He might have made his problem easier by throwing a strong light upon the figure from one side. This would have made some parts of the dress shine out with the brightness of very high lights, and would have caused the figure to cast a shadow on the wall. This would have produced a harmony of contrasts; a bold contrast of color values, easier to paint. But Whistler was intent on something very subtle--a harmony of similarities. So he placed the figure in a dull light, that was evenly distributed over the rug, the figure, and the wall, with the result that the distinctions between the color values were very slight, very subtle. This means that it was difficult to make the different masses of white distinct from one another. The artist, you see, had to make it appear that the girl’s white figure was nearer to us than the white wall; to make us feel that, while the wall is flat, the figure has roundness and bulk; and that, while the wall is an upright surface, the rug represents a horizontal one. Yes it was indeed a very difficult problem, because the only possible way of solving it was to render the very slight differences in the quantity of light, reflected from each and every part of the white surfaces, according to the angle at which the light reached any part, and the distance each part was from the eye of the artist. And no doubt the keen mind of Whistler was interested in the subtlety of the problem. But this was not all. His feeling as an artist was equally subtle. It delighted in the subtleties of color values.