Beethoven sketched his musical ideas in pencil, as depicted in this image of his work on the Piano Sonata in E, op. 109, and kept his notes and sketches until he died.
According to the Beethoven-Haus in Bonn, the maestro filled about seventy sketchbooks - consisting of thousands of pages - with his musical ideas:
Beethoven made notes of ideas, drafts and elaborations for almost all his works. He carefully kept his work papers. Several thousand sheets (70 sketchbook as well as single sheets) still exist. After his death, the sketchbook were torn apart by autograph collectors and souvenir hunters so that hardly any book remained complete.
The British Library now has Beethoven’s sketchbook with his ideas for the Pastoral Symphony. After it had been “owned” by others - after its original auction (in 1827), not long after Beethoven’s death - the British Museum purchased it in 1880. (For a history of its provenance, after it left Beethoven’s control, see The Beethoven Sketchbooks: History, Reconstruction, Inventory (by Douglas Porter Johnson, Alan Tyson, Robert Winter), page 166.
This image, of a sketchbook page for the Piano Sonata in E, Opus 109, Second Movement, is online courtesy Beethoven scholar Dr. William Kinderman, University of Illinois at Urbana-Champaign.
Click on the image for a greatly expanded view.
Image of sketchbook page for the Piano Sonata in E, Opus 109, Second Movement, online courtesy Dr. William Kinderman, University of Illinois at Urbana-Champaign.
Quoted passage about Beethoven's sketchbooks, online courtesy Beethoven-Haus, Bonn.