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Annealing 24K, 22k, 18k Gold


#1

Hi All – I know this is the right group to go to for help!! I have
been hooked on chasing & repousse for the last year + (thank you
Valentin Yotkov!!). To date, all of my work has been in copper,
sterling and fine silver (with one small piece in 14k gold). I want
to move into gold (Valentin’s recommendation is to work in 22K). My
work with / use of gold in the past has been minimal – soldering
decorative accents, sizing rings, adding it as a component of a
married metal piece, etc. It is necessary, in repousse, to anneal
the entire work at least once in the process, and I’m not sure what
exactly to look for and whether there is a particular strategy to
heating the piece effectively that is different from other metals.

First off – do I use the same kind of flame that I use for
annealing silver or copper ?

My reading about the correct temperature seems contradictory – and
I’m thinking this is because how you heat gold depends on what
process you want to accomplish. (??) The Revere book indicates in
a table that 200 C is what you look to achieve for fine gold;
Brepohl on the other hand states that gold needs to reach a minimum
temperature of 400 C. I’m assumong there is a reason for these
differences that I just do not understand.

All my reading seems to indicate that the shortest possible time at
the right temperature is the best. What about quenching? I have
read that cold water right away is best and have been told that
denatured alcohol is better as it causes less stress on the metal.
Does it make a difference? Do you quench right away or wait 10 or
20 seconds?

What about pickle – is standard pickle the best thing to use –
and here I’m speaking generally more about the lower karat golds –
those that have more copper – will standard pickle lessen the
"rosey glow" that you can get?

Any help will be appreciated – thank you so much for your help –

Laura Wiesler
StoneHouse Group


#2

First you need to distinguish between theory and practice. Various
books will tell you various things (The one about quenching in
alcohol is a new one on me—) Basically, for 24, 22, and 18 Kt
golds, if you treat it in the way you have been treating copper (as
fas as flame type and annealing temp), you will be OK - get denatured
alcohol (methanol is better, but harder to get) and put a little more
boric acid in it than will dissolve- it acctually works better after a
few hours, or the next day. This is the standard thing that
goldsmiths use to coat gold before heating- dip in your piece, light
it on fire to burn off the alcohol, and it will be coated with high
temp. flux. Annealing is a curve that is a function of time and
temp. You can actually, theoretically, anneal silver by having it at
250c for 24hrs - not real numbers, but that is the idea. It is better
to hold metal at a more moderate temp. for a few minutes (platinum,
for sure), than to “fry” it. There are people who have specific
needs from metal - hardening, tempering for exact purposes. For
them, these issues mean a lot. To do generic metal in a generic way,
I have annealed all precious metals, let them lose their red, and toss
them in the quench, without any ill effects, for 30 years, 8-16 hrs.
a day. Bottom line: Overheating is what will get you—The grain
stucture falls apart, and the metal is scrap…


#3
(The one about quenching in alcohol is a new one on me---) 

The alcohol quench is simply a gentler quench, cooling the metal a
little less quickly. It’s useful for those metals that lack strength
at annealing temps, and which might crack from the stresses of overly
rapid cooling. Nickel based white golds and rose golds are the two
main ones that come to mind. That’s not to say you can’t quench
these in water too. It’s just that doing so is a little riskier,
since if you quench from too high a temp, you can get cracking,
especially in cast pieces or thick sections, or pieces with both
thick and thin sections in close proximity. Quenching from
sufficiently cool temps will prevent such cracking, but then you run
the risk of quenching from a low enough temp that the metals may have
had a chance to start age hardening a bit, so then you don’t get a
fully soft anneal. 18K red golds especially can be tricky, since
below about 750F (I think. might have to look it up), they can go
through a phase shift to an ordered array structure that is
exceedingly brittle, and you need to cool these alloys through that
temperature range quickly enough so they cannot form that structure.

Peter


#4

Dear John

       ....  You can actually, theoretically, anneal silver by having 

it at 250c for 24hrs - not real numbers, but that is the idea. I
think you are absolutely wrong here. When I want to age harden silver
I normally put it in the kitchen oven at max. which is about 250
degr. C for 3 - 4 hours. It works for me as a hardening proces. I
think I had the idea from either Tim McCraig or Untracht. Once I
forgot the oven for about 14 hours which gave an even slightly harder
result. Regards from sunny Bornholm, Denmark, where the wild cherries
are in full blossom. Niels Lovschal


#5

How can you tell to quench metal when it’s reached the appropriate
750 degree temp?

