The art of bell casting is centuries old, but foundries today follow a similar process to bellmakers a thousand years ago. The size and shape of a bell is planned, a pattern is created, further styling and embellishments are designed, a mold is created and set into a sand pit, and then the bell is cast. See more on how a bell is made.
Casting, or the act of pouring molten metal into a mold, is both a very delicate and a very dangerous process. Depending on the alloy and ratio of copper to tin, ingots of bronze are melted to a temperature of around 1800°F (the melting point of bronze). Of course, bell founders want the bronze to stay liquid long enough for it to flow freely into the mold, so the temperatures often reach as high as 2150°F.
That’s a very high temperature indeed. It will take a while for the molten bronze to return to a solid state that’s also cool enough to touch. During this time, gases built-up within the mold are released through specially-designed sprues, or vertical passages that allow the gas to escape. If gases remained within the metal, it could create a porous, brittle structure that’s prone to cracking.
How long does it take for a bronze bell to cool? That depends on the size of the bell. Most school, farmhouse, and steeple bells (those under 500 lbs.) are allowed to cool for at least a day. Large bells can take a week or even two to gradually cool. Rapid cooling can be another reason a bell is susceptible to fracture or crack – just look at what happened to the Brobdingnagian Tsar Bell in Moscow!
Once the bell has completely cooled, it can be removed from the casting pit for cleaning, detailing, tuning, and fitting the clapper. The bell is then ready to install in a bell tower or other location. All that’s left is to let it ring!
Cover image: Bellmakers wearing specialized protective gear pour molten bronze into the bell casting pit.
