While I am an long time Orchidian I have been taking a break from
everyday reading, but find myself often looking through the archives
for answers to my questions. What a wonderful resource we have here,
so thanks Hanuman!
My question is in regards to some 14 KPD rolling grain I purchased
from Stuller recently. I melted it into what I believe is a new
silica crucible seasoned with a light coating of boric acid. The
first casting was not to my liking so I remelted it in the same way.
I rolled it being careful not to reduce more than 50% then annealed
it, to orange heat, probably too hot, allowed the metal to cool on a
steel plate. Of course the next few rolls cracked it, but only
superficially. I was able to grind those fine cracks away.
Re-annealed to cherry, quenched in alcohol (after reading what Peter
Rowe suggested) rolled several more times then a big crack! The
metal has cracked on only one side, the other looking perfectly
fine. Anyone know what’s going on here? Contamination? My fuel is
oxy-propane, annealed with a slightly reducing flame.
Can I remelt the metal and try again, or do I need to add fresh
metal to the mix? Stuller thought there might be iron contamination
of the metal, but I have no idea how that might have happened. My
pickle pot has a ceramic liner, could there be iron oxides leaching
from that? Stuller suggested using a graphite crucible and quenching
in water after red color is gone from the metal. All the graphite
crucibles I can find are not sized for the small studio.
You can remelt it again it will be Ok just DO NOT use graphite,
alcohol is great for annealing (after initial 50% reduction) just let
the color disappear from the metal before quenching (as soon as it
goes grey) be gentle at the mill go little by little so it hardens
evenly.
What else is in youre alloy besides Pd and Au ? and in what
proportions?
I cant speek to what to do different with the 14k palladium but I
bet you could cut your own crucible from a graphite block. Looks to
be cheep and readily available online.
I spent some time today carving a small charcoal crucible and was so
glad that I had.
Susan-Did you forge your ingot before rolling? If not remelt. Forge
on all sides. Anneal. Then roll. Also do not cross roll with out
annealing before changing directions.
Borax is what is used.
Do not use a graphite crucible.
Once the metal is molten and rolls around freely, a small pinch of
borax is used if the metal needs to be cleaned.
When the metal is molten, pull back the torch until the surface is
free of anything floating on the surface, a mirror like surface
means it is ready to pour, if you hold the flame to close, it will
look contaminated. If you coat the crucible, very little borax is
used. Too much andit will flow with the metal into the ingot mold. A
little in the center of the crucible and as you heat it, move the
flame up the sides of the crucible, the flux will follow the heat.
Hold the flame at the front of the crucible keeping the metal molten
and pour through the flame.
I missed your original post but it sounds like youre having trouble
with white gold cracking.
I have just changed the way that I melt gold after getting some
from a refiner.
The short version is metals with palladium alloys are susceptible to
oxygen whilst melting. When I melt metals with palladium now I never
take the flame away from the metal. If the flame is removed whilst
the metal is molten oxygen from the air will enter the alloy. The
flame that you are using needs to be a neutral flame e. g. not too
much oxygen or too much fuel. I have had to switch to a multi-headed
torch instead of the single tip I used to use. The neutral flame does
not have as much heat as an oxidising flame therefore the multi-tip
was necessary to get the heat required to melt the metal. I keep the
flame on the metal as I pour it into the mould as well.
Another helpful thing Ive found recently is a way of preventing what
I call pin-holing in the surface of the pour. The pin-holing is a
result of the metals being poured at too high a temperature. As the
metal calls from the higher temperature it contracts and causes holes
to form in the top of the pour.
As a result of using this method I can take metal straight from the
pour to the rollers with excellent results. I can take a bar straight
from the mould and place it in the ring benders and form it into a
ring even at thicknesses of 6 mm without surface cracks.
I use oxygen propane gas and silica ceramic crucibles.
This has been such a great help to me after working in the trade for
nearly 40 years. In the past I would melt white gold and sometimes
the same piece of metal would work well one poor but not the next. I
couldnt work out why. But this new method has solved the problem. It
sounds simple but it works. I hope you find it useful.
