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White gold cracking


#1

To quench or not to quench that is the question.

I’ve been using a white gold alloy mix (909) to make 14k that I pour
into ingot molds and roll out into bar stock. I then hammer out
basic bands of 4-7mm.

Though I’ve often had cracking problems this latest batch is really
driving me crazy.

My procedure is to melt the 24k in a crucible, add the alloy, clean
with boric acid/sal ammoniac/ charcoal flux, then pour into either a
warmed open face ingot mold or a sliding ingot mold. I anneal once,
lightly forge the ingot on an anvil. I then flux the surface with
handi-flux to keep the oxides down then heat on a charcoal block to
orange, let the color fade then quench.

On my first pass through the rolling mill, and it was a light pass,
I had cracking. I have both fused the cracks back together and
sometimes sawed and soldered them.

I contacted my supplier of the alloy and they advised no quenching
just air cool and anneal after reduction after about 10% which of
course takes forever.

One thing I observed was that when I get down to about 2mm square
the cracking problem disappears.

I thought I would bring this to the forum for advice and guidance. I
have a photo of a broken end grain where I snapped the bar to check
the grain structure.

I’m grateful for any input that would make this an easier process.
Sure I’ve thought of casting but don’t want to go that route.

thanks,
J.Richardson


#2

Try using borax only on the melt as flux - no boric acid. Stir well
with a quartz rod to make sure all the alloy/fg is melted all the way

  • make sure your flame is not too hot then pour the ingot. In an old
    crucible light some paper or cotton with light oil on it to create
    soot and coat your mold with the soot before you preheat it prior to
    the pour.

Art

Arthur Gordon, Registered Jeweler
Member American Gem Society
JewelSmiths
www.JewelSmiths.net


#3
Though I've often had cracking problems this latest batch is
really driving me crazy. 

Jim - Ah, white gold. Isn’t it just the pits. As one refiner told me
once, “Maybe it’s tired.” Meaning that it is beyond help at the
bench. His advise was to stir it with a green stick - like fresh off
a tree, which might help (It’s the gases generated by the resinous
wood). I’ve had good results by melting it into a ball with a
reducing flame, pickle it, and grind or file off the top surface of
scum. Also using brazing flux can help - it’s way more intense than
jeweler’s flux - at least mine are. Casting it, especially with some
fresh metal, can also rejuvinate it - why I do not know, but it
does. But - do NOT solder cracks - then you have solder in your bar,
and it doesn’t really hold anyway, not under the rolling mill. If
you do anything, clean out the crack (sawblade…) and fuse it,
using heavy flux. Generally I find the best thing is to try to clean
it with a reducing flame (we’re talking yellow), stirring, flux,
pickle, grind off oxides, etc. and then repour it. 14kt white gold is
probably the trickiest metal we use regularly. The problem is that
once you get that cracking it can be real difficult to get the gold
back to normal. I’ve had pretty good results by heating with a
yellow flame, flame stirring it, and pull away gradually so that the
oxides come to the top and cool there, and then filing off the skin.
These are just some strategies, though. They don’t always work, and
once that cracking starts it can be a real PITA. Heating carefully
to begin with is a good start, but it sounds like you know what
you’re doing, overall. Plus it’s very easy to say, “Don’t do it to
begin with.”, isn’t it? Casting tired white gold does seem to go a
long way towards refreshing it, too. Make sure to clean the crud off
the bottom of the button, if you do that…

http://www.donivanandmaggiora.com


#4

Jim,

you didn’t say where your alloy came from but you might want to try
the 930 from United Precious Metals. I use it for casting and never
get brittle prongs. After I have used a button two or three times I
will retire it and make mill stock out of it. This stuff is so
ductile and malleable you will not believe it. Has a good white color
also. Every jeweler that I have loaned some alloy to try has switched
to it. It is also great for bead and bright cut. (usual disclaimer
goes here)

Frank Goss


#5

Hi

Most nickel white alloys need to cool before a wet quench. If in
doubt, air cool. Works for us with nickel white alloys in general,
check with your supplier for the specifics.

Daniel Ballard
Precious Metals West
National Sales Manager


#6

Jim, if I read your description correctly, why do you anneal the
ingot (straight from the mould) once before rolling it? I think doing
that will create more crystal growth in the ingot which will lead to
cracking problems.

Try melting at the lowest possible temperature that ensures thorough
mixing, and pour into a warm but not a hot mould.

Adding scraps of unknown white gold to your mix will cause
brittleness if the scraps contain different alloying metals to the
ones that you are using.

Lead, tin, or some contamination may have sneaked in and it only
needs the tiniest bit. As a last resort before sending the ingot to
the refiners, try ‘cutting’ it with pure oxygen to burn out any base
metals. I do this by melting the ingot using an oxy/acetylene cutting
torch; when molten I press the cutting button on the torch to inject
pure oxygen into the melt. It will boil and sputter if there is
contamination and then calm down when the contaminants are burned
out. Worth a try, you may be surprised!

Regards, Alastair