"Mention the word castrato to any male music lover," says Nicholas Clapton, "and he'll go green about the gills, because the idea is a terrible threat to his sexual identity." As a counter-tenor who has twice impersonated Farinelli, the most famous castrato of them all, Clapton is in a position to know. And as curator of an exhibition entitled Handel and the Castrati, which has just opened at the Handel House Museum in London, he's determined to bring these monstres sacrés into focus for the first time as people, rather as a historical freak-show.
Castration was first recorded in the Chinese imperial court in 1765BC, when the genitals were removed totally. In 17th-century Europe, though the penis was left intact, castration of eight-year-old boy singers was still a violent business, with the patient being plunged into a bath of milk to soften the genital area, then drugged by alcohol or opium (which often killed them), or by half-strangulation through pressure on the jugular vein. Among the exhibits at the Handel House Museum are two rusty "castratori" - these being the instruments used to dig the testes out.
One anatomical effect of pre-pubertal castration was to prevent the larynx from growing: the castrato's vocal cords were thus smaller and finer-textured than those of an adult male - more like a female soprano's, in fact. And with this soft and flexible apparatus, the singer could perform exceptional vocal acrobatics. "We can see from his scores," says Clapton, "that the things Farinelli could do were jaw-dropping. I recently worked out that well over a thousand notes a minute were sometimes going past his larynx."
Another effect of there being no testosterone in the male body in adolescence was that the joints between the bones didn't harden, so the bones kept growing. The ribs kept growing, too, so the lungs expanded to fill the chest cavity, and could take in more air. "This all meant," says Clapton, "that a castrato could seem to sing for ever."
In Handel's London, the castrati were treated like pop stars, and they amassed commensurate wealth. As Hogarth recorded in his Rake's Progress, one society lady memorably sighed "One God, one Farinelli", when that singer wove his spell. So powerful was the spell, combining masculine presence with feminine grace, that even his rivals were bewitched: sharing the stage with him, the equally famous Senesino forgot his fictional character and embraced Farinelli in adoration.
The strangest episode in Farinelli's career came when he was invited by Queen Elizabeth Farnese of Spain to sing to her chronically depressed husband Philip V. Accepting the invitation, Farinelli spent the next seven years serenading that gloomy monarch every night.
To complement his exhibition's paintings and instruments of mutilation, Clapton is also singing, to give some idea of what castrato art was all about. He's doing some of their arias, and also the vocal exercises they had to spend hours every day perfecting. "The basic requirements were the same as they are now," he says. "To know how to breathe, to pronounce words clearly, to sing legato, and to produce the messa di voce, which is the hardest thing you ever have to do as a singer." He demonstrates: a slow crescendo followed by a slow diminuendo, without a hint of any change in the vibrato-speed.
But while Farinelli famously bested a trumpeter in range and purity of tone, he was a wooden actor: one critic likened him to a calf roused from its slumber in St James's Park by the dainty foot of a milkmaid.
Some of the greatest music ever composed was for castrati, and despite the hostility of the Orthodox and Spanish churches, in Italy thousands of young hopefuls queued to be cut up every year, as Pope Clement VIII put it, "to the honour of God". It was not the custom's barbarity but the advent of a new breed of macho tenors that ended the castrato craze in the 19th century.
The last castrato - Alessandro Moreschi, known as the Angel of Rome - died in 1922, leaving 17 recordings. Although critics rhapsodise over Moreschi's "masculine weight and silky power", it's unlikely that opera houses will ever resound - as they once did - to the cry, "Long live the knife!"
Handel and the Castrati, Handel House Museum, London W1 (020-7495 1685), to 1 OctoberReuse content