Leda, Unfortunately, there is no safe way to repair such a ring
without some pretty drastic action. First or all, you must remove the
stone. There is no way to heat sink that large a ring and the heat
will get to the stone no matter what you do.
First, let me assume he stone is bezeled...not pronged. If the
latter, it is a fairly easy job. If the former, you either have to
use a jeweler's saw and cut around the ring just below the bezel line
to remove bezel and stone. Another possibility is to cut into either
the front or rear shoulder of the ring setting and gently pry it apart
enough to remove the stone. I prefer the former.
Repair the cracked shank with hard silver solder. Prepare a piece of
flat bezel stock of a width and thickness that it will provide a good
hold on the stone and solder it to the top of the ring with easy
solder, where you removed the old bezel. Clean it all up, file the
bezel, and reset the stone. If you sawed the shoulder, you will have
to open the bezel, solder a piece of sheet silver the width of the saw
kerf into the shoulder, clean it all up and reset the stone. The
problem with this method is, often the bezel has tempered and will not
reset properly. So, I prefer to attach a new bezel.
All that sounds pretty involved but it really does not take that
long. Explain all this to the client before you do any work on the
ring and that there will be an extra charge to 'rebuild' his ring.
Believe it or not, I actually enjoy doing this work and to end up with
a beautifully restored piece.
Oh, and good luck. Don at The Charles Belle Studio in SOFL where
simple elegance IS fine jewelry!