[Jewelry making - Article 00047] - Re: [Orchid] Annealing Sterling Silver

[Charles R . Denaburg]

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>     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. 

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

    3. 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 information is a
    guideline, only. 

I hope this helps.

Bob Denaburg
Metallurgical Engineer, P.E.
Amatuer Jewelry "player"
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