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Annealing Sterling Silver


#1

Orchidians,

While hunting on the web today I came across a site
explaining techniques for Jewelers. I found one statement which has
me confused. The site states that Sterling Silver is comprised of
Silver (92.5%), Copper (7%) and Tin and Antimony (0.5%). The author
goes on to state that Sterling can only be annealed about 5 times,
after which it loses the Tin and Antimony and cannot be re- annealed.
Is this in fact true? I have always understood that Sterling Silver
is normally just Silver (92.5%) and Copper or Argentium (7.5 %). I
alloy my own sterling and this is what I use. Can anybody shed some
light on this ?

tks
John Bowling


#2

If silver can only be annealed 5 times I must be in an alternative
universe. But heck, if it’s on the internet it must be true.

jo


#3

John,

I’m not sure the source of this but it looks dated in
the sense that Copper was and sometimes still is alloyed up to 5%,
but usually less than 2.5%, with Tin and Antimony to improve the
wire drawing ability and finish of copper wire when less pure copper
is used. Copper wire was often the source of Copper in Sterling up
through the seventies.

I think the suggestion of annealing five times would refer to a lose
in the finish of the sterling as impurities would be absorbed in the
annealing process,this being increased because the reaction of the
flux with Antimony would lower the protection of the flux. I think
Jim Binnion could add a lot to this. Also, I remember foreign
sources of Sterling such as Mexico were much more common in the
seventies and early eighties.

Modern Sterling is made with pure elements in the US and I think you
will get better results. Annealing many multiple times however does
have problems and requires a great deal of care from the very first
annealing. Oxygen, Hydrogen and Sulfur canl be absorbed and
eventually cause some greying and then cracking. I haven’t done such
a big job as say annealing twenty times recently but in the past when
I have, I used Nitric Acid as my primary pickle as I didn’t have
success with the available commercial pickles at that time. Again
there is lots of good advise available from Orchid.

Dan


#4

I have no idea what the tin and antimony does to the silver other
than lower the melting point, but when it is burned out the remaining
93% silver/copper alloy will anneal just the same as stirling silver!

Alastair


#5

John,

The Silver, Copper, Tin formula is not that unusual. That said I am
unclear about the chemical effects of tin and antimony regarding
annealing. Some of the alloy materials will be depleted over
repeated annealing and working however this largely occurs on the
surface of the object. If you are raising sheet or otherwise
hammering the sterling you will eventually depletion guild the
surface with pure silver to a depth of a few mils. So I feel it is
unlikely that the info you found is true. What will wreck sterling’s
ability to be reannealed is over heating and/or over working. I am
VERY careful with heating the sterling piece. I don’t have a temp
controlled oven for the purpose so I torch heat in very low light so
I can stop at the “right” color. I have been able to reanneal pieces
many, many times. If the website info were true, you could never
raise a sterling goblet or bowl.

Regards,
Bob Claborne


#6
Why is my silver turning cloudy after annealing at 600C when I
anneal in Nitrogen? 

I don’t know if anyone has answered this question or not. However,
there may be several reasons and forgive me if I make assumptions
that are not true, I am just trying to cover most of the problems
encountered:

1: The annealing furnace hearth or chamber may not have been purged
of all the air or moisture.

  1. The Nitrogen used could be contaminated with air and moisture.

  2. Of course, the cool down rate in the normal atmosphere can create
    surface discoloration, as well.

As far as the “dull” anneal problem, the chamber also must be
totally sealed or the “inert” atmospaher gases must be pure and
exhibit a positive chamber pressure where oxygen and/or moisture
cannot get to it. Cool down has to be in the in the inert
atmosphere.

These are some of the most frequent problems I personally have seen
and/or encountered.

Also, the American Society of Metals, Metals Handbook, 8th Edition,
Vol. 2, HEAT TREATING CLEANING AND FINISHING, page 306, depicts the
annealing curves of Precious Metals including Commercial Fine Silver
and Sterling Silver.

The tell tale story on the Commercial Fine Silver is the Percent
Elongation curve where elongation is meaured and plotted against
Annealing Temperature. This curve shows where the Fine silver
increases % elongation from approximately 10% at 400 F (NOT “C”) to
approximately 50% Elongation at 600 F. The curve appears almost
vertical between those temperatuires. This major change in
elongation after exposure to 600 F strongly suggest, after exposure
for a period of time (you have to dertermine that length of time
experimentally for your application), you can obtain nearly full
anneal. Apparently, you do not have to get into the RED heat range
for annealing silver.

The same is true for the Sterling, except the rapid change in %
elongation is experienced between 500 F and 700 F.

I, personally, use both flame and furnace annealing practices and
follow the “pickling advice” unless I am doing quantity, which very
seldom. Oh! I pickle straight from the furnace to the pickle (while
the piece is HOT).

I hope this helps. The experimental approach for your specific
application certainly is recommended and the above is a
guideline, only.

I hope this helps.

Bob Denaburg
Metallurgical Engineer, P.E.
Amatuer Jewelry “player”