According to "Encyclopedia Britannica," bell metal is a bronze. Bronze is made by melting copper and tin together. The metal is mostly copper, with just a little tin added in. After the right mixture is made, the molten alloy is poured into a mold and allowed to cool. Bear in mind that many bells are extremely large, such as church bells. These bells can weigh as much as 1,500 pounds. To put this figure into perspective, it is almost the same as the weight of a small car.
The ratio of bronze to tin is about 80 percent copper to 20 percent tin. Bell makers experiment around with the exact ratio, to find just the "right" sound. "Encyclopedia Britannica" states that the tin content should be anywhere from 20 to 25 percent. This five percent variance may not seem like much, but changing the percentage even a little bit affects the tone significantly. Noted percussion author and researcher Thomas Rossing states that adding in lead, no more than 10 percent, increases damping, giving the bell a more muffled tone. Therefore, for a very damped bell, the ratio would be 80 percent copper, 10 percent tin, and 10 percent lead.
Rossing states that having an exact mix is not enough. Porosity, which refers to how much air is trapped inside the metal, is a significant factor in terms of sound quality. Porosity refers to how much air is trapped inside the metal. Rossing states that a porous bell has undue damping, making it sound muddy or overly muffled. Bell makers have to minimise the porosity as much as possible during the casting process.
Other materials have been experimented with, such as cast iron or aluminum. Rossing states that these do not produce a tone as good as bell bronze. The conclusion reached is that bell metal--or bell bronze--is the best metal to use for sound quality.