Conversation so far:
What was one of Paul Klee's significant works during his mature career?
Paul Klee's Ad Parnassum (1932) is considered his masterpiece and the best example of his pointillist style.
What is something significant about Paul Klee's Ad Parnassum?
Ad Parnassum is one of Paul Klee's largest, most finely worked paintings.
What are some other works from Paul Klee's mature period, besides Ad Parnassum?
Paul Klee's self-portrait Struck from the List (1933)
What can you tell me about Paul Klee's style from his mature period?
Paul Klee used heavier lines and mainly geometric forms with fewer but larger blocks of color.
Besides heavier lines and geometric forms, what else makes Paul Klee's work from his mature period recognizable?
Paul Klee's varied color palettes, some with bright colors and others somber, perhaps reflected his alternating moods of optimism and pessimism.
Was there anyone Paul Klee was working with or influenced by during his mature period?
Paul Klee was encouraged by a visit from Wassily Kandinsky and Pablo Picasso.
How did Kandinsky and Picasso encourage Paul Klee?
In 1933, Paul Klee began experiencing the symptoms of scleroderma. In the later 1930s, his health recovered somewhat and he was encouraged by a visit from Kandinsky and Picasso.
What were some of the scleroderma symptoms that Paul Klee was experiencing?
The disease made swallowing very difficult.
Was Paul Klee still able to paint during the time when he was sick?
Paul Klee's simpler and larger designs enabled him to keep up his output in his final years.

Question: When did he die?
Self-contained rewrite: When did Paul Klee die?