if pickling with alum really works so well, why did nobody
ever tell me about it??? I've always been taught to pickle with
sulphuric acic, but I really hate it. Also in literature I did
find no hint on alum. So maybe there are any good reasons to
keep working with acid instead of alum?
Sure. Acid is faster. And a bit more effective. Alum will not
quite get the fire scale as effectively, especially on some gold
alloys. But then: what’s this about not believing it just cause
you can’t find it in print? Who’ever said the books are
complete? Hah! Most of em are the basics. Pickle is used cause
it’s long lasting and effective. (I assume you realize that
almost nobody actually uses sulphuric acid itself anymore as a
pickle for normal jewelry work. We all use Sodium bisulphite,
sold as sparex or other such. It’s a sulphuric acid salt, and is
much safer to use, while being almost as effective.)
Alum is gentler and safer yet, but not as effective. If it
works for you, great. But few professionals are in any hurry to
switch. On the other hand, many of those same professionals ALSO
have a beaker of alum solution sitting around for when we break a
drill bit off in the work. Ordinary pickle will dissolve the
bit, of course, but then makes a mess of other work as a result,
and especially the piece with the broken bit gets heavily copper
plated while the bit dissolves. With alum, you don’t get this
copper plating, and if you boil the solution, the broken bit is
And what about stones? If you've done a repair on a piece
of jewelry with the stones in place, is it possible to pickle
the piece in alum without damaging the stones?
Alum is no more dangerous to the stones than is pickle. Any
stone which should not go in normal pickle should not go in the
alum either. Alum works for the same reason sparex pickle works.
It’s an acid salt. Some stones which should not go in pickle
are things like pearls, turqoise, malachite, amber, coral, jet,
lapis lazuli, peridot, and “soude’” type doublets (many of the
green spinel synthetics. The acid sometimes attacks the glue
bond between top and bottom pieces…) I wouldn’t put any of
these in alum either.
Hope this helps.