Skill in the art of embellishment was a prime requisite for any Baroque or Classical singer. Quoting the treatise by the castrato Pier Francesco Tosi, Sir Charles Mackerras points out that many female singers expected the decorations to be written out for them ‘so they would not have to improvise on the spot but could think about the variations and practise them’.

Mozart gave a model demonstration of this when he elaborated a clutch of arias (including one by JC Bach and two of his own) for Aloysia Weber, the brilliant soprano he had fallen in love with in Mannheim. Especially intriguing is Mozart’s treatment of a dignified but slightly chilly aria from Bach’s opera Adriano in Siria. The first of the two ornamented versions recorded here (Mozart prepared four in total) makes the expression more personal and heartfelt, with the liberal use of sighing appoggiaturas, while the second, in deference to Aloysia’s range and virtuosity, transforms Bach’s stately music into a flamboyant coloratura showpiece. Here and in an aria from Mozart’s Lucio Silla, Diana Montague sings the unadorned original text with her trademark mastery of the Classical style, the tone warm and rounded, the phrasing elegant, the registers smoothly integrated. She is just as impressive in Domenico Corri’s artful embellishment of Cherubino’s ‘Voi che sapete’, where for once the decorator becomes the decorated – and the adolescent page acquires an improbable layer of sophistication. Mozart’s elaborations for Aloysia are adroitly dispatched by sopranos Majella Cullagh and Elizabeth Futral, the former intense and vibrant, the latter bright and ‘pingy’, and surely a match for Aloysia in the diamantine precision of her coloratura.

A born competitor, Mozart delighted in taking a particular idea or piece by another composer as his model and then pointedly improving on it. As Mackerras convincingly demonstrates, the bravura aria from JC Bach’s La clemenza di Scipione – in effect a sinfonia concertante for voice and instruments – was the blueprint for Konstanze’s ‘Martern aller Arten’ in Die Entführung. Futral sings both numbers with spirit and technical aplomb, if without quite the warmth and colour the Entführung aria ideally needs. After this riot of virtuosity, the duet ‘Ah, perdona’ from La clemenza di Tito, tenderly sung by Futral and Montague, makes an envoi of serene beauty.

The Hanover Band play crisply and stylishly under Mackerras’s alert direction (though I wish the clarinets had been less reticent in ‘Non sò d’onde viene’) while, as ever, Opera Rara’s documentation is exemplary, with texts, translations and illuminating notes from Mackerras himself.