Chopin: Étude in A Minor ("Chromatique"), Op. 10, No. 2
This étude is an exercise in developing the independence of the weaker fingers of the right hand by playing rapid chromatic scale figures with the third, fourth, and fifth fingers of the right hand. Meanwhile, the first two fingers of the right and the left hand play an accompaniment of short chords and single notes. Chopin indicated the fingering himself note by note for almost 800 notes. Chopin demanded that the chromatic scale be played sempre legato, a direction mentioned seven times throughout the score. This contrasts with the staccato chords played as accompaniment.
Alfred Cortot said that the first difficulty to overcome is the "crossings of the 3rd, 4th and 5th fingers" and the "strain resulting from the continuous action of the said fingers."
It is a particular physical and psychological challenge to perform this étude in public. Kogosowski reports that even "the imposingly powerful Sviatoslav Richter, who possessed the most awesome technical equipment of any pianist in the world, would quake before this tiny piece. When performing the twelve Etudes Op. 10 as a set, he’d hesitate and sometimes skip over the quiet but treacherous second Etude. And Richter was certainly not the only pianist to feel this way about this little Etude."