[Jewelry making - Article 00023] - Re: [Orchid] Platinum vs. Gold

[James Binnion]

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    There is a little misinformation  or lack of understanding recently
    about platinums hardness vs gold.  Most of this comes from people
    remembering the old die struck jewelry of 1920s -1940s This was very
    hard as it had been severely  cold worked by the die forming process.
    however most modern platinum jewelry is not die struck but is cast or
    fabricated so it is basically in its annealed state.  Here are some
    numbers relating to the hardness of some common platinum and gold
    alloys. The information comes from the Platinum Guild's
    "Manufacturing Process Volume 5" and Mark Grimwade's book
    "Introduction to Precious Metals". It is out of print but if you can
    find a copy it is a great intro to the metallurgy of precious metals. 

    From Grimwade " Hardness is a useful property in that it gives some
    indication of the resistance of a material to damage by wear and
    scratching." 

    The hardness values are listed in the Vickers scale (HV) the larger
    the number the harder it is. 

    Platinum- 5% Iridium  Annealed/ as Cast 110 HV 

    Platinum- Cobalt 4.5%  Annealed/ as Cast 135 HV 

    Platinum- 4.8% Reuthenium  Annealed/ as Cast 130 HV Cold Worked
    220-230 HV 

    18K yellow gold   Annealed/ as Cast 150 HV , Cold Worked 210 HV 

    18k Pd White gold Annealed/ as Cast 90 HV , Cold Worked 216 HV 

    18k Nickle White  gold  Annealed/ as Cast 220 HV , Cold Worked 350 HV 

    You can see by these numbers that if you are trying to sell someone a
    cast ring and scratch resistance is the main selection criteria then
    18K  nickle white gold is a much better buy than platinum. Also 18k
    yellow is harder than most platinum alloys as cast. 

    	There are some new platinum alloys available that are heat treatable
    that are not widely used that have hardness values in the Annealed/
    as Cast 190-210 HV  ,  Heat treated after cold work 420-430 HV  this
    is close to some tool steels in hardness but this is a new material
    and is just starting to be used in jewelry manufacturing. 

    Jim -- http://www.mokume-gane.com jbin AT well.com James Binnion Metal Arts
    4701 San Leandro St #18 Oakland, CA 94601 510-533-5108  

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