[Jewelry making - Article 00070] - Re: [Orchid] Platinum rings - which alloy is best?

[Teresa Frye]

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Keo,

    I am compelled to jump into the fray on this one as platinum is my
    main product. 

    First, stay away from 5% Iridium platinum! At Hv 80 this alloy is
    much too soft for a ring. You might lose stones, the ring will become
    out of round, it will heavily dent, the list goes on and on. Although
    jewelers love the way it polishes and sets, the consumer will be
    disappointed unless they don't use their hands. (Platinum Guild also
    strongly cautions against use of this alloy for rings.) As a caster,
    I will not supply anything but pendants and earrings from this alloy.
    The same would be true for a Pt950 alloyed with palladium. Way too
    soft with a Vickers of about 68, I believe. An alternative would be a
    10% Iridium Pt, with a decent hardness at Hv 110. 

    My favorite is the 5% Ruthenium platinum. The hardness is Hv 135 and
    Ruthenium is a good choice as a platinum group metal. The working
    characteristics are very similar to a 10% Iridium platinum. PtRu950
    is the alloy used by Tiffany for many years, so it also has a long
    track record of good performance. 

    The 5% Cobalt Pt mentioned in a previous post is also a reasonable
    choice for the consumer, although casters and bench jewelers have a
    lot of complaints as it oxidizes and is also somewhat magnetic. I
    would select this alloy only if the PtRu is not available. 

    As far as securing your stone, Pt is unbeatable if you use the right
    alloy. Platinum jewelry will not lose metal weight over time as gold
    does. Rather than wear down, platinum instead displaces. You will
    see signs of surface wear, however, a quick trip to your jeweler for
    polishing will make your ring look like new again. 

    Not sure about the claim regarding the Pt 1000. I would contact the
    Pt Guild on this one. And, I strongly agree that Rh plating of Pt is
    a bad idea. Why would anyone want to cover up such a beautiful metal
    with a thin layer that will eventually chip and wear down anyway? 

    Bottom line: don't settle for anything less than Hv 110, and better
    yet go for the 135. 

Teresa Frye
TechForm Advanced Casting Technology
Portland, OR

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