This process is also called chemical stripping. The
solution can only be used once and must be disposed of at once.
It will foam up in an ugly brown stuff after about 3 minutes.
Don't let it surprise you.There is no metal loss and the process
is especially good for discolored gold such as soldered mesh
watch bands and delicate castings.
And what, pray tell, Tom Arnold, is this ugly brown stuff that
is foaming up? Better safe than dead! Rose McArthur
Aw heck. can’t let it go a second time.
There IS metal loss. Just not much. Like electrostripping, at
least a little of the gold is removed from the surface. THAT is
what the brown color is from, for heavens sake. Hot solutions of
cyanide, especially with peroxide in there as well, are dissolving
metal at a fairly significant rate…
Now, on a normal cast or fabricated piece of jewelry, you’ll bomb
off less than you migh polish, and if you get the process working
right, you’ll get a nice workable finish will less metal loss than
by actual polishing. But occasionally, for example, one has to
bomb a piece several times to get it right. If that happens to be
a repaired thin hollow rope chain, where the metal is very very
thin you may find yourself having bombed too much off the piece…
In my view, though, the above is only an example why hollow rope
chains are trash, and not a reason not to bomb. And, for that
specific type of item, I frankly know of no other method that is as
effective at taking a worn looking piece of jewelry and restoring
it to a really sparklingly clean and bright like new look. You can
polish the outside of a chain, but not inside all those little
crevices where bombing is just as effective. Even electrostripping
on such items doesn’t come close. Magnetic tumblers, with their
tiny pins, are the next best bet, but not as bright a finish…
Now then. How I do it…
First off, I prefer to bomb with Potassium cyanide instead of the
sodium. Seems to have more of a kick to it, and goes brighter.
You can get cans of granular KCN from Vigor.
I use boiling water. Usually about a half cup, with only a small
batch of jewelry at a time. I do this in a half gallon plastic
pitcher, with an old gallon plastic gallon milk container who’s
bottom and half of the front has been removed as a spash sheild.
(more on that in a moment.) A generous teaspoon or so of the
cyanide powder is dissoved in the boiling water, either before or
after the jewelry is added. The Peroxide I use is 30%, stronger
than usually sold for hairdressers use. nasty stuff. will burn
your skin. For the above amount of water and KCN, I add about 2
table spoons or so of peroxide. maybe a little more.
IMMEDIATELY, the milk jug/splash shield is placed over the pitcher,
AND HELD DOWN. The key here is that it’s a very loose lid, doesn’t
seal anything. Just diverts any splash back down into the plastic
laundry tub I use underneath. This is, of course, all done with
good exhause ventiallation.
while many people who bomb use lower temps and concentrations, I
WANT my solution to explode. The better the “POP”, the better the
finish. Without that pop, the gold will be real clean, but it
won’t have become bright polished as well. Done 2 or three times,
this can bring a piece of gold sheet from the finish left by a
plain rolling mill to a bright surface that’s only slightly
imporoved by rouge, and doesn’t really need it. Since many of my
pieces are intricate constructions almost impossible to
conventionally polish, I find bombing to be invaluable. it will
not only leave a nice final finish on all the recessed areas, but
it will remove any soldering discoloration or fire scale from the
gold as well. Note that different alloys respond differently.
Standard 14K yellow golds seem to work the best. higher copper
content makes it less polished, and sometimes spotty. More silver
content makes it brighter. Apparently, the zinc in many 14K golds
also helps. Many 18K golds don’t respond as well, sometimes
comeing out not bright, but showing instead an etched crystaline
finish, which would me nice if it were more intense. White golds
tend to go matte, not bright. So all in all, I find this most
useful for 14K yellow work.
Also, a note on the chemistry. I’m not a chemist, but I’m told by
several folks who are, that what’s left, that brown residue, is not
cyanide anymore, but cyanate. The peroxide oxidizes the cyanide to
cyanate. Cyantes are still not benign compounds, mind you, but
they are a good deal less toxic than the original cyanide. So long
as you’ve used sufficient peroxide for the reaction to complete,
the wastes are not as toxic as you may have thought. Still, handle
the stuff with the respect due to such materials. The waste may
contain sufficient gold to warrant saving it. I put it into a wide
mouth container on a low temp hot plate that will evaporate the
stuff, producing either a concentrated sludge or dry mass
(depending on how often I add to that flask) When sufficient
material has been saved up, it can be refined for the gold. Not
much, but enough to be worth the bother even so.
Hope this helps.