In the final part of our conversation with pianist Orion Weiss, he discusses an upcoming album featuring pieces dealing with grief and loss. Ravel honored friends lost in World War I in “Le Tombeau De Couperin.” Shostakovich reflects on a teacher lost in the wake of the Siege of Leningrad” and Brahms captures his mentor Robert Schumann’s fragile psyche in Brahms’ set of “Variations on a Theme of Schumann.”