[Jewelry making - Article 00170] - Re: [Orchid] Light entering faceted stones

[Galarneau's]

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>          When the stones were loose and I looked at them through the
>     table there was plenty of nice reflection. If all that reflection
>     comes from light entering the table why does the glue in the
>     setting, which is below the table, 

    Dear Jim And All, You have started to understand one of the most
    complex problems in facetted gemstones.  Let me start to explain
    what happens to light in a facetted gemstone.  By our new standards
    a perfectly cut gemstone is one which returns the most light that
    enters the stone through the crown to the pavilion facets back
    through the crown facets to the viewers eye.  Sounds pretty simple. 
    Making this a very complex subject is the fact that all light that
    enters the top of a gemstone does not enter a perfectly
    perpendicular angle and that most gemstones are not very uniform in
    structure.  This means that when that light is bent inside the
    gemstone (refracted) its angle upon which it strikes the facet is
    often below or well above the angle at which reflection can be
    maximized.  What a mouthful.  Light that does not enter the gemstone
    at a perfect angle is partially reflected and partially escapes out
    the back of the stone.  Complicating all this is the fact that each
    and every gemstone absorbs light.  That is what produces the
    perception your eye views as color.  On one end of the visible
    spectrum of light is the color white on the other end is the color
    black.  When you see white you are seeing almost a total reflection
    of the light beam with very little absorption.   When you see black
    you are seeing almost total absorbed light and very little
    reflection.  The escaped light is the problem.  Escaped light makes
    for less than total reflection. When this happens anything behind
    the facet is struck by the light.  The same process above happens
    again.  Some of that light from the escaped light reenters the stone
    from the back.  Yes, light enters a stone from every angle,
    including the back.  That is why you can often see  the mounting. 
    This new light has been absorbed and reflected by the new object
    changing its wavelength.  Thus your eye has quite a job analyzing
    and presenting to your conscious this blend of wavelengths of light.
     This is called perception and is a quality of anything that uses
    light to visualize. 

    How do you get around this problem with facetted gemstones.  First
    buy gemstones that have a uniform color and the most brilliance.  If
    you do not want the metal to change the color mount the stones in
    white metal.  Mount the stones with the table as close to
    perpendicular to the viewing angle of the viewer as possible.  For
    cabachons I would always mount my stones in a closed back bezel of
    white or silver metal that I had polished inside as brilliant as I
    could polish it.  I would never mount a crystal cabochon in an open
    back mounting.  In Kurt Nassau's books on color he has a very
    complex graph which shows the relationship of blending wavelengths
    of light to the color perceived by the human eye. 

    This is a short discussion and I have left out many of the details. 
    Do not take my word for it.  Read Kurt Nassau's book he is the
    expert I am just a stone cutter. 

Gerry Galarneau
www.galarneausgenms.com

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