Charles E. Burchfield (1893-1967), Conventions for Abstract Thoughts: [Nostalgia]: Mute sorrow, Abstraction of Mind and Untitled (Insanity), 1917; graphite on paper, 9 3/8 x 6 1/8 inches; Charles E. Burchfield Foundation Archives, Gift of the Charles E. Burchfield Foundation, 2006