Joanne- There are two issues here that I see.
A: Mystic topaz is just quartz with a very this surface treatment.
Quartz is not an appropriate stone for a wedding ring. It’s waaay to
soft for an every day ring. The “mystic” part will most likely die in
the plating process. The center quartz stone may last just few years
B: There is no really permanent surface treatment for silver or gold
that will withstand daily wedding ring wear.
If you look at our friend Sarah Graham’s lovely work, the black part
is a special alloy of steel that she has cast by Techform. Black
rhodium will NOT do. There are some powder coatings that are harder
and will last longer, but they still are just thin surface treatment
that will wear off eventually with every day wear on a ring.
Etienne Perret is doing some lovely work in ceramic in black as well
as other colors. Worth checking out his work.
Have fun and make lots of jewelry.
Just make sure it lasts.