Does anyone have any suggestions for dealing with the milling of
white gold? I have melted together an old 14K white band(for
sentimental purposes) with 7dwt new casting grain(H&S Palladium
white) into a bar with the intention of milling it into square wire
and making a new band with a prong setting. I am letting the ingot
air cool, then when starting to roll it, I am experiencing extreme
brittleness and immediate cracking. I am rolling all in the same
diection, taking very small reductions at each pass, and annealing
often, but still experiencing the problems. Have never experienced
this problem with other colors of gold before, but this is the first
time I have worked in white. Any ideas?
Ron: the last time I saw gold cracking with the first pass on the
rolling mill I found it had been contaminated with lead. Sounds like
you have some contamination there somewhere. I suggest you start with
a fresh lot of pure and try United Precious Metals #930 white alloy
for 14kt. I use it for both casting and milling and have never had a
problem with it being brittle or too hard. I even use it for pave and
bead and bright cut. 1-800-999-fine . (usual disclaimer goes here)
Talk to Dave Zimmer he has been very helpful with my questions. Frank
Goss
Karen, your problem is mixing palladium white gold with ordinary white
gold. Nickle white gold has very different working properties
because it is not a true alloy in the sense that yellow gold mixtures
are. In the case of complete nickle gold metals, you should not
quench it at red hot temps. In fact it is better to quench it when it
has lost its redness in alcohol. The alcohol will not quench the
metal as quickly therefore keeping the grain size of the metal in a
more workable state. The problem is that palladium alloys work much
more like yellow gold in annealing. You may be forced to refine the
lot in question and start from scratch. Sorry,
Sorry Ron, the problem is that you mixed nickel white gold with
palladium white gold in your melt. You’ll have to send it to the
refiner - those two alloys do not mix together well at all. Start
over with just the palladium alloy, and adjust your price accordingly.
Palladium is over 800 an ounce right now. Ouch.
Hello Karen! You have brought back an old nightmare! Been there, done
that. No recourse, get new white gold (palladium white is nice, if
your budget allows) and start your project. Send your mixed metal in
with refinings. No hope in using it, sorry. I would guess it is a
very simple rule for a metalurgist. My thought is the nickel and
palladium are incompatible for some reason of atoms and molecules. I
am sure someone has the details. Now what have I started?
Good luck! Tim
Karen, The old band that you melted was probably nickel white gold.
Mixing paladium white and nickel white golds is a recipe for disaster.
Those I know who have tried it describe the same problem that you are
having. Nickel white is bad enough when it is fresh, consistent alloy,
but when you mix alloys, even nickel whites, things change. If you
start over, I’ve found that when annealing, if you allow the metal to
lose it’s red glow and then quench it in denatured alcohol, the
cracking is much biminished. Something to do w/ the rate of cooling, I
think.
Re your problem with white gold. Sounds to me that you are doing all
the right things: ari cooling, annealing, slow passes, etc. so there
shouldn’t be any problems.
What comes to my mind is that you are working with an unknown alloy in
the original band which is probably a commercial casting alloy that
contains nickel. It is the nickel that makes white gold behave badly,
the brittleness and stiffness etc. Then you combine that with the
palladium white from H&S which theoretically should improve
malleability and other working characteristics. Theoretically. But
what may be happening is that the two alloys are interacting in a
strange way due to something that a only metallurgist would know
about.
You can call Tory at Hoover and ask him what he thinks. He may
transfer you to the metals expert there. Those people are very
helpful in that regard, so don’t be bashful.
Even when you know the cause, you are still going to be stuck with the
problem, I would guess. I would talk to the client and explain the
dilemma and then try to persuade the client to use new metal. I
usually decline to use materials provided by the client for just this
reason. If they insist, I would agree only on condition that they
accept the risks from the unknowns.
Let us know how you came out.
Riccardo Accurso
Ricco Gallery of Contemporary Art Jewelry
125 W German St /PO Box 883
Shepherdstown, WV 25443-0883
Dear gold smelter. I am sorry for my late reply on your problem But I
just saw it. The thing what is happening in the white gold, containing
palladium and nickel, is an intercristaline hardening process. This can
happen when the metal is changing from liquid into solid state… When
the metal is cooling down from the liquid phase into the solid phase,
the alloys are pushed to the crystal edges.The nickel and palladium
are well fitting into each other and are walking together to the
crystal edges. Here they form wedges between the crystals. The metal
is not ductile anymore and has a high strength. To prevent this
walking a fast cooling from the liquid to the solid state is
necessary. This also happens after you heated up the metal above the
recristalisation temperature (for gold approx. 650 degrees C) and let
it cool down slowly the alloys then have time to move. But in
metallurgic we now also an other process happening at low
temperatures, this is called precipitation hardening. The alloy(s)
are creeping over time to the crystal edges. This is a process of time
and can be speeded up on a higher temperature.(remember the hardening
of 14 K gold alloys at 250 degrees Celsius). In the industry aluminum is
often treated this way. High strength means that you can use less
material and build lighter constructions. Aluminum rivets in airplanes
for example are alloyed with copper. They are heated up above
recristalistion temperature and sqeeched*. The rivets are now soft.
But after 6-10 hours the hardening will occur. If you want to rivet
them after this time they will crack.
Now you will say what does this means for my gold. I don’t know, it
is one of the three things, ore a combination mentioned above. You have
to try to get the alloys back into the crystal of the gold again that
for shore. Casting a sheet you can do in a metal form (fast cooling)
or in sand like the Delft casting method (slow cooling). If neither
effects the structure of the metal you have a problem with the second
two points. I have had also some alloys with give shit gold but the
way to get at least a sheet out of it is like this: Hammer after
casting it until to build up some internal tension. Not so hard that
cracks occur. The build up internal pressure by hammering, brakes down
the crystals at recristilisation temperature. Then glow it to dull to
cherry red (shortly) and let it cool it down in air below 400 degrees
C (until you see now glowing in a dark room) and then cool it down
fast in water. Not in acid, because acid eat up in the crystal edges
copper and zinc residues. This will give a starting crack which will
grow during rolling. If you heat it up for a long time the crystals
will grow again and the alloys will settle more to the edges. The
smaller the crystals, the more ductile the material will get, and the
less problem you will have with the wrong alloys.(because there is
more edge surface). Next start rolling it only a few % until you feel
it hardens again. Glow and sqeeche again. This can take a lot of
steps. It is better to do it once to often, than to go over the edge
and have cracks again. If you are lucky and get the thickness reduced
to approximately 35% you will see that it gets ductile again. You will
have now fine crystals. The material will never be as good as new
bought gold, but it will be workable. It also helps before work on
this material after so time, to glow it first to get it softer again.
If everything will not work the only thing to do is cast some jewelry
out of it. This is my way to get rid of shit gold. Good luck and if you
have some questions don’t hesitate to ask.