[Jewelry making - Article 00450] - [Orchid] Annealing and Cold Work

[James Binnion]

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Continue from: "My apprenticeship..."
http://www.ganoksin.com/orchid/archive/200611/msg00318.htm

Hi John and Alan,

>>    So, how does hitting silver with a nylon mallet compare to
>>    striking/reducing/raising with a metal hammer, when it comes the
>>    need to anneal? Thanks! 

>     Jim Binnion is Mr. Science - I mean that sincerely, and he can
>     answer in his inimitable way. On a practical level, you are dealing
>     with the deformation of metal. More deformation=more hardness. It
>     doesn't matter, really, whether it's bending, twisting, or
>     smashing. An exaggeration: if you sit there and pound on a piece of
>     silver with your finger nails all day long, it will not harden,
>     because you're not deforming the metal, even though you are
>     pounding on it. A nylon mallet will harden some - depending how hard
>     you hit with it - it's not the hammer so much as the bending of your
>     bracelets that's doing it, though. 

    Mr Science here :-) John you hit the nail on the head of course. Cold
    work is manipulating the metal by bending, hammering, twisting,
    rolling, drawing etc. When trying to define how much cold work has
    been done forging, rolling or drawing are easy to determine you just
    measure the starting thickness vs the thickness after working and
    you can determine how much stress you put into it. However bending
    and twisting are much harder to figure out as they don't reduce the
    section of the work much relative to the amount of work you put into
    the metal. Alan, in the process of bending your bracelet you are
    compressing the inner surface of the metal and stretching the outer
    surface. This does indeed produce significant cold work and the
    resulting work hardening and they can possibly require annealing
    before you can complete the work. Unfortunately there is no simple
    way to determine when you have put enough work into an object by
    bending to get an optimum crystal restructuring during the anneal.
    So you must rely on your hard won experience of just how far you can
    push the metal before it breaks then anneal just before you reach
    that point. From my experience a bracelet in most silver and gold
    alloys should not need several anneals to bend it round the mandrel.
    What you may be experiencing is the stiffening of the metal as it
    begins to work harden makes it harder to bend and you may need a
    bigger hammer or a different system of leverage to bend the
    material. 

    If you anneal too hot or too often (or both) you will end up with
    metal that has an orange peal surface and is not as strong and
    ductile as properly annealed metal. This will show up in working and
    also in polishing as orange pealed over annealed surfaces don't take
    as good a polish as properly handled ones (correctly annealed and
    left in a hard state before polishing). 

Hope this helps,

Jim

James Binnion
jbin AT mokume-gane.com
James Binnion Metal Arts
http://www.mokume-gane.com
360-756-6550
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