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.