Thanks everyone for your useful suggestions! The third remelt went
fine and there were no cracks after rolling. The tender touch was
the answer here!
The day after I posted my question, a gentleman by the name of Paul
Welch from Stuller called me and we spent a good amount of time
talking about my process but he was unable to determine a specific
culprit.
I told him about the crucible being seasoned with boric acid, and he
said that was okay. He didn’t flinch when I told him I had probably
overheated it. Quenching in water was fine. When I asked about
remelting he told me that Stuller uses very small amounts of zinc in
their 18KPd rolling alloy, and with heating it vaporizes out of the
melt. Makes for tough remelting once the zinc is gone. I still have
to wonder if adding a little fresh metal to remelting clean scrap
would make it reusable.
While this little project is challenging, I sure have learned a lot,
took notes which include all of your suggestions.
You can also try to add pinches of Boric acid before you pour the
metal and small amounst of borax before you melt. This should
prevent oxidative porosity.
I was really surprised to learn that Stuller uses very small
amounts of zinc in their 18K Pd rolling alloy! I wonder why they
would do that. I make my own Pd white gold and just use pd, silver,
and copper. It rolls out fine and is very pleasant to work with.
I think a major cause of faulty ingots is using a metal mold
which is not hot enough. If you are alloying small amounts, I have
found it much better to carve out an ingot shape in a charcoal block
(get the longer-life kind) and pour straight into it! No problem
with heating the mold, no problem with sticking, and it gives you a
reducing atmosphere. I find that using a mini torch with a melting
tip on oxy-acetylene causes no damage at all to the charcoal block
ingot mold after many pourings…
1. I was really surprised to learn that Stuller uses very small
amounts of zinc in their 18K Pd rolling alloy! I wonder why they
would do that. I make my own Pd white gold and just use pd,
silver, and copper. It rolls out fine and is very pleasant to work
with.
I make my own 14k Pd white and the zinc helps with several aspects
of making a good rolling alloy even though it is more important in
casting alloys. Here is an excellent paper on alloying elements for
gold alloys and what they do good and bad in the alloy.
Optimizing Gold Alloys For The Manufacturing Process
I can recall during a casting course in Germany (Harbach) that the
teacher always added a small amount of pure zinc in a crucible (500gr
molten metal) .
It improved the fluidity quite a bit according to this older
knowledgable person.
Another advantage was that it toke care about excessive amount of
oxygen in the fluid metal.
It only toke a 1cm " of zinc being about 1mm thickness to get the
job done and a good stire with a carbon rod.
The piece of zinc immediately disappeared as it hitted the molten
metal.
I still don’t understand why the zinc doesn’t evaporate a soon as it
is untroduced to the molten metal but appearently it does the job.
I never encountered problems anymore with my castings following this
procedure.
Here is an excellent paper on alloying elements for gold alloys and
what they do good and bad in the alloy. Optimizing Gold Alloys For
The Manufacturing Process http://www.ganoksin.com/gnkurl/12k
Thanks James. Interesting article. My concern is always the melting
point, as I usually use several alloys in the same piece.
Re Jo H.'s advice to forge on all sides then anneal prior to
rolling. Doesn’t the annealing ‘undo’ the molecular alinement you
achieve from forging? What does forging on all side accomplish?
Isthis advise also applicable to high carat gold? I’m never really
sure if I’m getting a benefit from forging before annealing. Thanks
to those who know these things for sharing their knowledge.
I had the same problem with my 18 carat palladium white gold. The
refiner told me palladium white gold is a very sensitive to oxygen
from the air or from an oxidising flame. It?s a palladium in the
metal that does it. You need to use a neutral flame and keep this
flame on the metal at all times so that the molten metal is not
exposed to the oxygen in the air. When you pour the metal play the
flame over the bar in the skillet to prevent the oxygen from coming
into contact with the metal.
I have done this for about a year now and my palladium white golds
roll like they have just come from the refiner’s. I have passed this
technique onto other jewellers I know and they have had the same
results.
This will only work if your metals are clean. Unfortunately if you
have impurities in your metals this technique won’t help.