I’m not understanding how the process with LMF can go bad unless it was left way too long to rust or if it wasn’t rusted and carded enough? The stuff is great and I’ve had no issues with it browning or rust blueing.
I make exactly two deviations from the instructions if rust blueing and exactly one deviation if browning. If blueing I will apply one coat only and when it rusts I will boil and card, I do not apply a second coat and I do not wait 3 hours, I wait for the rust to tell me when it’s ready and not the clock. The second coat, for me in a moderate to high humidity area, will pit the metal it is applied before boiling and carding, and if 6 hours from first application to first carding it will pit bad enough to warrant draw filing and sanding back bright. Bear in mind I only have done ‘as new’ finishes. For browning I apply one coat and one coat only, then card when ready. Two or three passes will make a great brown, neutralize and oil it’s done. For blueing I’ve gone as far as 10 coats to get a dark but smooth finish.
I have used a sweat box and it definitely speeds up the process, just make sure it isn’t humid enough to wet or condensate on the part or it will pit. It doesn’t take a lot of humidity to work. I’d guess that 40 or 50% is perfect if you want to do one coat per day, 70-80% brings that time down to a couple hours between carding and the next application.