In my CD book "Jewelry Photography Made Simple", I describe some
different approaches to the "posing" problem.
In the case where there will be little or no post-processing of the
image, one good way is to use an inexpensive glue gun. A small dab
placed on the bottom of the shank will allow the ring to be attached
at almost any angle to a piece of glass or ceramic tile. The glue
will not leave a mark, and when you are done it can be easily
flicked off with a fingernail; it does no damage to the piece.
You need to be careful to use only a small dot of glue and work
quickly before it cools. Too much glue and it will be visible.
Experimentation will reveal a number of other adhesives, but I
prefer the glue.
If the piece is not too heavy, or the angle excessive, sticky wax
works pretty well, but it leaves a greasy mark on many surfaces and
on the piece.
Frei & Borel (julesborel.com) make small attractive ring supports
that do not really detract too much from the image. They are
triangular, less than one-half inch in size and available in black
or white. The triangle lays flat and the ring is held at an angle by
a small pin-shaped spring. Inexpensive, effective and fast...but
they are part of the image.
The third option is to use anything you wish and remove its presence
using Photoshop or some other image manipulation software. With the
newer softwares, it's easy and fun, although if time is of the
essence or you have many images to complete, you may find it time
consuming. Most folks will opt for the cheap glue gun, available at
any hardware or art supply outlet. Have fun!