[Jewelry making - Article 00018] - Re: [Orchid] Gemstone "windows"

[coralnut]

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Dan,

    Essentially you are correct.  Each stone has a 'critical angle',
    i.e. an angle below which no main facet on the pavillion should be
    cut.  For example, quartz has a critical angle of 41deg.  There are
    two types of facets on the pavillion of a round brilliant....the 16
    break facets (those nearest the girdle) and 8 mains (those that meet
    at the culet ((point)). If the mains are cut at or below 41 deg, the
    path of light entering from the table (top) of the stone will not be
    reflected in the stone in such a way as to cause brilliance or other
    light giving qualities.  Instead, the stone will appear as a piece of
    flat glass and you will be able to see directly through the
    stone....to the point that you will even be able to read through it. 
    Most faceters leave at least one degree clearance.  Diamonds are
    even more critical and huge debates have raged for years about the
    proper angles to be used in their cutting.  If you really want more
    information on that, go to www.acagemlab.com 

    You are correct in assuming that a stone with no window is the more
    valuable (all other aspects being equal) because it displays better
    light properties and appears brighter. Of course, in colored stones,
    depth of color and other factors are important. For example, dark
    tourmalines are often cut in such a manner as to cause more light to
    pass into and out of the stone simply to enhance the
    color...tourmalines are certainly not known for their brillance
    anyway.  There are also extensive computer programs (cad/cam) that
    aide faceters in designing stones and determining the best angles to
    achieve the best light qualities. As you know, expecially when
    purchasing expensive stones, cut is one of the chief qualities that
    must be evaluated. Though presented in somewhat simple terms, hope
    this helps. 

    Cheers from Don at The Charles Belle Studio in SOFL where the white
    bellied snow birds will soon be arriving and where simple elegance IS
    fine jewelry! dcdietz AT attbi.com 

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