Dürer mined theoretical and mathematical sources for his work, but he also relied on empirical study of the world around him. To his friend and Reformation leader Philipp Melanchthon, he wrote, "As I grew older, I realized that it was much better to insist on the genuine forms of nature, for simplicity is the greatest adornment of art." This drawing depicts the artist's brother Endres, a goldsmith who probably executed Dürer's designs for metalwork. Using charcoal alone, Dürer achieved a range of textures—from the dense pile of the fur collar to the wisps of curly hair. With his prominent jaw and close-set eyes, Endres bears little resemblance to the idealized clasical proportions. For Dürer, observations taken from nature, in all its variety, had a place in art.