Do you have a ring stretcher/reducer machine? If you do, you can make
a thin 14K band and then make a sterling band which fits tightly over
it. Then use the reducer dies in your ring stretcher machine to push
your ring into, from both sides, to gently produce as much of a dome
as you need. You're smart to practice with copper or silver to test
your results. I've found I need to make the ring(s) size larger than
I need because the doming with the reducer dies tends to make the
ring smaller (duh).