"From Theodore Rousseau, Diaz learned much of the technique of his trade, much of the secret of light and shade, and of the art of composition. In the matter of the use of the pigment, too, Rousseau gave Diaz much information, for he had made a study of the chemical properties of colour, a thing that had never occurred to Diaz, impetuous, unbridled enthusiast that he was. I have said elsewhere that Diaz at Barbizon, with the serious Rousseau working near him, turned his attention to a more sober interpretation of landscape, wherein he gave greater thought to form, tone, and construction. He studied trees, rocks, and gave greater attention to the relation of skies, distances, and foreground."