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Annealling 14K gold


#1

Hi

I’ve been given some 14ct gold scrap by a customer who wanted it
converted into some jewellery. I have tried working the meatl into a
usable form, rather than just a melted lump, by casting it into a rod
and then milling and forging into the right size,

I know it’s 14ct because I sent a sample to the UK assay office for
testing but unfortuenantely that’s all they told me - nothing else
about the alloy constiuents.

However, i’m tearing my hair out because the gold is incredibly hard
and cracks as soon as I try and work it. I have managed to get some
of it down into sheet, but I can see cracks in the sheet and I’m not
sure that it is really of high enough quality to use!

I have read the article on ganoksin about metal quality and working;

but how can I know whether this gold has picked up impurities and
are there any ways around the hardness problems, for example can I
try holding the metal at annealing temperatures for many minutes…
etc…

Any thoughts much appreciated.

many thanks
Chris


#2

sounds like there is a bit of iron or solder left in the mass. To
refine: remelt adding a pinch (large pinch) of activated charcoal
powdered, and a smaller pinch (1:2) of sal ammoniac to the molten
metal in the seasoned crucible dedicated to gold ( don’t use the same
crucible for all metals). after pouring into your heated and oiled
mould (soot has a tendency to muck things up too much, by adding the
charcoal and sal ammoniac as a flux you eliminate the need to soot
the mould(s)) - the preheating helps prevent thermal shock and asists
the crystalline structure of the metal in recompacting/reorganizing
correctly, you can the remelt and pour again, this time, when the
metal looks like a molten rolling mass, use a graphite stir rod to
remove any remaining impurities. let cool to gray after the pour and
quench in water, or methyl alcohol ( although a good jigger of
everclear never hurt!) or used motor oil ( overkill!) then if
anneal…if it still cracks you have probably gotten solder and/or
iron or other innocuous contaminants in the mass (files, brass
brushing, solder undetected, etc all add impurities to scrap, as well
s metal that was not tested and acccepted as 14kt. by hearsay- when
the metal was perhaps, plated with 14kt, and perhaps unbeknownst to
the donor!)…

moral:

run a magnet over scrap first to remove any iron alloys, blade bits,
etc. ensure all solder seams are found and removed prior to contact
with your crucible use the 1:2 flux for refining questionable metals
(1part sal ammoniac to 2 parts charcoal - activated and powdered,
NEVER Briquets as used by some in bar-b-queing!!) or when a bright
tough ingot is the desired result…

if it still cracks when rolling, or forging Provided You Are
Annealling Frequently!!! you may have to process with a high acid
formula to literally dissolve the brass, or base metal from the
copper and gold that is 14kt. yellow…( or what ever the colour
UNLESS it’s 14kt. white, then the nickel requires an entirely
different formula for removing it from the gold, or for raising the
karat by adding x amount of fine gold to the scrap to get what ever
karat and colour you are after…write me off list if you need
explanations or further details.

.R.E.Rourke


#3
but how can I know whether this gold has picked up impurities and
are there any ways around the hardness problems, for example can I
try holding the metal at annealing temperatures for many
minutes..... etc.... 

Chris, the problems you’re having are almost certainly due to
impurities or base metals now mixed with your scrap. It can come from
foreign, non gold parts of the jewelry, or most commonly solders,
including low melting tin/lead and other types. There are several
such additives to a gold alloy that will make it almost unworkable,
as you describe, including tin, iron, lead, and others. Sometimes,
just mixing white gold with yellow gold results in unfortunate
ratios of various metals in the alloy resulting in such behavior.

The fix? Well, the real one is to have the metal refined in trade
for new, properly workable metal, but that may not be acceptable for
this use and customer.

