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| The cutting-edge chimes of Notre Dame | The cutting-edge chimes of Notre Dame |
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| Quasimodo may be turning in his grave, but the bells of Notre Dame de Paris once again ring true. To mark the cathedral's 850th anniversary, its administrators decided to restore the bells. Only one old bell had survived: Emmanuel, with the deepest sound, dates from 1686. Its fellows were scrapped during the French Revolution and melted down in 1792 to make cannons. | Quasimodo may be turning in his grave, but the bells of Notre Dame de Paris once again ring true. To mark the cathedral's 850th anniversary, its administrators decided to restore the bells. Only one old bell had survived: Emmanuel, with the deepest sound, dates from 1686. Its fellows were scrapped during the French Revolution and melted down in 1792 to make cannons. |
| To repair this sacrilege, four new bells were installed in 1856. But they were not really in tune with the old one, so in February 2012 they were taken down to make room for nine, more harmonious successors. Tipping the scales at 23 tonnes, they cost just $2.6m. | To repair this sacrilege, four new bells were installed in 1856. But they were not really in tune with the old one, so in February 2012 they were taken down to make room for nine, more harmonious successors. Tipping the scales at 23 tonnes, they cost just $2.6m. |
| A set of eight bells was made by Cornille-Havard, a foundry in a Normandy village, with a suitably metallic name – Villedieu-Les-Poêles (literally God's town, the pans). The foundry was started in 1865, with two coal furnaces still in service and three casting pits. "We aim to combine the best of tradition and modern technology," says Paul Bergamo, who heads the firm. Much as 3,000 years ago the moulds are made using a mixture of clay, goat's hair and horse manure (respectively for bonding and heat resistance). "Ancient Egyptians used this mixture to cast their jewels, statues and arms," Bergamo explains. "The mould can withstand temperatures of up to 1,100C." | A set of eight bells was made by Cornille-Havard, a foundry in a Normandy village, with a suitably metallic name – Villedieu-Les-Poêles (literally God's town, the pans). The foundry was started in 1865, with two coal furnaces still in service and three casting pits. "We aim to combine the best of tradition and modern technology," says Paul Bergamo, who heads the firm. Much as 3,000 years ago the moulds are made using a mixture of clay, goat's hair and horse manure (respectively for bonding and heat resistance). "Ancient Egyptians used this mixture to cast their jewels, statues and arms," Bergamo explains. "The mould can withstand temperatures of up to 1,100C." |
| The founders joined forces with researchers at France's Foundry Industry Technology Centre (CTIF), who started by calculating the physical properties of bell bronze: the temperature at which it melts and solidifies, its latent heat, conductivity, density and viscosity. Consisting of 78% copper and 22% tin, this alloy is hard and extremely resonant. Its characteristics do not only depend on the metal itself, but also the way it is cast. For the past decade metal-workers have been testing ways of casting with an upright mould, the aim being to improve resistance. They have also been experimenting with a gating (feeding) technique, already used in industry but never previously for bells. Copper retracts as it cools, reducing its volume, which may cause porosity, then blistering, which spoils the sound. To prevent this, feeders containing molten bronze are located at various parts of the mould to compensate for shrinkage. Their number and size vary depending on the size of the bell. | The founders joined forces with researchers at France's Foundry Industry Technology Centre (CTIF), who started by calculating the physical properties of bell bronze: the temperature at which it melts and solidifies, its latent heat, conductivity, density and viscosity. Consisting of 78% copper and 22% tin, this alloy is hard and extremely resonant. Its characteristics do not only depend on the metal itself, but also the way it is cast. For the past decade metal-workers have been testing ways of casting with an upright mould, the aim being to improve resistance. They have also been experimenting with a gating (feeding) technique, already used in industry but never previously for bells. Copper retracts as it cools, reducing its volume, which may cause porosity, then blistering, which spoils the sound. To prevent this, feeders containing molten bronze are located at various parts of the mould to compensate for shrinkage. Their number and size vary depending on the size of the bell. |
| Bergamo is delighted with the partnership. "Thanks to their measurements the CTIF researchers validated our methods. They also demonstrated that our casting techniques enhance hardness and density by 50%, so the bell resonates for longer." | Bergamo is delighted with the partnership. "Thanks to their measurements the CTIF researchers validated our methods. They also demonstrated that our casting techniques enhance hardness and density by 50%, so the bell resonates for longer." |
| The sound is produced by the striker, also the main cause of wear and tear, with its repeated blows. Wear depends on the properties of the bell itself and the striker, but also the way it is used: swinging, struck from the inside; or motionless, tapped on the outside by a hammer. Prototypes from Normandy took part in a European-wide study of bell longevity, registering a service life of 1,200 hours, equivalent to 200 years if they only ring for a minute a day. The bells of Notre Dame are bigger and will receive fewer blows per minute, so should last several decades longer. | The sound is produced by the striker, also the main cause of wear and tear, with its repeated blows. Wear depends on the properties of the bell itself and the striker, but also the way it is used: swinging, struck from the inside; or motionless, tapped on the outside by a hammer. Prototypes from Normandy took part in a European-wide study of bell longevity, registering a service life of 1,200 hours, equivalent to 200 years if they only ring for a minute a day. The bells of Notre Dame are bigger and will receive fewer blows per minute, so should last several decades longer. |
| For a harmonious sound, bells must be perfectly in tune. The new Paris chimes were designed to suit the oldest bell. "Acoustic analysis showed that it had a deeper sound than most bells, giving it an unusual but pleasant colour," Bergamo explains. Once it has been cast, the sound can be corrected by removing some of the metal. "You can lower the note, never make it higher," he adds, "but the less you change it the better it will sound." | For a harmonious sound, bells must be perfectly in tune. The new Paris chimes were designed to suit the oldest bell. "Acoustic analysis showed that it had a deeper sound than most bells, giving it an unusual but pleasant colour," Bergamo explains. Once it has been cast, the sound can be corrected by removing some of the metal. "You can lower the note, never make it higher," he adds, "but the less you change it the better it will sound." |
| Notre Dame's new bells rang for the first time on 23 March. We have yet to hear how Quasimodo responded. | Notre Dame's new bells rang for the first time on 23 March. We have yet to hear how Quasimodo responded. |
| • This article appeared in Guardian Weekly, which incorporates material from Le Monde | • This article appeared in Guardian Weekly, which incorporates material from Le Monde |
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