The Art of Making Bells
Bell making is an ancient art that has changed little over the centuries. Although bells are made of many materials, such as glass and porcelain, most bells are made of metal, particularly bronze, which is an alloy of copper and tin. The metals are heated to around 2,000 degrees F and then poured into a prepared mold the shape of the desired bell. After cooling—which can take several days for a large bell—the bell is removed from the mold, a clapper is attached, and the bell is rung to see how it sounds. This is the test for the bell founder, for the sound of a bell depends on a complex interaction of many variables, such as the proportion of copper to tin in the metal, the size of the bell, the size and hardness of the clapper, and how carefully the bell is cooled. But the most important factor determining the sound of a bell is the shape or profile of the bell, which is how the bell curves from its crown to its lip.
When a bell is rung, it sounds as though it is a single note, but it is actually a chord or set of notes reflecting the vibrations of the metal at difference places along the side of the bell. For a bell to sound pleasing, these different notes need to be in harmony, which depends on the shape or profile of the bell. If they are not in harmony, some adjustments can be made by removing small amounts of metal from the inside of the bell at strategic places, but, if that does not work or if the bell is too far out of tune, the bell has to be recast. The history of bells is littered with recast bells, including the Liberty Bell and Big Ben.