Elaine Luther


#6

There is a process called age hardening that works for sterling
silver. To get the full effect you must heat the sterling to 750C
for about 30 minutes then rapidly quench this is called solution
treatment. Then age it at 300C for 1 hour. While several jewelry
texts talk about the aging part they often omit the solution part of
the process and without the solution treatment you will get little
increase in hardness. The main drawback to this process is that 750C
is above the melting point of silver solders so it only really works
for non soldered parts . If you age harden and then solder on it it
will anneal it and negate the aging process. So it works great for
things like flatware but is of little use for other items unless
you use cold joining techniques.

Jim


#7

The one about quenching in alcohol is a new one on me

I was taught, to quench in water; it’s safe, no splatter and no
unsafe fumes, and then pickle…quenching in water sounds like a
sure-fire way to cause a fire. Reminds me of the time that someone
applied an alcohol prep to a dog’s skin then proceeded to use
electrocautery to remove a blemish. There was a fire, a law-suit and
a lot of smirks from others inside the profession.

“I remember your eyes were bluer than robins’ eggs. My poetry was
lousy you said. Where are you calling from? A booth in the midwest”


#8
quenching in water sounds like a sure-fire way to cause a fire. 

You mean, quenching in alcohol…

it does now and then light the alcohol if you quench from too hot,
but it’s actually pretty rare that this happens. The metal should no
longer be glowing at all when you quench. Around 900 F or so, or a
bit less. At that temp, it won’t ignite the alcohol. Also, the
metal at that temp doesn’t actually contact liquid alcohol. It does
the same thing it would do if it were quenched in water. It creates
a layer of vapor around it, and the initial cooling is from the vapor,
not the liquid. Alcohol forms a vapor more easily, and so absorbs
heat in the process more slowly than does water, thus the gentler
quench. When you quench, don’t slowly dip it in. Immerse the piece
all at once. That’s more even cooling than a slow dip. The same
goes for a water quench by the way, or oil. Once the hot piece is
under the liquid, It cannot ignite anything, since there’s no oxygen
there, just the alcohol, and by the time bubbles of the vapor reach
the surface, they’re pretty cool again.

But the main thing is to use a jar, not an open dish. this way, the
access to the liquid, of oxygen/air, is somewhat limited, and more
easily controlled if needed. Alcohol fumes are flammable, but not
especially explosive, at least not in this situation. So when you
accidentally set the jar on fire, it’s a slow gentle simmering flame,
not some sudden catastrophic fire. And the solution is simple
enough. Put the lid on the jar. And don’t get startled into
knocking over the jar!

It’s common practice for goldsmiths to have a jar of a mix of boric
acid and alcohol on their bench for use in fire coating gold and
platinum, especially pieces containing diamonds, which will be heated
or soldered upon. Since in that use there’s usually an open flame
around (one’s torch), the alcohol cup now and then gets set on fire
by the torch too. Same deal. no big problem, so long as you don’t
get startled and drop the jar and spill it’s burning contents all
over… I’ve done that only once, a number of years ago, when for
some reason the jar cracked in half and all the alcohol flowed into
the bench pan to burn. Even then, it’s not a total catastrophe, just
a mess. I laid a wet towel over the burning area, and the fire went
out. simple enough. But I then had to clean up the mess in the
bench pan.

Peter


#9

Peter et al,

I have been working on the bench for well over thirty years.

After about ten years on the bench, having gotten used to using a
large mouth container of alcohol and boric acid set the jar on fire
as I had probably done a hundred times before. I was putting the jar
down when I felt a burning sensation on the webbing between my thumb
and forefinger. Shouldn’t have been anything to panic about, but in
my haste to put the jar down gently, I managed to bump into my tray
or something and spilled it … hmmm … how you say all over my
stomach and chest? Yah, now I had done it. In about the time required
to say Yikes! I was rolling on the floor.

I burned at least three layers of flesh from the back of my hand.
Anyone that has has such a burn knows that this does not heal from
the inside. It heals from the edges in as healthy skin is required
grow new skin. I don’t remember exactly, but it was 7 to 9 monthes
healing.

The purpose of the alcohol is to act strictly as a carrier for the
boric acid. I am not even sure that boric acid is even soluble in
alcohol. Ever since, I have been using boric acid powder without the
alcohol. I just dip my work in finely divided boric acid powder and
it is coated. I don’t have to wait 'til the flames go out. Works
fine. I no longer get to watch a pretty green flame, but guess what.
I don’t miss it.

