[Jewelry making - Article 00067] - Re: [Orchid] Frustrated with final designs

[Peter W . Rowe]

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>        That's what I meant. In a perfect cut all light entering the
>     stone through both the table and pavilion should be reflected and
>     refracted back through the table. 

    Except that's not what happens, Tony.  Most of the light entering
    the pavilion of an ideal cut diamond (and most others) reflects off
    the inner surface of the table, and instead of exiting, bounces back
    toward the opposing side of the pavilion, where it exits.  The visual
    proof of this is simple.  If you hold a diamond over, say, printed
    material, you cannot read the text through the stone. If light
    entering the pavilion exited out through the table, then the image
    of what is under the stone would appear to someone viewing the stone
    from the table direction.  It isn't.  however, viwing a diamond from
    the side, where most of the light enters the pavilion, lets you
    pretty much look through the stone. Looking straight into the
    pavilion facets, you can easily see things reflected in the table,
    indicating that light entering the back which hits the table,
    reflects, and does not refract out.  Try it.  Now, the optics of
    diamond are optimized for light return from the table up position. 
    It happens that this doesn't return much light that enters the
    pavilion.  But that's not absolute. SOME of the light that enters the
    pavilion, especially that which doesn't just hit the table, but which
    may enter at odd angles and end up hitting crown facets, may end up
    bouncing around the stone several times, eventually exiting the
    crown.  Diamonds are just not very good at doing that.  Some, yes. 
    Enough so the color of the metal, or whatever, that's behind the
    diamond does have some effect on the percieved color of the stone. 
    But it's not a large effect. Mostly, it's light exiting the crown at
    oblique angles, as when the stone is tipped appreciably away from
    straight toward the viewer. 

    Colored stones with lower refractive indices may allow more light
    from the back to exit the front.  When that happens, one of the
    visual clues is a window, and the "read through" effect.  In those
    stones, what's behind the stone makes a big difference in the
    appearance of the stone. 

Peter Rowe

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