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18K yellow gold cracking [S.O.S]


#1

Hello all,

I need to make a diamond engagement ring with 18K yellow gold (alloy
50% copper & 50% silver). The problem is that the alloyed gold
cracks in the mill!! And I can’t help it, it just cracks and cracks.
I’ve tried everything I know, different melting temperatures,
different annealing points, quenching in water, in alcohol, NOT
quenching, EVERYTHING even a saltpetre session, and NOTHING! it just
keeps cracking. I’ve read everything on Ganoksin on the matter, but
there are very contradictory indications. So, I don’t know what to do
anymore.

My rolling mill is a Durston C100, I’ve rolled the ingot very slowly
a very little by little, and quite fast with strong pressure, and
nothing, it cracks. I’m already losing my mind. I’ll appreciate any
help you can give me.

The alloy is an alloy made by me for the occasion, it is virtually
impossible to have contaminated the mix since I was very careful and
clean in the alloying procedure.

I’ll appreciate your help!
Thanks,
Nicolas.


#2

What’s the alloy mix? Regards CIA


#3
The alloy is an alloy made by me for the occasion, it is virtually
impossible to have contaminated the mix since I was very careful
and clean in the alloying procedure. 

Let’s work with the assumption that there is nothing wrong with
alloy, that is chemically speaking.

How about pouring temperature?

Metal should be hot enough to completely fill mold before starting to
set. 3 ounces of gold would require 200 degree plus over alloy
liquidus, and that with pre-heated mold.

Lesser amounts would require even larger temperature buffer. If you
are melting only 0.5 ounce of metal, than better is simply melt it on
charcoal. So size of the melt matters.

Mold size is another variable to take a loot at.

Ideally, metal should completely fill the mold. If filled only
partially, unfilled part becomes heat drain and that results in ingot
stress, which would lead to cracking.

Since we live in the world far from ideal, we have to deal with such
stresses by forging ingot prior to rolling. On my website, there is a
video “Frugal Goldsmith”, which demonstrates ingot forging.

When you start rolling, watch out for edge feathering. If started to
form, it has to be filed off, and deeper cracks should be filed in
with triangular file to stop cracks growing. Rolling must be done in
one direction only. If change of direction is required, ingot must
be annealed.

Ingot should not bent or become wavy during rolling. If it is, it
may indicate unevenness of ingot grain, or problems with mill itself.
Ingot is more likely candidate so anneal it and forge again. Forging
must achieve at least 30% reduction in thickness to be effective. If
problem persist than mill examination is in order.

If you do not know much about mills, I have a write up on my blog,
which will be useful. Especially pay attention to description of
non-homogenious deformation. While it almost an impossibility to
create conditions for non-homogenious deformation with hand-operated
mill, the theory assumes perfect ingot. Since ingots far from
perfect, the non-homogenious deformation could take place much
earlier that theory predicts.

If nothing of the above will help, that assumption of chemically
good alloy, should be reviewed.

If you describe alloy composition and methodology of smelting, we
can discuss it further.

Leonid Surpin
studioarete.com


#4
I need to make a diamond engagement ring with 18K yellow gold
(alloy 50% copper & 50% silver). 

Where did you get the copper? Was some of it from US pennies?

Paf Dvorak


#5

Don’t use any of the newer pennies. They are mostly zinc


#6
Where did you get the copper? Was some of it from US pennies? 

I just go to a metal merchant to buy copper. A kilo goes for about
$8-00 AUD. I’m still looking for a source of tin, as my supply has
dried up :frowning:

America should have a stack of them.

Regards Charles A.


#7
What's the alloy mix? Regards CIA 

Thanks for your answer Charles, The alloy is 7,5gr 24K Gold + 1,2gr
pure Silver + 1,3gr pure Copper.

Regards.


#8

Thanks for your kind reply Leonid!

How about pouring temperature? 
Metal should be hot enough to completely fill mold before starting
to set. 3 ounces of gold would require 200 degree plus over alloy
liquidus, and that with pre-heated mold. 

I did it just as you said.

Mold size is another variable to take a loot at. 
Ideally, metal should completely fill the mold. If filled only
partially, unfilled part becomes heat drain and that results in
ingot stress, which would lead to cracking. 

