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Interesting alloy question


#1

was: Anyone make their own solder?

Hi Richard,

the fine gold torcs also 'work harden' over time and become
brittle. Of course if they were 18 kt the copper would be attacked
by the elements. What if the copper had been replaced with fine
silver for 18 kt? 

Honestly I don’t know, but I’m going to go for a stretch, I would
think that there would be a galvanic reaction even a minimal
reaction.

Regards Charles A.


#2
Okay, I will bite. How is it determined that an alloy with less
than half of the atoms being gold will have none of the properties
of gold and an alloy with half or more has some of the properties
of gold? 
Simple answer. Chemistry! 

Sorry, but your simple answer it just too simple. Specifically what
property of gold is the same with “18 Karat gold”? Could it be…

Specific gravity
Color
Hardness
Reaction to acids
Melting temperature
Electrical conductivity
Thermal conductivity
Specific gravity

Perhaps, there are no “chemical properties” of “18 karat gold” that
are thesame as gold. Perhaps the reason why “18 karat gold” is used
to make jewelry is because the properties of “18 karat gold” make it
a more attractive metal than gold for this purpose.

In other words, 18 karat gold is different from gold in every way,
just as 9 karat gold is.


#3
the fine gold torcs also 'work harden' over time and become
brittle. Of course if they were 18 kt the copper would be attacked
by the elements. What if the copper had been replaced with fine
silver for 18 kt? Honestly I don't know, but I'm going to go for a
stretch, I would think that there would be a galvanic reaction even
a minimal reaction. 

you need an acid to make a galvanic reaction- so that theory doesn’t
work. and if in an 18 kt gold - lets use yellow or red for examples-,
replacing the copper in the alloy with fine silver would yield a
different alloy altogether from 18 kt in fact what you would have is
a basic green gold- 75% yellow/fine gold grain and adding the balance
in fine silver (25%) So, you can take the copper out of the formulae
but its going to be a different colour or karat There is a metal
called Electrum which is 1:1 gold to silver, this is closer to a 14
karat alloy though, but not exactly… (53,5% qualifies it) What you
would get is not exactly that either since its half and half…18 kt
is roughly 3 parts fine gold to one part copper or palladium/Pt or a
mixture of metals in an alloy to give it colour firstly, tensile
strength after that. most manufacturers are after colours, not
strength bering alloys in the small shop! again, not sure what it is
you want to do, or know…


#4
fine gold torcs also 'work harden' over time and become brittle.
Of course if they were 18 kt the copper would be attacked by the
elements. 

Just an interesting perspective, getting away from the silliness. I
had a simple setting job to do for a professor of archeology from
Berkeley some years ago. The quintessential professor, kindof an odd
duck but a real nice man who just didn’t get out much. Wehad some
conversations and in one of them I said that there were something
like a million people in Europe in the Middle Ages and every oneof
them had a spoon and a cup. Then there were another million and
another and another, so that means there were like a billion spoons.
So, where are all the spoons? Not to mention the cups. Not a new
idea but it’s good to remember these things. Only the gold survives
the march of time - the looooooong march of time, that is. It
doesn’t mean that people didn’t use copper or silver or other alloys
of gold over history, it just means that it hasn’t survived to this
day. All the spoons either rotted, corroded, were burnt or melted or
all manner of thingsthat people do with cheap spoons. It’s the 200
year rule of antiques. There’s this and that to be found until about
200 years back and things start to get really, really scarce except
for some really special items. They just don’t survive that long, by
and large.


#5

Hi guys,

I’ve always heard that really old non-ferris metalwork anneals over
time, and is generally shockingly soft.

(old meaning more than 1500 years old)

Anybody know more than that?
Regards,
Brian


#6
In other words, 18 karat gold is different from gold in every way,
just as 9 karat gold is. 

If you go to the very beginning of this subject, you should see that
I said that alloy is starting to exhibit some properties of gold when
at least half of it’s atoms are gold. I also emphasized that not all
the properties but some!

