Glass armonicas belong to the family of autophone rubbed instruments. The glasses start vibrating according to a relaxation principle : when a finger rubs a bowl, it alternately catches and releases. This creates a series of impulses which set the bowls into vibration. The phenomenon is complex, so the master glass-blower must be very gifted to give the instrument its personality. A number of variables can play a part in how the Glass armonica sounds. If you modify the tone, the mode and the harmonic composition of the bowls change. Thus, two bowls playing the same note will have different tones
according to the materials used, their shapes, their thicknesses, their dimensions, and their hidden defects.

The glass used today is made of quartz.