I use an open ingot mold, those in which the ingot forms
horizontally, and as I used only 10gr of alloyed gold obviously the
metal didn’t fill the mold completely, but the ingot was very even
and sound.

Ingot should not bent or become wavy during rolling. If it is, it
may indicate unevenness of ingot grain, or problems with mill
itself. 
Ingot is more likely candidate so anneal it and forge again.
Forging must achieve at least 30% reduction in thickness to be
effective. If problem persist than mill examination is in order. 

I forged the ingot too, but not to a 30% thickness, I’ll try that.
The ingot DID become wavy, but it happened when I milled it with a
very slight compression and without annealing until 50%-60%
reduction. I thought that the “Wavy” form was a problem, so I did all
the melting again and milled it with a somewhat stronger pressure and
the “wavy” problem was gone.

If nothing of the above will help, that assumption of chemically
good alloy, should be reviewed. 

Well, to be honest, as I waited for some response, I did some
further experiments, and I was actually able to mill the ingot! I
milled it with a cycle of, let’s say, three passes through the mill,
each pass of 0,05mm compression, and then annealed it. As you can
imagine it is quite annoying to anneal that often and THAT much, but
it was the only way to do the work. I have the ring almost done now,
but anyway, I would like to understand what the problem was, so the
next time I can do it the right way.

If you describe alloy composition and methodology of smelting, we
can discuss it further. 

The alloy was 7,5gr gold 24K + 1,2gr pure Silver + 1,3gr pure Copper
(I always like to add a little more copper since I love when the
gold has some yellow/orange color). I melted the 3 metals at the same
time in a crucible which was used only once with 18K gold alloyed by
me too. To assure a good mix I heated the metals to a very bright
yellow color as I stirred the mix, I poured it in the mold and waited
until it was cold, then I melted the gold again but this time not
that hot, I think it was 100deg to 200deg above melting point, then
poured it, and the rest is history: Cracking!

Thanks for your time, I’ll check your site as you suggested me.

Best regards.


#9

From our archives…

Causes and Prevention of Defects in Wrought Alloys
By Mark F. Grimwade, Consultant, Northwood, Middlesex, U.K.

Much of the recent literature on defects that occur in jewellery
manufacture is focused on those occurring in lost wax
(investment) casting, for example reference (1). However, defects
can also occur during casting of ingot and its fabrication into
sheet, tube, wire and rod as well as their onward fabrication
into jewellery components by processes such as stamping and
forging. These defects, along with their causes and prevention,
are briefly reviewed in this article, although those defects
occurring in the die-striking of findings are described elsewhere
in this issue (2). Examples of many defects can be found in the
Handbook of Casting and Other Defects (1), and are referenced in
the text where appropriate. 

Continue reading…

Minimizing Cracks During Jewelry Manufacturing, and Beyond
Peter Raw and Christopher W. Corti

As many jewelry manufacturers and goldsmiths know from hard
experience, cracking in jewelry can occur at any time during its
manufacture. It can also occur much later, after the jewelry has
been sold to the consumer or during repair. Cracking can also
occur in the processing of the starting materials (the casting
grain and mill products from which the jewelry is to be made),
and may not be detected until several stages later in the
manufacturing process. 

Continue reading…


#10
I melted the 3 metals at the same time in a crucible which was used
only once with 18K gold alloyed by me too. To assure a good mix I
heated the metals to a very bright yellow color as I stirred the
mix, I poured it in the mold and waited until it was cold, then I
melted the gold again but this time not that hot, I think it was
100deg to 200deg above melting point, then poured it, and the rest
is history: Cracking! 

The amount of metal is very small. Try to melt it on charcoal block.

Scrape charcoal block so it is slightly concave or metal will roll
off it.

When metal will gather in a ball, just press it with face of old
hammer or something flat. to get the disk. Stainless steel teaspoon,
flattened and bent in convenient angle works very well. It is also
good idea to cover copper with borax before melting. Melt it twice.
When you get your first disk, roll it very thin. Ignore the cracking
if it happens. Shred thinly rolled alloy with snips like you do
solder and melt it again. This is necessary to insure good mixing of
metals.

