What is the solution to removing the reddish firescale from nickle
based white golds? I've tried nitric with no success.
Peroxide/cyanide bombing will do it, but sometimes needs several
tries. But I'm going to assume you're likely not equipped to do that
Sulphuric acid pickles generally work better than nitric based ones
too, in my experience. Using the actual acid works somewhat better
than the acid salt pickles like sparex.
You might try the old trick used to remove copper flash from brass
or pieces pickled in contact with iron, that being mixing some
hydrogen peroxide with good fresh sodium bisulphate or sulphuric acid
pickle. I don't know if this would work, but suspect it just might.
Cheap enough to try, at any rate.
But the bottom line is that fire scale on nickle white golds is
nasty, and often just abrasives are easiest. And the real solution
is to avoid it in the first place. Be sure the metal is clean before
soldering or heating. Be sure you've got an ample coating of boric
acid/alcohol fire coat. And finally, do NOT use the white paste flux
types. For reasons I'll never understand, although these fluxes
promote solder flow wonderfully, both on white gold and silver (and
other metals), they also seem to almost promote the formation of
that fire scale, perhaps because they seem to burn away and become
depleted/used up a moment or two before you're quite done soldering.
If you stick with the less active, but more long lasting, Batterns
type flux, or similar "self pickling" formula, you may find that you
simply don't get that fire stain very often.