Rubbing your finger around the rim of the glass is much like taking
a bow to a violin string.
Why are we able to produce a tone when we rub our finger around the lip of a crystal glass?
The atoms in a crystal glass are arranged in a very regular pattern, a structure resembling a honeycomb or a chain-link fence. In contrast, the atoms in normal glass are connected irregularly, more like the veg-etables in vegetable soup. The pattern of the atoms in crystal ensures that the glass vibrates in only one way, with one single frequency.