Happy New Year to you too, Linda.
First, I'm going to assume that you're using a faceted stone for
this bezel setting. This is where the study of gemology comes in
handy. When a gemstone is faceted properly, light will enter the
stone through the crown (the top portion), bounce around inside,
hopefully off the pavilion, and exit back through the crown to the
viewer's eye. This is due to the stone's crown and pavilion angles
being cut in harmony with the stone's critical angle. For this
reason alone, opening or closing the back of the setting will have
no effect on the stone's interaction with light, and therefore, it's
appearance to the eye. From this you'd think that an
open or closed back would have absolutely no effect on the stone's
However, oils and grease from our bodies and the things we handle in
our day-to-day affairs can and will be attracted to the stone,
especially on the pavilion of it. This very different substance
(different from the gemstone, that is), when attracted to the
pavilion, actually changes the critical angle of the stone (makes it
much larger) and will cause a phenomenon known as "unplanned light
leakage". This means that light will enter the crown and, instead of
bouncing around the pavilion and exiting back through through the
crown, it will exit through the pavilion, thereby reducing the
brilliance of the stone. This is why gemstone jewelry loses it's
sparkle when dirty and regains it when cleaned.
Even bezel-set stones will attract dirt, oils and grease to it's
pavilion, no matter how closely the bezel is set to the stone. for
this reason, I recommend that, whenever possible, you leave at least
a small open area in the back of your setting to facilitate cleaning
so that your gems may indeed sparkle forever.
James S. Duncan, G.G.