This account is in the archives, but I hear so many people that
worry about the “toxicity” of pickle turn around and suggest that we
should handle open containers of rocket fuel around open flames that
I have just gotta share my experience again and again.

bruce d holmgrain
JACMBJ


#10

Hi Gang,

Also, the metal at that temp doesn't actually contact liquid
alcohol.  It does the same thing it would do if it were quenched in
water.  It creates a layer of vapor around it, and the initial
cooling is from the vapor, not the liquid.  Alcohol forms a vapor
more easily, and so absorbs heat in the process more slowly than
does water, thus the gentler quench. When you quench, don't slowly
dip it in.  Immerse the piece all at once.  That's more even
cooling than a slow dip.  The same goes for a water quench by the
way, or oil. 

To add a little something to Peter’s reply (It’s not often he
leaves anything out!). I’ve never done a study to see what the effect
is on the size pieces used in jewelry, but in the ferrous metals it
makes a difference. Peter may have said it all anyway.

In addition to thrusting the piece into the quenching liquid,
instead of lowering it slowly, move the piece around with a figure 8
motion. This keeps exposing the piece to cooler quenching liquid &
results in a more even temper in the piece.

Dave


#11
the jar cracked in half and all the alcohol flowed into the bench
pan to burn

This is why I favor a plastic peanut butter jar. Then if you get
what I like to call “flux flambe” and you smother it with a lid, the
contraction of the air inside when it cools sucks the softened
plastic into a whole new, interesting shape… but no breaking.

–Noel


#12

Bruce, What makes the boric acid stick to the metal?

Marilyn Smith


#13

Hi, Forgive the iggerance of a foreigner but what exactly do you mean
by ‘alcohol’? Are you referring to ethanol, methanol, propanol or
what? Is it maybe what we know as ‘methylated spirit’ - methanol with
a dye added?

Best wishes,
Ian
Ian W. Wright
Sheffield, UK


#14
   Hi, Forgive the iggerance of a foreigner but what exactly do
you mean by 'alcohol'? Are you referring to ethanol, methanol,
propanol or what? Is it maybe what we know as 'methylated spirit' -
methanol with a dye added? 

Ian, If you’re wondering about references to an alcohol quench, then
at least one answer to your question above, would be just “yes”. But
most of the time when we’re buying alcohol here in the states for
jewelry use, it’s “denatured alcohol”, which is easily available
cheaply in the hardware store, usually in the paint section, where
it’s sold as a shellac thinner, and for other uses. It amounts to
mostly ethanol, but with enough of something else that’s toxic,
usually methanol, added so it cannot be consumed as a beverage. But
so far as I know (though i’m not a chemist), for uses such as mixing
with boric acid in order to fire coat gold/diamond jewelry for
soldering, or for quenching certain gold alloys, there’d not be much
difference between ethanol, methanol, or your methylated spirit. I’m
not familiar with propanol, so can’t comment on that one.

Peter


#15
What makes the boric acid stick to the metal? 

who said it actually does? Mostly, it’s just sitting there, perhaps
held on with enough surface tension, or traces of residual moisture,
etc. When you burn off the alcohol, it leaves a thin film of boric
acid, which is often then like a light dusting of powder, which can be
easily wiped or brushed off once it’s fully dry. but it still sticks
well enough to stay there while you heat it, and once you start to heat
it, it melts onto the metal.


#16
     This account is in the archives, but I hear so many people
that worry about the "toxicity" of pickle turn around and suggest
that we should handle open containers of rocket fuel around open
flames that I have just gotta share my experience again and again. 

A sobering story Bruce. Glad you survived…

for my part, though I still use boric/alcohol, since I feel it’s
better at evenly distributing the mix even to hard to reach areas, I
have changed early carefree handling methods. Now, when I’m doing
anything with a flame nearby, I don’t pick up the alcohol jar. It
stays firmly sitting on the benchtop, away from the edge.

Peter


#17

Hi Ian,

Is it maybe what we know as 'methylated spirit' - methanol with a
dye added? 

That’s most likely what it’s called in the UK. In the US, it’s
usually called ‘denatured alcohol’. It’s methanol to which a poison
and usually a purple dye is added. The purple dye is added to
differentiate it from other alcohols. Consuming denatured alcohol can
cause blindness & even death according to the warning on the
containers.

Dave


#18

Hi, Dave – just to clear up a little confusion in alcohols here. –
Methanol (“wood alcohol”) is poisonous to begin with – it does
not need to be denatured to make it poisonous. Ethanol (Grain
alcohol") is the one that needs to be denatured. And denatured
ethanol is what you should best be using, since Methanol can actually
be ingested through the skin (especially if you have a few cuts,
etc.) – you don’t have to drink it – to cause blindness; you
don’t want to be using something that you don’t want to (even
accidentally) get on your skin.

Margaret