One of oldest party tricks ever is to make a glass goblet resonate by rubbing a wet finger around its rim. Nobody knows who discovered this acoustic phenomenon, probably it's been known since glass blowing techniques were first developed, some time in the first millenium B.C. in ancient Egypt.
The best way to understand how the principle works is to TRY !!! All you need is a stemmed wine glass, not necessarily crystal or any particular material. Wet your fingertip and rub it around the rim, the friction should make the glass resonate giving a pure ethereal sound.
Sometimes this does not work at all or not very well. The reasons can be many, see if you find why in one of the following points:
1- Fingers are not clean.
Before trying wash your hands with a little soap, preferably not liquid soap or too perfumed, these leave residue, then rinse well. Even if your hands are hygienically clean, skin naturally contains oils that keep it elastic and hydrated. This must be removed to have a good friction.
2- Glass is not clean.
Even if the glass looks clean and like before, is hygienically clean, if it was washed with washing up liquid or in the dish washer, it will have an invisible residual coating that will not allow you to have a good friction. Try rinsing well with a sponge using only tap water.
3- Wrong pressure.
Try applying different pressures with your finger. Maybe you are not pressing enough or too much.
4- Wrong glass.
It's unlikely that a stemmed wine glass will not resonate. If however the stem is too long and thin, or the glass is too thick, it maybe difficult to produce a sound easily. Best to try with a normal size wine or cognac glass. Don't go for the fancy shaped and decorated ones.