How do you know when a painting is finished?

This is a question that I get pretty frequently because of the way that I paint - I tend to play around with negative space, leaving pencil marks and areas of the underpainting exposed. 

There's a story about Kurt Cobain trying to perfect a song in the studio and he couldn't get the feeling right. He commented that it sounded better when he was just laying on his back on the couch. And inevitably, that's exactly how they recorded it. Because mood matters and now that computers can play chess, answer questions, predict our musical preferences, suggest purchases, and take beautiful photographs, the so-called imperfections become the pivotal humanizing element of a piece of art.  

The risk that I run is overworking a painting and it's easy to 'drive past the exit.' There are other artists who fight past this point but there's a layered watercolor element of my work that dies when the surface gets too busy and/or opaque.

Gilbert Stuart's unfinished portrait of George Washington is the single image that has most influenced my historical portraits because of its energy, minimalist composition, and earthy color palette. While there are other painters that have had more of an impact on me (Alice Neel, Richard Diebenkorn, Andy Warhol) this painting is my center line. Stuart started the portrait study but never finished it (he'd go on to use it for many other replicas however). Ironically, it became his most well known image and the most immediately recognizable representation of Washington. There is an interesting juxtaposition of craft and speed, spontaneous intuitive energy and finite precision, to the piece and the incompleteness also creates some interesting symbolism for our country and its first leader. Happy July 4th.