[Jewelry making - Article 00144] - Re: [Orchid] Polishing Platinum

[David L. Huffman]

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Hi Steven;

    Contamination of platinum is a problem in this regard: Platinum,
    especially if it's cast, tends to be slightly porous on the surface
    unless it has been worked to compact the surface, so gold, silver,
    and other alloys in buffs get picked up by this surface. Same
    contamination can happen from files (which are always shedding tiny
    bits of steel), and from abrasives contaminated with other metals.
    Also, platinum, because it is so soft and dense, tends to grab other
    metals, as if it were sticky, so it can pick up steel from rolling
    mills and hammers. Although these are minute quantities, further
    planishing and rolling can drive the into the surface, and further
    hammering and milling add more. Cleaning in nitric acid removes a
    lot of it, especially the iron or steel, which is the most
    problematic because it oxidizes before it melts and alloys with the
    platinum. 

    When you weld platinum or even use the higher temperatures of
    platinum solders, it's well above the melting point of the other
    metals. In fact, many of them start to vaporize at those
    temperatures. This is bound to leave pits in your solder seams or
    welds which can only be removed by cutting out the offending areas.
    Also (and I speak from personal experience), when those metals have
    melted into the weld, (as would lead in a gold solder seam) as you
    get up to the flow temperature of the weld, they vaporize and the
    molten platinum makes a small explosion and sprays tiny, really hot
    bits of molten platinum, usually spitting them right in your face. It
    makes quite a "pop" as these gasifying metals try to escape the melt.
    Scares the heck out of store managers too as it blows away a section
    of the ring shank you've been soldering. 

    I also tend to not bother with separate tools for platinum, since I
    don't do nearly as much work in it than I do in gold. I rely on
    frequent cleaning with ultrasonic and pickling in nitric. And when
    I'm ready to weld or solder it, I take a lot of care to get it clean,
    since it's a costly metal in the first place, but especially when you
    have to give the refiner his share after you've contaminated it. One
    day I'll be more disciplined and do it the right way, but like you,
    I've been getting away with being a tad sloppy. 

David L. Huffman

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