Leonid Surpin
studioarete.com


#11
The alloy is 7,5gr 24K Gold + 1,2gr pure Silver + 1,3gr pure
Copper. 

That mix should be okay, you could try another mix.

All components should be by weight.

7.5 g Au + 12.5 Ag + 12.5 Cu

7.5 g Au + 1.6 Ag + 0.9 Cu

Load your crucible in order with the lower melt point metals first.

Melt and pour into your prefared ingot mould.

Let us know if the ingot still cracks.

Regards Charles A.


#12

Leonoid - Thank you, for the great

I just watched your youtube video from the “Frugal Goldsmith” It was
great, but I have a question or two.

If I am melting on a charcoal block does it matter which direction I
forge? Is there a way to tell which way the grain is going?

Did you anneal every few passes to get that gorgeous gold sheet, or
was that after your initial forging process and annealing just the
one time?

Thanks again!
Robyn


#13
Load your crucible in order with the lower melt point metals
first. 

Strange advice!

In this particular case it would mean, - silver going into crucible
first, then gold, and copper will be on top of crucible. So the most
susceptible metal for oxidation is put in position where chance of
oxidation is the highest.

To make better use of crucible loading scheme, - put copper on the
bottom, silver in the middle, and gold on top.

Even better is to roll copper very thin, fold it into neat package.
Roll silver very thin and wrap copper with it, making package of
silver with copper inside.

Finely, roll gold very thin and encase silver package with gold. Now
we are ready to melt.

Leonid Surpin
studioarete.com


#14

Hi Charles

I have a supplier in Brisbane for tin. Sounds like your in ozz?
Message me for address etc.

Regards Phil


#15
If I am melting on a charcoal block does it matter which direction
I forge? Is there a way to tell which way the grain is going? 

If objective is to obtain flat sheet, after metal is molten and
balled up, flatten it with something suitable. Old hammer works fine.
I do not mean to hit it with a hammer, just gently press it for
desired thickness. In this case there are would not be uniform grain
direction. For forging purposes pick one you will be rolling along
and forge 45 degrees towards it.

If objective is to obtain wire, instead of using hammer, gently
squeeze the ball of molten metal with tweezes. With some practice, a
nice rectangular ingot will result. In this case the grain direction
will depends on so many variables that it is not possible to
predict. Small ingots for wire production, do not require any
forging.

Did you anneal every few passes to get that gorgeous gold sheet,
or was that after your initial forging process and annealing just
the one time? 

Annealing is one of those question where it is difficult to give a
straight answer.

Generally, the less frequent it is, the better. Theory says that one
should achieve 70% of deformation before annealing ingot. It may be
possible with perfect ingot and huge industrial mills. I could never
do it. What it means in numbers is that from 4mm thickness to 1.2mm
without annealing. I try to stick to 50% deformation. So if I start
with 4mm annealed ingot, I roll it to 2mm, anneal, and roll to 1mm,
and etc.

That said, if you feel that metal needs more frequent annealing,
than do what it requires.

Over-annealing could damage alloy, but so is over-working. If alloy
becomes unyielding, it is better to take a chance on over-annealing
than on over-working. So general rule can be stated as - anneal as
little as you can get away with.

Leonid Surpin
studioarete.com


#16
Strange advice! In this particular case it would mean, - silver
going into crucible first, then gold, and copper will be on top of
crucible. So the most susceptible metal for oxidation is put in
position where chance of oxidation is the highest. 

Different advice, is a better word for it.

I always load my crucibles with the lower meltpoint metals first,
it’s more efficient to melt this way, you use less energy to melt
your charge.

Mind you I melt in a furnace, I use fine granulated copper, I’m not
melting directly with a torch, and I definitely don’t use oxygen in
my furnaces. No oxygen means no platinum family, but I don’t like
platinum, so it’s not an issue for me.

When you melt this way, the copper forms a crust, sealing the
crucible, protecting the lower melt point metals from oxidisation and
vaporisation.

I repeat there’s no oxidisation with this method (unless you boil
the charge, and you’d be a fool to do that).

Regards Charles A.