Sculpted and textured in ZBrush
Painted the color map in Substance Painter
Rendered in Maya with Arnold

Schubert wasn’t famous during his lifetime and probably couldn’t afford a highly skilled artist to paint his portrait, most of the portraits of him were done decades after his death when his music finally started to make it to the mainstream. All I could find as a reference was just one photo of a cast impression of his life/death mask, unfortunately the original mask is lost or destroyed in the market.