American Gunsmith, "The Official Publication of The American Gunsmithing Association," on nitre blueing. Among other things debated here that are discussed, they mention Brownell's as the source of obtaining the proper equipment AND CHEMICALS. They state the Brownell's salts are a mixture of potassium nitrate, sodium nitrate, and sodium nitrite, continuing with "Brownell's salts aren't quite the same as the original formula (not at all uncommon for a modern chemical formulation) but they do a very good job of duplicating the proper straw and blue colors."
That's certainly my experience, and they have continued to sell this product for many years. It matters not to me (or to the piece of steel I am coloring) that the formulation of the chemical is modern and not "original," the end results are what matters.
I can make a copy of the article available for anyone that really cares about reading it.
