[Jewelry making - Article 00416] - Re: [Orchid] Purify Platinum

[John Sholl]

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    Ahmed, Platinum is a wonderful and profitable metal to work with. It
    can be melted and used over and over endlessly.  The cause of the
    cracking is contamination of some sort. All bits and pieces of
    platinum that are free of solder and other metal can be remelted. As
    can platinum bench filings produces by a saw or rotary file or any
    steel tool. The trick is to make sure it is very clean. Keep a
    separate pan or a baking sheet  to put under your bench pin during
    de-spruing and rough filing platinum pieces. Keep this material
    separate and clean. Do not let it become contaminated with emery or
    rubber wheel dust or you will have to have it traditionally refined. 

    When you are ready to remelt your platinum scrap, it must be soaked
    in a  heated 10% nitric acid bath for several minutes. This removes
    any steel left behind from the file or saw blades. There may only be
    trace amounts but, it will be enough to ruin the platinum. While it
    is easy to soak the bits and pieces, filings can be a little
    trickier. The filings can be placed in a sheet of platinum that has
    been rolled out paper thin then folded around the metal. Close the
    ends so that the filings will not come out but that the nitric acid
    will still be able to get in and clean the metal. (A friend of mine
    described it as similar to rolling a joint but, I'm not sure what
    that means.) Remove this package from the nitric, rinse it, dry it
    and melt it as one piece. This accomplishes two things. It
    eliminates the need to filter the nitric to get your platinum and it
    allows you to melt the filings without having the stuff blow all
    over the place. 

    Some other things to remember are. Do not mix platinum alloys. .95
    cobalt is not compatible with 10% irid ect. Melt the platinum on a
    crucible made for platinum such as a Wesgo crucible. Use this
    crucible for platinum only and store it in a clean place. I have
    never poured my molten platinum into an ingot mold. Instead I melt
    it in a groove carved into the bottom of the crucible. When rolling
    platinum stock always soak it in a 10% nitric solution before
    annealing. The heat it takes to anneal plat. is enough to cause
    material picked up from the rolling mill to fuse into the platinum.
    Platinum must be annealed. To accomplish this bring the piece to a
    bright cherry glow and hold at this temperature for one minute per
    millimeter of thickness of the stock. 

    Also, pick up the book Praktikum Platinschmieden/ Practical
    Platinumsmith by Ruhle-Diebener-Verlag and any of the literature
    produced by the Platinum Guild International. It will be worth your
    while. 

John Sholl
J.F. Sholl Fine Jewelry
Littleton, CO

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