From Wikipedia

Omnibus - Lucien Freud

Painting from life, Freud was apt to spend a great deal of time with one subject, and demanded the model's presence even while working on subsidiary elements. A nude completed in 2007 required sixteen months of work, with the model posing all but four evenings during that time; with each session averaging five hours, the painting took approximately 2,400 hours to complete. A rapport with his models was necessary, and while at work, Freud was characterised as "an outstanding raconteur and mimic". Regarding the difficulty in deciding when a painting is completed, Freud said that "he feels he's finished when he gets the impression he's working on somebody else's painting".