I use common Alum that can be purchased at a drug store in
powderd form, mixed with water in a saturate solution at just
below boiling temperature.
I whole heartedly agree with Ray. One more great use of alum is
if you break a drill inside the jewelry, you can boil the piece
in an alum solution and the drill rod will eventually dissolve.
It does seem necessary to boil the water, perhaps Ray can explain
Although not recomeded by many people if the plating cannot
be removed by polishing use a stripping procedure , either
electro stripping or my old favorite cyanide bombing.
In reference to bombing, I think it best if the process is
learned first hand from someone proficient with it. I prefer to
bomb next to an exhaust fan or under a hood. Many people panic
around cyanide, but jewelers have been using it for many years
without problems… at least without obvious problems… the
danger of course occurs when acid is mixed into the cyanide
creating a lethal gas. Bombing creates a controlled expansive
foaming that chemically scrubs surfaces, actually removing the
non-gold elements, and leaving an extremely thin 24k finish, a
bit like depletion gilding. I prefer using bombing as a
pre-plating step or as a method of removing oxides. It creates an
extremely even surface color, but not a durable surface color.