Just got to thinking about my old bud Charlie Maggard. He made excellent repairs, and always seemed to get a beautiful butternut-brown finish on steel. I finally pinned him down as to the secret ingredients. He grinned, and opened a tall cabinet in the corner of his workshop. Inside the cabinet there was a gallon jug of distilled vinegar, and a wool blanket enclosing a barrel being browned. It was suspended over a pan of warm water (his workshop wasn't refrigerated, and summertime in Phoenix was a bit over 105 degrees in the evening). Warm barrel treated with vinegar, and enclosed over warm water. For him, it worked perfectly.
I guess it's not just the ingredients, but the details and know-how that ultimately determine results.