Movie: Alberto Alessi tells the story behind Richard Sapper's harmonic whistling kettle in our second exclusive video interview with the president of the Italian design brand.

Sapper's 1982 kettle design for Alessi features two whistles, each tuned to a different note, so that a harmony is produced when water in the kettle boils.

"The idea of Sapper was very clear," Alessi explains. "He told me: 'I will design a kettle for you, but it's not enough for me to just design a beautiful kettle. I want to design a kettle that can be multi-sensorial. Not only to the eyes, but also to the ears.'"

Alessi says they struggled to realise Sapper's idea, until his sister discovered a German craftsman who made tuning pipes for musical instruments, which are called "coristi" in Italian.

"One of Sapper's sisters living in Germany found a craftsman producing coristi in the Black Forest," he explains. "After long negotiations with the artisan I succeeded in convincing him to produce two different coristi. One in E and another in C."

Alessi admits that the whistle on the kettle does not always work perfectly.

"I must confess that this object has some materialistic problems," he says. "The two coristi, they were not conceived for this purpose, so it may happen – depending on the place you live and the kind of water – after some time they may oxidise and will not sing anymore."

He continues: "This has nothing to do with the function of the object, the kettle continues to perfectly boil water. But it has to do with the most important function by far, according to Sapper and to me, which is the aesthetic, the emotional, the poetic function. But in every box we include two additional coristi. They are very easy to replace."

This is one of a series of five movies with Alberto Alessi, in which he discusses some of the Italian brand's most iconic products. Look out for our movie about Alberto Rossi's La Conica stove-top coffee maker tomorrow.

Watch all the movies in the series »