Francis Picabia's "La Source (The Spring)" of 1912 several versions are shown in the catalog epitomizes the effort involved in illustrating imagined forms while not actually representing anything specific at all.

WSJ: The Concrete Challenges of Abstraction | Inventing Abstraction | By Tom L. Freudenheim

But few works, since Francis Picabia's depiction of Marie Laurencin as an imaginary machine, challenge convention as much as the portrait of Sir John Sulston by Marc Quinn, recently unveiled at the National Portrait Gallery.

ECONOMIST: The face of portraiture: Making a splash | The