Source: http://www.chinaculture.org/gb/en_chinaway/2004-11/30/content_63668.htm
A bell may be regarded as a tensed membrane that is folded in a cup shape (although they are manufactured by casting, not as folded sheets). It may also be regarded as a pipe that is closed on one side, but as the air is not blown, but moved by the membrane like bell body, it should rather be regarded as a membrane.
Bells are typically made of metals, but also of glass and similar tensed materials, and in more ancient times of clay. The casting of large metal bells is quite an art, and although mastered long ago by the Chinese, much later in Europe. The circumference thickness of wall sections must be similar to create quality overtones.
Bells of all shapes and sizes are found in most cultures that have developed metal smelting techniques. Chinese bronze bells have been found that date back to 3'600 years. Sizes range from smaller than 1cm, used as jewelery, to massive religious bells, such as used in Christian churches. The smaller the bell, the higher frequencies; while larger bells create lower frequencies. It is posisble to create bells for each required pitch in a pitch set ("octave").
The bell is struck by a hammer type of object, called a clapper. It can be struck on the outer wall, or inside. Some clappers are fixed to the interior (such as found in handbells).
Source: http://www.chinaculture.org/gb/en_chinaway/2004-11/30/content_63668.htm