The answer is contained in your question. You wrote:
When I hang a pendant around my neck, the stones don't catch the
light as well as they do lying flat on my workdesk.
You’re right! They don’t!
The optical properties of a cabochon are very different from those
of a faceted stone. When you bezel set a translucent cab, you
drastically reduce the amount of light which enters through the side
of the stone. That’s why your Almandine appears darker in a setting
than it does on your workbench.
Any tips on designing with the stones so they catch the light
when worn? I don't want to put a hole behind them. I tried that
with amethyst and it made no difference.
One option is to use prongs (as few as possible) instead of a bezel.
(Yes, I know that involves more work! ) A prong setting will
allow light to enter your cab from the side. Side-lighting is an
important consideration when setting translucent or transparent
cabochons; whereas it’s nearly meaningless when setting faceted
stones. If your design requires a bezel setting, try to cover as
little of the stone as possible.
Another good option is to purchase cabs with polished backs.
(Polishing the back of a translucent cab increases the quantity of
light which is reflected up toward the dome - thus making the cab
appear brighter. Cutting a convex surface on the back of a cab will
also improve light return; though it makes the cab considerably more
difficult to set.)
I have quit using amethyst cabochons for this reason. Is it
necessary to always use lighter colored stones?
Color saturation won’t cause the problem you described, unless the
coloring agent in the stone has rendered it nearly opaque.
I hope this is of some use to you, Janie!
Peter B. Steiner
Buffalo, NY, USA