[Jewelry making - Article 01150] - [Orchid] Finial casting question

[Karla Maxwell]

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    Hello Orchid Friends - About a month ago I asked a question
    regarding materials used for Japanese cloisonnE9 vases. I had been
    asked to create missing lids for two of them. At that time I
    received many good Orchid suggestions that sent me in the right
    direction for my answer. [Centuries ago Chinese vases were enameled
    on bronze or brass but they later switched to copper. When the
    Japanese began enameling vases, copper was firmly established as the
    base metal in the finer pieces.]. Now that the project has become a
    reality I find myself in need of additional information. 

    The little lids that I will be producing each have a small finial
    shaped like a tiny chrysanthemum bud approximately .32" x .37". I
    was given a finial from another vase to use for reproduction
    purposes. I have 2 issues: 

    The finial / vase is over 100 years old. This small item has a
    patina that I can't mess with. It also has definite gunk that I know
    must be carefully removed or I will be reproducing that antique gunk
    in the new finials. This is the lessor of my problems. 

    Secondly, I've been told by the castor that if he uses vulcanized
    rubber for the mold, we will get shrinkage and the surface of the
    original will probably have a color change. I can't live with that!! 

    The original seems to be made of a pinkish bronze or copper. There
    are small areas visible where gold plating has been worn away. 

    Below are snips from the archives mentioning materials that may do
    the job [small amount of shrinkage] but my main question of a
    possible color change to the original metal doesn't come up. 

    HELP! What is the answer? 

    I have taken some liberties in editing: 

    From   Bill Mull, Zero-D Products, Inc:  You can accelerate a
    platinum cure silicone's set time dramatically with the application
    of heat. You will give up a little in shrink, but you can cure a
    mold in 1/2 hour or less.. The shrink of platinum cure RTV is under
    1/10 of 1% if cured at room temperature, 

    From:  Dana Carlson, The Alchemist Casting Shop:  Vulcanized
    silicone. Shrinks less than vulcanized rubber, for the most part...
    It doesn't oxidize silver masters.. You need a vulcanizer that will
    get hot enough. You need a metal master. 

    From: Daniel Grandi, Racecar Jewelry Co. Inc: [speaking of Akron
    Silicone RTV]  Silicone RTV is initially costly, but it makes a
    permanent mold (unlike the less costly urethane RTV which tends to
    revert over time, especially in moist regions). RTV molds do have
    some small percentage of shrinkage.... 

    From: Thomas Blair.Quick-Sil is a 2 part RTV 2 lb. with 0%
    shrinkage, item # 160-135 from Swest, 15 min cure time, and works
    well, but don't think anything reproduces detail like Exaflex. You
    can use QS in a mold frame and cut out like vulcanized rubber.
    Thomas Blair 

    From: Todd. Hawkinson...  [Speaking of the Silastic group of
    silicone mold materials]  All have virtually no shrinkage and are
    contaminated by sulfur and gum rubber contact. Shelf life of about
    two to three years.. L RTV - Light green silicone. The best jewelry
    mold making silicone available. Pours, cuts and injects great. My
    silicone standard to compare all other silicones to. I guarantee if
    anyone tries this silicone they won't go back to anything else. 

    From: John Henkel, J.A.Henkel Co.,  use the Liqui-Cast RTV on one of
    a kind carved waxes and pieces that need a mold with 0% shrinkage
    (keep in mind that some injection waxes can cause more shrinkage
    than some mold rubbers). 

    Michael Knight at CASTALDO.....We have a excellent RTV rubber
    [CASTALDOAE LiquaCast 0% Shrinkage RTV Liquid Jewelry Molding
    rubber] similar to Silastic but not thick as tar, not frightfully
    expensive, not easily torn and lacking in strength, not hard to mix,
    hard to de-bubblize and not hard to use. And not a silicone - a
    newer technology. 

    And from a different post from Michael speaking of Quick
    Sil.....Firstly, the rubber is not a liquid and thus is not wet and
    will not wet. It is a clay-like putty.  Secondly it sticks to
    nothing, not even itself.


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