HOW TO MAKE A BELL
Watch our "How to Make a Bell" video on YouTube (opens in a new window).
Big Ben was the largest bell ever cast at Whitechapel Bell Foundry, and as part of our project, we visited Whitechapel Bell Foundry to learn how a bell is made. It is a fascinating craft; the process has not changed much since 1858 when Big Ben was cast. It takes up to two weeks to make a large bell, and the work is painstaking. Everyone must get his work EXACTLY exact, or else the bell will be ruined.
Part 1: Preparation
To make a bell, you start with a STRICKLE. The STRICKLE is the pattern for the bell. You use the same strickle to make the inner mould and the outer mould.
You also need LOAM. To make LOAM, you need: CLAY, RECYCLED LOAM, SAND, HORSE HAIR and MANURE.
Sift and mix your ingredients (clay, recycled loam, sand, horse hair and manure).
Mix the ingredients well and add water. Bake some of the loam into bricks. You will use the LOAM and LOAM BRICKS to make the inner mould and the outer mould.
Part 2: Make the Mould Case: The Core and the Cope
Using LOAM and LOAM BRICKS, build the inner mould (the CORE). Use the STRICKLE to check the shape of your CORE as it rises up. When you add LOAM to the surface, you fling it to remove the air bubbles. If you don't do this, the CORE will explode when you bake it in the oven.When the CORE is ready, bake it in the oven and add a layer of really smooth LOAM. Then, coat the CORE with graphite. You do this so the bell metal won't stick to the CORE when the bell is cast.
Next, build the outer mould (the COPE). You use a bell-shaped case for your COPE, and you use the exact same STRICKLE. You fling the LOAM inside the case and you check your work with the STRICKLE. Little by little, the LOAM builds up inside the bell-shaped case. When the COPE is ready, you bake it in the oven and add a layer of really smooth LOAM. Add an INSCRIPTION to the COPE and coat it with graphite.
Now it's time to close the mould case! Lower the COPE down over the CORE and clamp them together – TIGHTLY! If you don't clamp them together tightly, the hot liquid metal will leak out of the bottom when it's poured.
Once the MOULD CASE is ready, you need a RUNNER BOX. It's like a funnel for the liquid metal to run through into the MOULD CASE. Make the RUNNER BOX from a steel rectangle and sand; the sand has to be packed REALLY tightly or the liquid metal will leak out.
You're almost ready to cast your bell. Turn the FURNACE on and heat up the proper amount of COPPER and TIN to 1150 degrees Celsius. At 1150 degrees, COPPER and TIN turn to liquid metal. At that temperature, it's almost as hot as lava from a volcano.
Part 3: Cast the Bell
Before you can pour the liquid metal into the MOULD CASE, you need to clean the "SLAG" off the top of the pot. SLAG is the crust which forms on the top of the hot liquid metal – kind of like skin on custard. It's made up of all the impurities in the metal which came out when the copper and tin melted.
When you've cleaned the SLAG off the top, it's time to CAST your bell!
Carefully pour the liquid metal into a really big LADLE. Check and double-check and triple-check the temperature of the metal. (It's going to be so hot, there will be flames leaping out of the liquid!)
When you're happy with the temperature and the mixture, pour the metal into the MOULD CASE. It takes a while for the liquid metal to fill the mould, and it sounds just like your bathtub tap!
When you see a plume of smoke come from the RUNNER BOX, that's a sign that the MOULD CASE is full and the bell casting is finished!
Now, you have to let your bell cool. It took Big Ben TWO WEEKS to cool, but most large bells take about two days. Once the bell is cool, you can break it out of the MOULD CASE. Its edges will be very rough, so you'll need to smooth them.
Part 4: Skirt and Tune the Bell
Smoothing the rough edges of the bell is called SKIRTING. You use a huge LATHE to skirt and tune the bell.
First, you SKIRT the bell. You put it, upside down, on the LATHE, and you make sure it is in the precise position. Smack dab in the centre of the LATHE. You bring the BIT down to the edge of the bell, and as the bell spins slowly around, the BIT shaves off the rough metal from the edge of the bell. It makes a ringing sound -- just like the sound the bell will make!
After that, you TUNE the bell. It's a technical process, and it's very important to take your time. If you make a mistake now, the WHOLE BELL will be ruined! (No pressure, then!)
You use a computer to measure the five tones* the bell makes when you strike it. You have to make sure all of these different tones line up to each other; otherwise the bell will sound strange. When Big Ben was made, they used tuning forks to tune a bell. Today, most bell foundries use a computer.
You strike the bell several times, and listen; the computer takes readings of the tones. You calculate how much of the bell to remove and then you use the LATHE to cut out some of the inside of the bell. Then you check your work. And you repeat the process as required.
* The five notes a bell makes are: the HUM, the PRIME, the OCTAVE, the FIFTH, and the MINOR THIRD.
When the bell is tuned, it's ready to go! And that is how you make a bell!