For jewellery work mechanical properties of gold, which we are
loosing by alloying it, are not desirable anyway. What we want are
color, reflectivity and resistance to corrosion. And these only begin
to resemble gold when at least half of the atoms are gold. Properly
formulated 18k satisfies the requirement, anything less does not !
And if you want to understand how important the color is, - here is
the subject to research.

Why paintings are always framed in gold ? You can go to any museum to
verify this. Because color of gold improves saturation of other
colors.

NO OTHER COLOR HAS THIS PROPERTY !

And saturation is a lot of money in jewellery. Just price some
gemstones like emeralds graded 3 versus 4, in GIA nomenclature.

That is why colored gemstones must be only mounted in 18k yellow
alloys.

It is extreme silliness to mount them in anything less. The apparent
loss of value is far exceeds “savings” of using lesser alloys. And
for me, the most remarkable thing that I learnt from this discussion,
is that some jewelers, claiming a lot of experience, are completely
unaware of this simple fact. The most important commandment in
goldsmith’s bible is never to suppress appearance of a gemstone.

Leonid Surpin
Studioarete.com


#7

How different is different?

SG? the SG of 18k is about 15. How many alloys or elements have a
higher SG-not many Colour- you need to refer to its colour and
reflectance as expressed in the determinative tables for reflected
light microscopy. Small differences.

Hardness? what is the difference between the 2 as both a percentage
and an absolute. small differences on VHN compared to range of
possibilities.

Reaction to acids? which acids- no reaction to anything other than
conc nitric and aqua regia for 18k so can you say that the lack of
reaction to HCl or H2SO4 isnt any different.

Melting point. this probably has the biggest range according to what
the 18k alloy actually is as you could include solders with this
one.

Conductivity? again the absolute difference is small with both
electrical and thermal conductivity.

We really need to consider the differences as relatives, ie pure
gold is softer than 18k, 18k has a lower melting point than pure gold
and so on as it is these relative differences that make our tasks
easier and hopefully more interesting as we can apply our skills in a
way that would be impossible (or damned difficult) with pure gold.

Nick Royall


#8
you need an acid to make a galvanic reaction- so that theory
doesn't work. 

No, just an electrolyte so salts which are abundant in the
environment will work just fine in combination with water to create
the galvanic reaction.

James Binnion
James Binnion Metal Arts


#9

Hi Leonid,

That is why colored gemstones must be only mounted in 18k yellow
alloys. It is extreme silliness to mount them in anything less.
The apparent loss of value is far exceeds "savings" of using lesser
alloys. And for me, the most remarkable thing that I learnt from
this discussion, is that some jewelers, claiming a lot of
experience, are completely unaware of this simple fact. The most
important commandment in goldsmith's bible is never to suppress
appearance of a gemstone. 

Yes. That would be why Winston’s mounted the Hope diamond in
platinum. Twice.

Regards,
Brian


#10

In my thoughts. the only reason alloying gold came about was for
three reasons…1 alloyed gold allows you to change the color…2
makes it harder so better for holding stones and resisting wear. And
3 drops the price to where the masses can afford to say they have a
piece of gold jewelry…

This should about cover this subject unless I have missed a point
which on occasion I do…

Make lots of jewelry and. sell lots of it so yoy can make more…


#11
Why paintings are always framed in gold ? You can go to any museum
to verify this. Because color of gold improves saturation of other
colors. 

Sorry Leonid, that’s not true, some paintings have gold mouldings,
but it really depends on the colours the artist has used in the
painting.

I’ve just left the employ of the art shop/framers shop, and am now
counter sales selling jewellery equipment (all the projects,
jewellery and otherwise will have to wait for after hours). We framed
some paintings in gold, some in scratched silver, some in wood etc.
It’s very much the colours of the painting that dictate what frame to
use.

If you are talking about heavy old masters, some of those are suited
to heavy gold ornate frames, but not all.

And saturation is a lot of money in jewellery. Just price some
gemstones like emeralds graded 3 versus 4, in GIA nomenclature. 
That is why colored gemstones must be only mounted in 18k yellow
alloys. 

