[Jewelry making - Article 00009] - Re: [Orchid] Opal setting philosophy

[Don Rogers]

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>      My thinking is that it might be better to polish the inside of
>     the setting to be more reflective and keep the available light in
>     play longer. 

    Dave, the nature of opal, other than contra luse, is that reflected
    light produces color while transmitted light kills the color.  This
    is the reason that a black backing is used on opals, it reduces if
    not eliminates the transmitted light.  Using a polished backing will
    increase the transmitted light to the point that only a very bright
    opal, a 4.5 to 5+ would show color, and even that would be reduced
    because of the transmitted light. 

    In case anyone is not sure what I mean by Transmitted vs Reflected
    light, a window is an example of transmitted light, it is fully
    transparent. A mirror is a good example of reflected light, you
    can't see through it, but rather the light comes from the viewers
    side.  These are extreme examples.  In faceted stones, the desire is
    for transmitted light that is reflected by the pavilion.  The light
    picks up the color of the stone and the greater amount of stone the
    light passes through, the greater amount of color imparted.  If you
    were to treat an opal the same way, the fire would all but
    disappear.  This raises some interesting problems for those of us
    who facet opal.  We need to strike a balance between getting good
    reflected light and still maintain a transmitted light return.  A
    contra luse opal solves this problem, as it's color is from
    transmitted light. 

    If you think an opal would look better with a polished backing, you
    can test it by cutting a hole almost as big as the opal in dark
    paper.  Lay the opal on a mirror, and place the paper over it so the
    opal is showing through the paper.  Now with normal viewing light,
    appraise the color.  Now take the opal and apply black fingernail
    polish to the back of it and appraise the color again.  You will
    almost always find that the blackened back produces the best color. 

    There are ways to blacken the back of opals that are more permanent.
     The black marking pen is a temporary treatment as well as the black
    fingernail polish.  Both are attacked by moisture and movement.  The
    fingernail polish is more permanent than the marking pen.  A coating
    of blackened epoxy it the best.  Another trick is to use black RTV
    silicone and line the bottom of the bezel.  Let it dry before
    setting the stone.  This is tricky as you need to get an almost
    smooth surface as well as getting the depth correct, all without
    spilling over to the outside of the bezel.  It is not a technique I
    would recommend, however I have repaired a couple designer pieces
    that had the opals set in this manor, and it was a very effective
    way of blackening the back. 

    If you use the black epoxy method, you can set the stone while the
    epoxy is wet, but you must be very careful not to make contact
    between the back of the opal and the metal as you will get a spot of
    transmitted light through that distracts from the appearance of the
    stone.  This is a common problem when doing inlay work. 

Don Rogers

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