“The artists of the International Style applied [power of observation and delight in delicate and beautiful things], to their portrayal of the world around them… Formerly it was sufficient training to learn the ancient formulas for representing the main figures of the sacred story and to apply this knowledge in ever-new combinations. Now the artist’s task included a different skill. He had to be able to make studies from nature and to transfer them to pictures. He began to use a sketchbook, and to lay up a store of sketches of rare and beautiful plants and animals… The public which looked at the artist’s works began to judge them by the skill with which nature was portrayed, and by the wealth of attractive details which the artist managed to bring into his pictures.”

Ernst H. Gombrich, “Courtiers and Burghers,” The Story of Art, 15th edition