Classical Opera’s well-attended concert at the Wigmore Hall was intriguingly titled “Mozart’s Castrati”. It is well known that Handel wrote many of his famous opera roles for castrati such as Senesino, but perhaps not that much is known about the castrato roles in Mozart’s operas or the castrato singers he composed for – probably because he did not cast castrati in any of his popular da Ponte operas or in Zauberflöte.

In fact, Mozart wrote for castrati in seven of his operas including Il re pastore, La finta giardiniera, Mitridate, Idomeneo and La clemenza di Tito, and one aria from each of these operas were presented in this concert, along with his joyful motet Exsultate, Jubilate composed for the celebrated castrato Rauzzini. There were also arias from Mozart’s near-contemporaries Thomas Arne and J.C. Bach.

One thing we will never know about the castrato is the timbre of their voice, so it was justifiable that the artistic director Ian Page chose two female singers (rather than countertenors) in this concert to sing this repertoire. Also, Mozart wrote for both soprano castrati and alto castrati, and some of the repertoire would lie too high for modern countertenors anyway. The two singers who delivered this repertoire with colour and aplomb were soprano Sarah Fox, a regular performer with Classical Opera, and mezzo-soprano Renata Pokupić, here making her debut with the group. They took it in turns to sing, and the programme was a nice mix of virtuosic arias and more lyrical and contemplative arias.

In the first half, Sarah Fox got to sing the more attractive arias. “Se il rigor d’ingrata sorte” from Mitridate, re di Ponto composed by the 14 year-old Mozart, is a dramatic aria sung by Sifare before going to battle, and Sarah Fox captured the sense of urgency of the music as well as showing technical agility. She also got to sing Exsultate, Jubilate which was elegantly delivered. At times I felt that her vibrato was a little too rich for this sacred work, but this is more a matter of personal taste. Listening to this highly virtuosic piece, especially the famous Alleluja section, we could appreciate what a skilled singer Rauzzini must have been. Also he must have had a very wide vocal range, for whereas Exsultate demands a high vocal range, the preceding aria from Lucio Silla, also composed for Rauzzini, has a much lower range and was sung by the mezzo Pokupić.

The highlight of the second half was Idamante’s recitative and aria from Idomeneo, dramatically and movingly sung by Pokupić. She really entered the character of the young Idamante and expressed his confusion and grief in the aria with genuine feeling and it was as if we were transported to the operatic stage. The last piece of the programme, Sesto’s aria from La clemenza di Tito was also sung by Pokupic. This is a late Mozart work which features richer orchestration, hence it was a slight pity that the orchestra was not always quite together. In general, the orchestra accompanied the singers sensitively under Ian Page's safe hands, but sometimes I missed a slightly more stylish approach to Mozart.

Overall, the programme was well researched featuring different types of castrato arias from Mozart’s operas, but rather than having aria after aria sung by Fox and Pokupic taking turns, they could have brought some more variety by programming some duets that involved a castrato. So when the two singers finally came together for the encore to sing the Act I duet from La clemenza di Tito, the audience were more than delighted. Their resonant voices blended beautifully and it was a satisfying end to an illuminating concert.