Critical evaluation was transformed into understanding, and criticism became not an act of judgment but of comprehension. - Charles Rosen

I do not think that any composer has ever asked for octave glissandi on the black keys, but there is a recording by Moriz Rosenthal of Chopin's Black-Key Etude in which he plays the short octave passage in both hands glissando: it hurts my hands just to think about it.

The etude is a Romantic idea. It appeared in the early nineteenth century as a new genre: a short piece in which the musical interest is derived almost entirely from a single technical problem. A mechanical difficulty directly produces the music, its charm, and its pathos. Beauty and technique are united, but the creative stimulus is the hand, with its arrangement of muscles and tendons, its idiosyncratic shape.

None of Chopin's contemporaries could rival him for the variety and effectiveness of his treatment of the return.