I had no traction with this at all until, upon the suggestion of a
colleague (Sam Sampere) at Syracuse University, I tried beakers
instead of a wine glass. Those work quite nicely. Each one is a
little different, though. It helps to scan beforehand looking for the
resonance with either a mike or resting a pencil on top.
Sometimes it's still a little work. I keep several beakers on hand
so I can try another if the first doesn't go.