The solution composition makes a difference according to what I have read. The experts also say the the heat-treatment condition of the metal makes a difference. I agree with that. In my experience, the modern alloy steels like 4140 are difficult to rust blue. The straight carbon steels in old guns usually rust blue nicely unless they have been previously case hardened. If you don't get a good blue in 6 rusting cycles, you are wasting your time
I doubt the solutions go bad with age since they are usually nothing but dilute acid and water. I have always used the Laurel Mtn. solution since it contains a detergent, making it much easier to use. There is no need to have perfectly clean metal when applying the solution or when carding. What I mean is, fingerprints are no problem. This allows bare-handing the parts with no worries about spotting the finish.
RAN
