What is bronze?
Bells are often cast in bronze, an alloy (combination) of copper and tin. While the proportions have been experimented with for thousands of years, the generally-recognized best composition is 80% copper to 20% tin for a bronze of expansive resonance and appealing sound. This 4:1 ratio, called bell metal, comes together in a crystal lattice arrangement of atoms that creates a uniquely harmonious damping capacity (the bronze’s ability to absorb energy) and sound velocity, which is what makes the toll of a bell (and related instruments like cymbals) ripple across a neighborhood.
Different founders have different bell metal recipes to cast their own high-quality bells. Generally, increasing the amount of tin in the alloy increases the decay time of the bell strike, or the length of time a person on the ground can hear the bell ring. Percentages of tin content can vary from 20% to 26%. It is interesting to note that both copper and tin on their own are relatively soft metals that would deform quite easily on striking. However, when combined in an alloy, a bell with greater strength and elasticity can be created. This is crucial for increasing vibrations (resonance) and reducing cracks when the bell is forcefully struck. Over time, the alloy will slowly develop a rich and protective patina called verdigris that makes the bell more resistant to weathering and harmful oxidation.