I use a cheap lacquer if the barrels need to be etched, it cleans out with solvent when finished.
I'm not convinced that immersing pairs of barrels in the etching solution is a good idea any more, too much risk of letting a corrosive chemical in between the barrels and ribs. Tend to carefully swab etchant on now if it's needed, which is not every time.
I leave bores untreated when blacking, just take care not to let any solution in , keep an eye on them during the process and give them a bloody good clean and oil when finished.
