Painting portraits from life is the best way to train the eye to "see".  While photographs reproduce the image they fail to provide the subtlety of light, temperature, edge and value that is only visible with the human eye. These images illustrate this process.  The first is a photograph of the model.  The second image is a photograph of the painting at about two hours into the process.  The third image is a photograph of the completed painting after four hours of painting from life. The model was illuminated by natural cool north light coming from the left as you view the model.  The right side of her face, while mostly in shadow, was receiving some warm ambient light.