Everyone seems to use something different. I have been using Pilkington's Classic American Rust Blue for at least 10 years. If you leave off the last step, boiling, it leaves a beautiful, authentic brown. Brownell's sells it. I have to clean the metal well, with denatured alcohol, handle it with rubber gloves, and it works much better with warm temperatures and fairly high humidity. I think the latter helps with any of the cold rust browns and blues. However, in low humidity conditions, with a good polish job, one can achieve an almost translucent high gloss brown or blue, but it takes lots of patience. I consider LMF to be a little more touchy in application that Pilkington's. I just don't like Plumb Brown. I am a hobby builder, and there are many professionals in this forum. Consider the source when weighing advice.
Frog