Resizing a ring with a pearl - here are two methods that I use: 1.
Removing a pearl glued onto a post. Have a pair of heavy tweezers or
tongs handy. Hold the ring in your fingers at the pearl with two or
three layers of tissue paper to insulate your fingers; then heat the
ring shank with a torch letting the heat travel by conduction along
the shank to the setting. As soon as you feel the heat through the
tissue, use the tweezers or tongs to hold the ring and try to work
the pearl off the post with your fingers. There are risks with this
method, if too much heat reaches the pearl it will discolour or
flake, fingers can get hot. It is a balancing act. Get an idea of how
much heat you are putting into the shank and how long it takes that
heat to reach the pearl post. Once the pearl is off the base a
little, more heat can be used. I have done this successfully many
times. 2. Do the soldering using a Mudbath - a bowl filled with sand,
and water to the level of the sand. Sit the ring in the mudbath so
that the pearl is completely under the sand/water and the shank is
exposed. Solder the join in this position. This method requires more
heat in proportion to the wieght of the shank, and the type of metal.
Lots of heat is lost in boiling the water where the shank meets the
'mud'. The worst case is a heavy silver shank - for these I need the
oxy/acetylene torch on full blast, and melting the solder before
melting the exposed shank happens in a very narrow time frame. Thin
9ct shanks can be done with a regular torch, heavy 18ct shanks will
need an oxy flame.
Practise either method before working on an expensive item!
I am sure there are exotic welders or melting devices that will do
the job, but I don't have them. So far the above methods have served
me well, after lots of practise they are no longer scary but always
require care and respect.