Again I think it depends on the stones colour, sure a citrine is a
relatively inexpensive stone compared to a natural emerald etc. My
opinion is that a citrine has a greater contrast when set in a
white-ish metal, like platinum.

It is extreme silliness to mount them in anything less. The
apparent loss of value is far exceeds "savings" of using lesser
alloys. And for me, the most remarkable thing that I learnt from
this discussion, is that some jewelers, claiming a lot of
experience, are completely unaware of this simple fact. The most
important commandment in goldsmith's bible is never to suppress
appearance of a gemstone. 

I wouldn’t say silliness, platinum gives a better contrast to some
coloured stones than gold does, it depends on the colour of the
stones, and the preference of the customer.

Regards Charles A.


#12

you need an acid to make a galvanic reaction- so that theory
doesn’t work.

No, just an electrolyte so salts which are abundant in the
environment will work just fine in combination with water to
create the galvanic reaction. 

Yeah, just an aside, one of the sells for aluminium was that it
doesn’t have a galvanic reaction with stainless steel in a neutral
environment. However aluminium and stainless steel occur a “lot” in
maritime applications, where the alloys get chewed up, due to the
corrosive salt water environment.

The point being there isn’t really a neutral environment on Earth.

Regards Charles A.


#13

Discussion in this thread included the statement:

you need an acid to make a galvanic reaction- so that theory
doesn't work. 

Actually galvanic reactions happen all the time under many different
conditions, and the presence of an acid is only one of them.

Other examples of circumstances favorable to galvanic reactions
include the presence of any ionic solution (electrolyte), which
could be acid, basic, or a salt; differing concentrations of the
electrolyte present; differences in oxygen concentration (aeration)
at various locations on the metal surface; or even compositional
differences of the metal alloy at various sites immersed in the
electrolyte. Furthermore, the behavior of the reaction products may
modify the observed effects. Galvanic reaction is sometimes
corrosion, but it could be plating out of a metal or evolution of a
gas. All in all, not necessarily a simple process.

I hope this sheds more light on the subject.

R. Davies


#14

Hi again Leonid,

Turns out I was wrong: the ‘classic’ Smithsonian setting is actually
Cartier. Still white metal (probably platinum, but I can’t find a
reliable source for that), but not done by Winston’s. Also in a frame
of white diamonds.

Regards,
Brian.


#15
really old non-ferris metalwork anneals over time, and is
generally shockingly soft 

Annealing is temperature/time curve. High temperature,short time. Low
temperature, long time. So, yes, metals essentially anneal themselves
over long periods of time. It’s like they just “relax.” I’ve never
seen any hard data about it - I never looked for it either - but it’s
one of those little factoids.


#16

Hello

Isn’t hardness or resistance to abrasion an equally important
desirable mechanical property of gold alloys? Hardness affects polish
which also affects reflectance which also affects colour.

Regards
Kofi


#17
We framed some paintings in gold, some in scratched silver, some in
wood etc. 

There are basic facts which require no proof. Some of them are 2 + 2
= 4; water is wet, and painting are always framed in gold by people
who know what they are doing.

Leonid Surpin
Studioarete.com


#18
What we want are color, reflectivity and resistance to corrosion.
And these only begin to resemble gold when at least half of the
atoms are gold. Properly formulated 18k satisfies the requirement,
anything less does not ! 

I don’t know Leonid. All those fine pieces in museums across this
globe made out of electrum (50%± fine gold) belie your argument.

Many cultures appeared to like the color and the working properties
of less or karat gold.

Sam


#19
Yes. That would be why Winston's mounted the Hope diamond in
platinum. Twice. 

I suggest that you take a good look at Hope diamond mounting to
understand why it was done. Gemstone mounting like everything else
has different levels of sophistication. I do not think that I can
explain all the nuances here.

Leonid Surpin
Studioarete.com


#20

Hi

following on from Leonid’s comment on setting coloured gems in 18 kt
yellow.

When displaying coloured gems set in jewellery, white/ivory is a
most effective background colour.

Look at the English crown jewels.

Black ‘kills’ the coloured stones.

When I can I use displays covered in un-dyed fine silk.

Just an observation
Richard