 His early collection was focused mainly on Italian Renaissance paintings from Siena and Umbria, inspired by Princeton professor Allan Marquand.Later, particularly after World War I, Platt shifted his focus to drawings and collecting from outside of Italy.During this period, he collected work from Guercino, Luca Cambiasi, Théophile Steinlen, Alphonse Legros, John Flaxman, George Romney, and Amedeo Modigliani.