problem with a typical brush ferruel, there not stainless, start mixing material current and a acid and you can leave all sorts of residue. Now if its something pure like titanium, you might be fine, but a typical brush ferrule which is chrome plated steel, you could end up really screwing up a part.
Polarity, i never remember, but just try one, the correct way around is pretty obvious results wise in seconds, incorrect way with fresh acid, clean brush does nothing much noticeable!
Voltage - current is all down to acid strength in all plating applications, all affected by current densities too, yes to a degree higher voltages work faster as does stronger chemicals but it can leave a rougher finish, get the voltage right and you can get a electro polishing effect, but its kinda fiddly. I have used both the tig as a power source in stick mode turned down to 10 amps (0 arc force if your set has that option) and it worked fine, equally i have also done it with a small circa 12V regulated power supply, Not a battery charger. IMHO you don't want too much power, the brush wears and especially if your using the rag covered wand approach it seams to realy eat through any material i have tried for the cover, metal to metal and you get a arc, which leaves a nasty mark! Less power smaller mark!
