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Gold tarnishing


#1

Hoping someone out there might be able to help me. I have a caster
who is using a greenish colored yellow gold. The castings have a
tendancy to weigh more than the calculated weight (from the wax
weight) but most annoying is that the gold is turning color. Its
embarrassing when customers complain and the tarnish is not just
where the piece touches the skin but even on top well away from the
skin. There is no discoloration on the wearers skin. It even happens
on pieces in the showcase. Basically, my question is What would be in
the alloy to make it turn and weigh more. Being a greenish-yellow it
has a high silver content and fine silver shouldn’t tarnish. The
caster buys the alloy prepared and mixes it with the gold himself.
Any help would be appreciated. Thanks in advance Lee


#2

sounds like you have a very high copper content in your alloy. can
you ascertain the actual percentages of the components?

john


#3

Sounds like someone let some gold filled material get into the scrap
and/or is using a master alloy with no real gold in it. That would
explain the weight issue-using a green gold alloy but 'forgetting’
that the alloy needs to be karated. It could be a copper free alloy
which would explain the absence of skin reaction, and in the case
anti-tarnish tabs would protect any silver from turning. gold doesn’t
tarnish so it seems that its a contaminated crucible with cupric
oxides which would affect any metals other than gold in the melt, or
just master alloy with no gold, or gold filled used in place of the
karat gold (and that gold in the correct karat and colour for the
weight you were expecting even though you have to allow some
tolerances for sprueing, etc.) to cast the piece(s).It would have had
to be a large piece of ferrous metal to make such a difference in
weight if everything else was done correctly .I’m still betting on
all green alloy or a crucible contaminated with oxides and the entire
lot being poured with no karat gold added. rer


#4

Have you tested the gold content yourself? Just use an acid test kit
to determine the gold content.

If the gold content is up to scratch the ask the caster what the mix
is, if he wont tell you get an independent test.

Regards Charles A.


#5

Hi Lee

very interesting, I am a goldsmith not a metallurgist. Metallurgists
may be able to explain what is happening.

To me it sounds like a bad mix of low karat gold. This is why I use
tried and true casting companies.

Get a new caster and replace all stock you sold as the problem will
keep happening as your customers go elsewhere.

Send it back to the caster and get a full refund. Consumer law will
back you on this.

Richard


#6
Hoping someone out there might be able to help me. I have a caster
who is using a greenish colored yellow gold. The castings have a
tendancy to weigh more than the calculated weight (from the wax
weight) but most annoying is that the gold is turning color. 

You probably are not using the right specific gravity numbers or the
waxes may be shot at too high a pressure and end up oversize.

Its embarrassing when customers complain and the tarnish is not
just where the piece touches the skin but even on top well away
from the skin. There is no discoloration on the wearers skin. It
even happens on pieces in the showcase. Basically, my question is
What would be in the alloy to make it turn and weigh more. Being a
greenish-yellow it has a high silver content and fine silver
shouldn't tarnish. The caster buys the alloy prepared and mixes it
with the gold himself. 

Fine silver certainly does tarnish and all gold alloys can tarnish
in the right conditions. Very often the display case has just the
right conditions to cause it. Off gassing from the display materials
and UV radiation from halogen lights can do horrible things to many
metals. For more info on gold alloys tarnishing see this article by
Dr. Christopher Corti who before his retirement worked as a senior
technical advisor and consultant for the World Gold Council.

James Binnion
James Binnion Metal Arts


#7
Have you tested the gold content yourself? Just use an acid test
kit to determine the gold content. 

This problem of gold tarnishing showing up from time to time.

The answer is still the same. I have written about several times
before, so I am not going to repeat it again. In a nutshell, in order
for an alloy to have gold properties, gold must be dominant
component. 14k gold simply is not this type of alloy.

Leonid Surpin
Studioarete.com


#8
Have you tested the gold content yourself? Just use an acid test
kit to determine the gold content. 
If the gold content is up to scratch the ask the caster what the
mix is, if he wont tell you get an independent test. 

While a test is a good idea, but if they are coming in at or over
weight it is very likely they are at karat.

James Binnion
James Binnion Metal Arts


#9
To me it sounds like a bad mix of low karat gold. This is why I
use tried and true casting companies. 

If it is at correct or slightly over weight it is unlikely it is
below karat. There is just not much that can be added to the gold to
make the weight come out at or above what it should be. If it was
under weight that would be a different story.

James Binnion
James Binnion Metal Arts


#10

Where I work, we have found that 14k green does tarnish. We try to
encourage clients to go for 18k if they want green. I presume it’s
all that silver in there.

Noel Yovovich


#11

My concern is that the person mixing the alloy either has a problem
with his procedures, and of course we have to rule out the shonk
factor.

If it’s a problem with his procedures, then that can be fixed. If
it’s the shonk factor then it’s time to get the law involved.

Regards Charles A.


#12

Lee, in my reply I meant fine gold does not tarnish. I guess I
didn’t re-read the copy before hitting send. sorry…


#13

I’ve used 18 and 14 karat green gold in my work using wire and
casting grain from Stuller and Hoover that I cast myself and castings
from well regarded casting houses and I can tell you that in addition
to being a soft metal that doesn’t work harden, it’s also prone to
tarnishing. That’s the nature of the metal.

Polished 18 wasn’t problematic, but any kind of non polished texture
on 18 green, whether it’s added or on a remaining raw surface from
casting, it will tarnish over time. Textures I’ve used include
lightly brushed matte, heavy grit sandpaper, fine and coarse
sandblasting and stippling. There are environmental factors that will
hasten the effect, like cigarette smoke and exposure to LOS, but even
in normal conditions, over time textures and areas not exposed to
wear in 14 kt green alloys will tarnish.

A single cycle in an ionic cleaner removes all traces of color. The
plus side is that after the piece goes through several
tarnish/stripping cycles, you’ve in essence created an enriched gold
layer that is much more resistant to tarnishing.

Since gold prices increased I no longer make these prices, but the
color was really beautiful and contrasted well against yellow, red
and white gold.