[Jewelry making - Article 00646] - Re: [Orchid] Metals hardness

[James Binnion]

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>         anyone know where to find the hardness (resistance to
>     indentation) of 18 karat yellow gold compared to brass, sterling
>     silver and bronze? 

    Which alloys? By that I mean that there are dozens of 18k alloys all
    with different hardness and literally hundreds of brass and bronze
    alloys. So you need to be specific as to which alloy you want
    information on.  Information on most copper alloys (brass and
    bronze) can be found on the Copper Development Association website at
    http://properties.copper.org/servlet/
    com.copper.servlet.CDAPropertiesSelectionServlet but you will still
    need to know the alloy name and or number. For gold you are going to
    have a hard time as most vendors have never tested their material
    for hardness and so you will have to rely on very limited information
    published in books like "Introduction to Precious Metals" by Mark
    Grimwade. He lists a 18K yellow with 12.5%copper and 12.5% silver as
    being 150 , 225 and 230 HV (Vickers)  the variation is for annealed
    , work hardened and aged(precipitation hardened) respectively.  The
    problem is determining what alloy you have as this information is
    only  good for that particular alloy. Sterling silver ( the Silver,
    92.5%  copper 7.5% variety) he lists as 56 HV annealed, 140/180 HV
    cold worked  and 110/120HV  aged. 

Jim


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