I am a Pharmacist , and have a fair amount of Chemistry experience also. (Not as much as Mr. Apperson tho). I do not see any need to do the dipping method vs the brushing on. I have done quite a few barrels using FeCL4 as an etch to bring out contrast and I use a medium stiff brush and about a 7-8% soln which works great. About 30 seconds to a minute of wetness and then fine wet steel to scrub off the excess stuff.