But try this. Sometimes it at least helps. Sal Ammoniac, or Ammonium
Chloride, is one of what are called refining fluxes. When added to
molten metals, they facilitiate the removal of undesirable parts of
the metal. Sprinkled onto molten gold, Ammonium Chloride does not
melt to a liquid glaze the way boric acid or borax would do, but
rather, just goes straight to a gas phase. Chlorine gas, mostly. The
chlorine is highly reactive, and will tend to react with metals to
form chlorides. It will do this most preferentially to the most
reactive of the metals in your mix, which are also generally the
undesirable contaminants in your alloy. This pulls these metals out
of the melt, since the resulting metal chlorides are insoluable in
the melt, and instead, mix with the borax (etc) flux, and slag off.
It’s not very efficient, nor will it remove all the contaminants, but
you can sometimes reduce their levels enough to be able to use the
metal.

BE SURE TO DO THIS WITH GOOD VENTILATION. The fumes generated are
toxic.

Ammonium Chloride, as noted above, seems to be fairly effective at
helping trashed gold alloys. But as I said, it’s nasty, generating
some noxious bad fumes. A similar refining flux that’s also a
traditional addition for this purpose, is the less reactive sodium
chloride. Table salt. It too does not melt to a glaze on the melt,
but similarly, helps to pull some of the base metals from the melt.
It’s less effective, but also less noxious.

Using a long anneal on your metal, by the way, will damage it, not
make it more usable. Too cool, and you’ll be age hardening it instead
of softening it. Above the actual annealing temp so it can soften,
doing this for extended times tends to give you grain growth if
you’re above the ideal temperture, and this makes the metal weaker
and more prone to crack. That’s the risk when torch annealing, where
you likely are bringing the metal to at least a low glow, at which
temp annealing is very quick, and extending it doesn’t help. If
you’re doing furnace annealing, so you have precise control over the
temperature, then the best anneals are are what will seem to a bench
worker as too cool a temp, since it’s not glowing, but it’s high
enough to be in the annealing range. Done right, this can give the
least grain growth. But you need some decent data on the proper
temps, or need to hit it by luck. And it sounds like your metal
won’t be fixed just by annealing.

Good luck.
Peter Rowe


#4

In my experience, one of the biggest hazards of working with old
gold is not knowing what the alloy consists of. It sounds as though
someone may have “fixed” the previous item (whatever it may have
been) with lead solder… just a tiny bit is enough to contaminate
the gold and the first sign is the metal cracking when you try to
roll it out… I would refine and start again…


#5

Hi

I have had the same problems, sometimes the only way I’ve been able
to stop the cracking is to add virgin(?) gold, but I’ve also found
that it is very important to add sufficient boric acid to the
crucible when you melt the gold. I assume it keeps the oxidation in
check. I’m not a schooled jeweler, just 40 years of trial and error.
This may have no basis but it has worked for me.

Lainie


#6
gold is incredibly hard and cracks as soon as I try and work it. I
have managed to get some of it down into sheet, but I can see cracks
in the sheet and I'm not sure that it is really of high enough
quality to use! 

There are many reasons why gold might be cracking.

Here is the procedure which should cover a lot of possibilities but
not all.

It would take 2 melts.

Melt your gold with a lot of borax, if you can get saltpeter add to
borax, if not use some table salt. The flux should cover the metal,
use oxidizing flame, pour into water to create small shot. You must
wear goggles during the melt. When adding salt to the melt, the
reaction can be violent, so add little by little.

Collect you shot, pickle if required and wash.

Second melt.

Melt using large but soft reducing flame using only boric acid as a
flux. Be patient because it may take some time to reach pouring
temperature. Watch the metal closely. It will be ready to pour when
metal surface will curve and become very shiny. Flux should retreat
to
the sides when temperature is reached. Pour through flame in steady
even motion. Quench in water and pickle.

You must forge the ingot before rolling. I consider forging is
critical for successful rolling. Forge with peen of the hammer. You
would need at least 300g hammer. What you trying to accomplish is to
break the crystals formed when metal solidified, so forge powerfully
(
within reason ) and cover all area on both sides of the ingot. When
ingot would begin to ring in all places you are done. Anneal it and
roll.

If you still would have trouble, the refining will be your only
course of action.

Leonid Surpin.