Bells and How They are Made
 
 
 
 The Chinese had bells thousands of years ago, but they  didn’t look much like modern bells. Some of then were forged from sheets  of metal, a bit like giant cow bells.
 Modern bells are are cast in a mould, and made of bell  metal, which is a form of bronze, containing 23% tin and 77% copper.  They have been made this way for hundreds of years. The shape gradually  evolved to its present form, as founders experimented to find out what  made a good sound. Compared with modern bells, mediaeval bells were  longer and thinner.
 
Casting a bell
 The mould is made in two separate parts, one shaped like the inside of the bell and one shaped like the outside. 
 
	
	
	
		
		
		
			
		
		
	
	
The  core is built up around bricks on a base plate. The mixture used to  make the mould contains many traditional materials, typically sand,  loam, straw or horse manure and goat hair. The presence of fibres in the  mould is important. They burn in contact with the molten bell metal,  creating tiny tubes that help air to escape from the mould. The final  shape is controlled by using a ’strickle’ - a wooden board shaped like  the cross section of the bell to be cast. Rotating the strickle around  the mould ensures that it is circular.
   
 
	
	
	
		
		
		
		
	
	
The  cope, or outer mould, is formed with the same material, inside a large  iron bell-shaped container. This strickle is used again to ensure the  correct profile inside the mould.  
   
 
	
	
	
		
		
		
		
	
	
When  the moulds are dry they are clamped together ready for casting. After  the molten metal has been poured in, it is left for several days  (depending on size) to cool down before the mould is broken off. The  bell is cleaned and to top is ground level to provide an accurate  mounting surface.
   
  
Tuning the bell
 A bell vibrates in several different ways at the same  time, creating different 'partial frequencies' that depend on the shape  and thickness of different parts of the bells. They are not directly  related, unlike an organ pipe or a guitar string, which generates  'harmonics' related by precise numerical ratios. The shape of the bell  has evolved so that the main partials are in roughly the right  relationship. Removing small amounts of metal from different parts of  the inside of the bell adjusts the different frequencies. A modern bell  is cast deliberately thick, and then tuned on a vertical boring machine  (a giant lathe). Before this, metal was chipped away with a tuning  hammer, a practice that persisted into the early 20th century, despite  the introduction of tuning machines from the late 18th century. 
 The science of modern bell tuning was only fully  understood in the late 19th century, and is generally named after Canon  Arthur B Simpson who first described it. All UK founders subsequently  adopted 'Simpson tuning', which controls five frequencies. Tuning is a  complex process though, because each location affects more than one of  the frequencies, so despite all the science, it still depends on skill  and judgement. The table below shows the five main partials that are  tuned. 
  
PartialFrequency ratioMusical interval  Hum0.5Octave below Prime1  Tierce1.2Minor third Quint1.5Fifth Nominal2Octave above  See a comparison between 
old and new tuning of All Saints bells .
  
Bell foundries
 Of more than 170 foundries known to have operated over  the centuries in Britain, only 8 were still in business by 1900, and six  of those have since closed. Their dates of closure are: Shaw (Bradford)  1902, Blackbourne (Salisbury) 1903, Warner (London) 1924, Aggett  (Chagford) 1926, Gillet & Johnston (Croydon) 1948, Bowell (Ipswich)  1950. Only two UK bell founders remain: 
John Taylor Bell Founders  in Loughborough and 
Whitechapel Bellfoundry  in London. The 
Wokingham Bellfoundry  operated from around 1350 until 1622.
 
Click here  to see how the number of UK bell founders has grown and shrunk over the last 1000 years.