It’s hard to underestimate the standing of the Hemony brothers—Pierre and François Hemony—in the carillon world. With the likely help of Jacob Van Eyck, they were the first European bell founders to effectively tune the lower five partials in bells. Before them, an instrument of well-tuned bells was a dream that many strived for but couldn’t quite attain. The Hemony brothers proved that bells could be precisely tuned to play harmonious music. After their deaths, they were known as the Stradivarii of the carillon—how’s that for a reputation?
Before we go further, it’s important to explain the relationship between Jacob Van Eyck and the Hemony brothers.* We have limited evidence that they worked together in the fine art of bell tuning, so we must be careful to present their collaboration as a likelihood, not a certainty. In 1643 the Hemony brothers had set up a foundry in Zutphen, Netherlands, the same city as Jacob Van Eyck. This is probably when their collaboration began, since the Hemonys cast a new Zutphen city carillon with which the city officials were very pleased. (Unfortunately, that carillon was lost to a fire in 1920, so we cannot look at the bells for evidence of their collaboration.) A few years later, the Hemonys proposed to cast a new carillon for neighboring Deventer. The same advisers for the Zutphen carillon were sought for this project, and one of those advisers was none other than Jacob Van Eyck. He wrote that he would spend another hour or two with the Hemony brothers to advise them on their bell casting. This is the only written evidence we have of their collaboration.
So what exactly was this tuning method that he most likely passed along to the Hemony brothers? We know the precise bell overtones that they tuned, and that they shaved off metal from the inside of the bell—but how exactly did they do it? The first big leap in bell casting via the Hemony brothers was the understanding that a well-tuned bell did not arise from good casting alone. Prior to the Hemonys, bell founders did not adjust the tuning once bells were freed from the molds. They were only tuned with chisels to the inside—and crudely at that—if the bells were deemed inferior. In contrast, the Hemonys tuned all of their bells as their standard modus operandi by precisely shaving metal off from the inside.
To do this, the bell was placed on a lathe and turned through the force of five or six men. A chisel was placed at a particular spot inside the bell, and as the bell turned, the metal was shaved off and the frequency of a particular overtone went down. Probably through Van Eyck’s experiments, they knew the best spots on the inside to tune individual overtones. How did they know when the overtone had reached the correct frequency? Sympathetic resonance comes to the rescue! The Hemony brothers had a tuning bar set out with the desired overtone frequency. Then, they covered it in sand. When the bell reached the desired overtone frequency, the sand on the tuning bar would begin to dance owing to the vibrations of the tuning bar (the bell would have been ringing during this time due to the chisel against its bell wall). Once they saw the sand jumping around, they knew it was time to stop turning the bell.
* Information for this post taken from Luc Rombouts, Singing Bronze: A History of Carillon Music (Leuven, Belgium: Leuven University Press, 2014), 88, 90-91.