There's something about unfinished paintings I find intriguing and mysterious. Interrupted for a variety of reasons, though usually because of death or dislike, they give a fascinating insight into an artist's technique, but more than that, they almost make a post-modern sub genre of painting in themselves. Most famous painters have a famous unfinished painting, from Cezanne and Ingres to Balthus and Michelangelo (I love his Madonna and Child with Saint John and Angels, above, with two ghost-like unfinished figures behind the Madonna exposing her breast. I equally love his unfinished slave sculptures, struggling to escape the rough marble). Some painters deliberately left some of their canvas blank or unfinished in order to draw attention to a particular part of the image, such a well-painted face, leaving the rest of the picture in a sketch-like state.
Pop artist Mel Ramos actually produced a series of playful nudes called Unfinished Paintings (above), painting the face area of the model in detailed colour and the rest of the scene in sketchy monochrome.
Artist Colin Chillag also explores the idea of unfinished paintings in his series of partially painted photorealistic pictures. The paintings are a chance for viewers to see his technique of working, though for me they're somewhat self-conscious.