| I'd be very careful going down the caustic route on a DIY route. IMO, have a word with whoever is going to reanodise it for you and have them do it.
The anodising on the arm is more cosmetic than an engineering finish and won't be very thick. It'll probably polish off. It'll need polishing before refinishing so you'll be half way there.....
Alloy can dissolve at an alarming rate unless you're careful and know exactly what strength you need and/or are dealing with. | 
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