Wolfgang Amadeus Mozart's String Duo No. 2 in B-flat major for violin and viola, K. 424, the second of the two Mozart wrote to complete Michael Haydn's set of six for the Archbishop Colloredo, was written in the summer of 1783.[1] It is in three movements:
The last movement is a theme with six variations and a coda. As a whole, this duo blends in better with Haydn's four because the viola is more limited to providing harmony than in K. 423. The set of six was presented as all Haydn's, and Colloredo was unable to "detect in them Mozart's obvious workmanship."[2]
By transposing the viola part an octave down and changing to bass clef, the piece is readily playable on cello. Werner Rainer edited such a transcription for Verlag Doblinger.
The B-flat major Duo is almost always paired with the G major Duo, K. 423. The Hungaroton label has a 2-CD set of the Mozart and Haydn duos with Barnabas Kelemen and Katalin Kokas. The Avie label prefers to put Mozart's duos (played by Phillipe Graffin and Nobuko Imai) on a 2-CD set with other pieces by Mozart, such as the Violin Concerto in G, K. 216, and the Sinfonia Concertante in E-flat major, K. 364.