How Bells Are Made
Bells are made of a bronze, known as bell-metal. In early limes, many bells were made of thin plates of hammered iron, riveted together. The bell called clog-an-ead-hacha Phatraic (the bell of Patrick's will) at Belfast, mentioned in the annals of Ulster as early as AD 552, is quadrangular in shape and of this primitive type, as also are some of the Scottish bells.
The small bells discovered by Layard in the Palace of Nimrod, on the site of the ancient City of Nineveh, are cast from copper and tin, in the proportion of 10:1. During the Middle Ages the proportion of tin was increased to improve the vibrants and is now approximately 4:1. Contrary to popular ideas, silver in bell-metal is injurious to tone. Bells have also been made of antimony, brass, steel, gold, glass, and porcelain. Steel bells have a fair tone but a less sustained vibration, and give a higher note than a bell of traditional size and weight in bell-metal. The casting of bells in England began as a monastic craft, but was later carried on by itinerant founders. The method has undergone some changes.
Originally a mould was made of the inside of the bell, the clay being smoothed by band. This was covered with wax to the shape and thickness of the bell required and suitably inscribed and decorated. The wax bell was then covered with thick clay, and the whole warmed over a charcoal fire to melt out the wax. The mould was then baked until dry and the metal poured into the void left by the wax. This method was improved by the employment of two templets, or moulding boards cut from wood, one of the bell's interior shape and the other of the exterior shape. These boards were fixed to a vertical spindle so as to revolve and first a hollow mould of bricks and clay was struck up to the inside shape and dried with a charcoal fire inside. This core mould was then greased, and a false bell of clay struck up on it with the other board and also dried.
Inscription and decoration were set up on this in wax, and the false bell greased and a heavy cope or outer mould of clay built up on it and dried. The drying melted the wax lettering and then the cope was carefully lifted off, the false bell broken away, and the two moulds dressed and reassembled for casting. This 'false bell' method is now superseded by using a single metal moulding gauge for each bell size, moulding the core from the inner edge of it and the cope from the outer edge, the cope being laid up in an iron moulding case shaped for the purpose.
Inscription and decoration are impressed into the soft clay by hand before drying. Advances have also been made in the tuning of bells particularly in the control of the partial tones of which the principal are:
(1) hum note (the deepest);
(2) fundamental note (an octave above the hum note);
(3) minor third interval above the fundamental;
(4) fifth interval above the fundamental;
(5) the octave above the fundamental.
These at least must be correct to produce a good bell. Tuning is done by turning the bells on a lathe and culling metal from the inside.
Most bells have the following proportions: thickness of the edge between 1/10 and 1/15 of the diameter and height just over 3/4 of the diameter.