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Metallurgy - Copper and Silver reactions


#1

This is one for all the Mettallurgists out there! - Regarding using
copper and sterling silver in the same jewelry piece if it is to be
worn next to the skin.

I took a mokume gane class with the crazy talented Chris Ploof and
he informed us, in no uncertain terms that we should not use copper
and silver mokume for rings as it would cause a battery like
reaction that would cause thecopper to erode away. I have since read
this from several other sources…

Question 1 - how severe is this reaction? Why does it happen? can
someone please give me an explanation, kind of an idiots guide
to…

Question 2. If copper and silver (or any other metal) react so badly
together - what happens to the copper content in sterling silver? or
is this somthing to do with the alloy created?

Thank you very much!
Lucy


#2
how severe is this reaction? Why does it happen? can someone please
give me an explanation, kind of an idiots guide to.... 

When you place any two metals in contact and apply an electrolyte
(sweat, water, from the tap, pool, etc) you set up a battery.
Depending on the metals or alloys atomic structure one will be more
positive (anodic) and one more negative (cathodic). The more
positive one will dissolve just like you were using it in a plating
bath as the anode. It is called galvanic corrosion among other names.
There are charts that show the galvanic series with potential voltage
and ordered form most negative to most positive. You can look at such
a chart and get a rough idea how much voltage will be generated from
a given pair of metals. If you look at the chart you will see that
gold is the most cathodic and then platinum and so on. Anyhow silver
is more cathodic than copper so copper will be the metal that is
dissolved. The effect is worst on rings because of all the water we
get on our hands.

If copper and silver (or any other metal) react so badly together -
what happens to the copper content in sterling silver? or is this
somthing to do with the alloy created? 

Over really long periods of time the copper will be leached out of
the sterling but we are talking about burying something in moist soil
or water for years to really see the effect on sterling.

James Binnion
James Binnion Metal Arts


#3
Question 1 - how severe is this reaction? Why does it happen? can
someone please give me an explanation, kind of an idiots guide
to.... 
Question 2. If copper and silver (or any other metal) react so
badly together - what happens to the copper content in sterling
silver? or is this somthing to do with the alloy created? 

Answer to question 1 should take care of question 2.

In order to answer question plainly, I am going to have to dispense
with some formalities. Please bear it in mind when making
"corrections".

Put together metal and liquid and liquid would contain 2 types ions -
positive and negative. (An ion is an atom where balance between
electrons and protons has been shifted, creating electrically charged
atom )

When 2 metal are present, ions of one would have different
electrical potential than the other. When potential is present, ions
will flow to equalize the difference. Since metal would supply ions
into solution constantly, equalization is not possible until metals
are present, so one metal corrodes the other.

Sterling silver can be looked at as silver corroded with copper. If
we let the above described reaction to continue for very long time,
the result will be somewhat similar to an alloy. ( I am using term
alloy very liberally ).

Leonid Surpin
www.studioarete.com


#4

Lucy

This is one for all the Mettallurgists out there! - Regarding
using copper and sterling silver in the same jewelry piece if it is
to be worn next to the skin. 

NO high copper alloys in rings ever. Fingers tend to turn green or
black and fall off. Sterling is usually OK, only 7.5% copper. It is
not the mix or metals, just the bodies reaction to the copper.

Bracelets and neck pieces are less of a problem, less close contact.
Although losing clients when their head turns green or black and
falls off is not good :slight_smile:

No exceptions, and no barrier potions will change this basic fact of
copper and body contact.

jeffD
Demand Designs
Analog/Digital Modelling & Goldsmithing
http://www.gmavt.net/~jdemand


#5

I am new at this and have made quite a few pieces soldering fairly
large 20mm silver pieces to 20 mm copper pieces. Are these in danger
or is it when the pieces are more closely structurally integrated
like in mokume gane?


#6
When you place any two metals in contact and apply an electrolyte
(sweat, water, from the tap, pool, etc) you set up a battery. 

Two good explanations today. As to the severity of it - the old
elementary school experiment is to put a copper wire and a nickel
wire into half a lemon - you can run a small lightbulb off of it, for
a bit. Shipbuilders and plumbers deal with it on a daily basis - a
ship hull with two different metals exposed to salt water will
corrode away very quickly. Plumbers use special fittings where copper
meets iron, and some use copper nails on pipe hangers, too… It’s a
very real phenomenon. Not too mention that elemental copper is toxic
(bad, not so much deadly) above a not very high level.


#7
I am new at this and have made quite a few pieces soldering fairly
large 20mm silver pieces to 20 mm copper pieces. Are these in
danger or is it when the pieces are more closely structurally
integrated like in mokume gane? 

Yes, it does not matter what form the connection is solder, rivet,
bolted or welded. Any contact by two different metals or alloys sets
up the potential for corrosion. You must also have an electrolyte
present so a neckpiece or pin or earrings are relatively immune to
the reaction as they are very rarely if ever wet by an electrolyte.
But rings and to a lesser degree bracelets are susceptible to the
electrolytic corrosion reaction.

James Binnion
James Binnion Metal Arts


#8

Right. As has been pointed out, when you place any two metals in
contact you can set up an electrolytic action that destroys the
copper A few years ago, I had a veritable flood in my downstairs
bathroom, caused by the fact that a copper water pipe had been
installed so that it rested on an iron pipe leading from the
furnace. As a result of the two metals touching each other, the
copper water pipe developed a hole and water gushed through it.
Fortunately, the damage which was extensive was covered by my home
owners insurance.

Interesting first hand proof of electrolytic action.

Alma Rands


#9
caused by the fact that a copper water pipe had been installed so
that it rested on an iron pipe leading from the furnace. As a
result of the two metals touching each other, the copper water pipe
developed a hole 

Hmm. I suspect simple abrasion to be the cause, not an electrolytic
reaction. Pipes move and vibrate with moving contents and changes in
temperature, so there can be an abrasive action, and iron pipe is
harder than copper.

But electrolytic? That would lead one to expect corrsion on the iron
pipe (the more reactive metal of the two) rather than on the
copper… Normally, to get corrosion of the copper, such as has been
discussed in this thread, the other metal needs to be less reactive,
such as silver or gold, for the copper to corrode.

Peter Rowe


#10

Thank you for all the great responses. They were really helpful. I
will keep my mokume gane practice to non-ring items only :slight_smile:


#11

It might be possible to have an acceptable mokume gane ring if the
mokume gane is inlaid in a channel. A channel would provide maximum
separation between skin and mokume gane.

Mike DeBurgh, GJG
Alliance, OH


#12
It might be possible to have an acceptable mokume gane ring if the
mokume gane is inlaid in a channel. A channel would provide
maximum separation between skin and mokume gane. 

It makes no positive difference at all. The problem is not the skin
contact. It is the electrolyte (water, sweat, etc) in contact with
the mixed metals. So a channel or liner will have no positive effect,
in fact it could make it worse if you were to say use a gold liner or
channel as the channel would add an additional metal which is more
cathodic than the copper or silver and make the corrosion happen
faster.

James Binnion
James Binnion Metal Arts


#13
It might be possible to have an acceptable mokume gane ring if the
mokume gane is inlaid in a channel. A channel would provide maximum
separation between skin and mokume gane. 

Nah, I do not believe that is the answer. Just too much moisture,
sweat, soapy water to even consider that as an approach. Use karat
golds, silver alloys, platinum, palladium… The short cuts will
ultimately fail.

Bill