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Overheating Yellow Gold


#1

This is off the subject, but Peter Rowe a while back gave
temperatures, colors and times for annealing gold. He wrote that
yellow gold should be heated only to dark brick and immediately
quenched. Previously, following some threads in the archives I had
found that one should either heat gold up to orange for 30 seconds
or 30 minutes so had sort of split the difference, to my regret
because cracks invariably formed on rolling out. My question is,
once yellow gold has been overheated, is it possible to start again
and make another ingot or does the gold have to be sent off to a
refiner. It is only about half an ounce so…

Peter Schneider
@Peter2


#2
 following some threads in the archives I had found that one should
either heat gold up to orange for 30 seconds or 30 minutes so had
sort of split the difference, to my regret because cracks
invariably formed on rolling out. My question is, once yellow gold
has been overheated, is it possible to start again and make another
ingot or does the gold have to be sent off to a refiner. It is only
about half an ounce so.. 

Peter, overheating the metal during annealing causes the crystal
structure to grow in crystal size. That metal, with large crystals,
is not then as strong as when one anneals correctly. But it should
still be workable, just as you can roll a newly poured ingot, which
may also have unevenly sized or larger crystals. If you’ve got
cracks forming unduly, try less of a reduction between annealing.

If this still doesn’t work, then re pour the ingot. Over annealing
by itself shouldn’t cause such harm to the composition of the metal
as to require refining. Be sure, when you melt the metal, that you’re
not overheating the melt, and that you’re using a proper flame
(usually slightly reducing is what you want) as well as suitable
melting fluxes.

Now, if in originally pouring your ingot, you mixed in foreign
materials, or heated the melt so hot that you volatilized some
components of the alloy, you might have significantly altered the
working properties. I’ve had some white golds in particular, that got
contaminated in some unidentified part of the process, and which I
simply could not get to roll or draw out at all. So it’s

But I’d suggest you first try just re pouring the ingot and rolling
again. Note that it’s not all that unusual to have a few bad spots in
an ingot. We all get them. Often one can just work around them, or
trim them off as they become apparent, and continue rolling or
drawing. With Yellow golds, they are often more salvageable than
white golds or platinum if you’ve messed up the alloy.

It can help to melt the metal in a hollow carved in a charcoal
block, and in addition to using normal borax or boric acid flux, add
a little bit of ammonium chloride after the metal is fully melted. It
will skitter around the surface of the metal for a moment, then is
gone, at which point you pour the ingot. The ammonium chloride is a
"refining flux", which is able to bond with some baser metals in an
alloy, forming metal chlorides. In general, these are insoluble in
the melt, and slag off. The components mostly affected are those
which are most reactive, so the ammonium chloride can help remove or
reduce the amount of such contaminants as tin, iron, or the like,
from your melt should these have gotten in there by accident. And
the charcoal block combined with a reducing flame and your melting
flux will do a good job of greatly reducing any dissolved oxides in
the melt.

If melting on a charcoal block to clean up “dirty” metal, I usually
melt it till it’s a clear liquid pool, then add more borax/boric acid
mix (I use a 50/50 mix of the two) to form a glaze over the button,
which is left on the block to solidify because it’s harder to pour
cleanly off a charcoal block. When solid, it should then be clean
metal, to be transferred to your normal pouring crucible and the
ingot poured. The charcoal block may be overkill, but on some
occasions I have it salvage a bad piece of metal, in conjunction with
the ammonium chloride.

Also, you may find that if you’re using an open faced ingot mold,
your metal will be more prone to crack than if you use a closed
mold. The type with two sliding plates that pours either an
adjustable width flat ingot, or with the plates reversed, one of
several sizes of round rod, is my favorite type of ingot mold. Ingots
poured in these are a lot easier to get to roll out without cracking,
than the variable thickness, oxide damaged surfaces, on the ingots
poured into open rod or plate molds.

Hope that helps.

Peter Rowe


#3

What karat yellow gold are you working with? What Alloy? How much
cold work have you given it between anneals? You cannot just use a
generic “anneal yellow gold at a brick red” and hope for optimum
results. Contact your metal supplier for correct temperatures for
the alloys you are using.

Over annealing causes an enlarged grain structure that as you have
found results in reduced strength of the crystal matrix and can
lead to “orange peal” surfaces or structural failure of the
material.

Torch annealing is probably the worst way to anneal metal. It is a
non uniform heat source and temperature control is basically
nonexistent. A trained eye can only be a so so judge of temperature.
It is very subjective and depends a lot on the ambient light
conditions ( Light source , incandescent? florescent? sunlight? a
combination? how bright?) If you must anneal via torch then use a
temperature indicating crayon or paint ( they melt at specific
temperatures ranging from 200F to 2200F ) at least often enough to
get and keep your eye “calibrated”.

You will however achieve a much more through anneal if you use a
temperature controlled kiln for your annealing and do it at a lower
temperature for a longer period of time (15-30 min ). You will be
amazed at how much softer and more workable your metal is if you
kiln anneal at the right temperature for a long enough time.

It is also very important to put enough cold work into your metal
before annealing. If you have not significantly reduced the
materials section by drawing or rolling or changed its form through
forging or raising you also run the risk of excessive crystal growth
when you anneal just as if you annealed at too high a temperature.

Jim

Jim Binnion

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160


@James_Binnion
Member of the Better Business Bureau


#4

After all that I forgot to answer the basic question :frowning: Typically
if you have over annealed the metal it is very difficult to save it.
The only way to fix it is to get a significant amount of cold work
into it to break down the large crystals. Unfortunately this will
often result in the metal being too thin or it may crack at the
grain boundaries while working it.

Jim Binnion

James Binnion Metal Arts
Phone (360) 756-6550
Toll Free (877) 408 7287
Fax (360) 756-2160


@James_Binnion
Member of the Better Business Bureau