Papers of the American painter, art critic. Correspondence, 1910-1969; holograph and typescript essays, lectures, and speeches; photographs; and printed material, including articles, exhibition catalogs, and material relating to the National Academy of Design, of which Clark wrote a history.

Correspondence, family, business, and personal (1927-1967); artwork, including photographs and reproductions of Martinelli's United Nations commission; statements on his work; and printed material, including clippings about Martinelli (1928-1968), and exhibition announcements, catalogs, and invitations (1934-1968). Correspondents include Aldo John Casanova, Ed Colker, Martin Craig, Dorothy Dehner, Helmut von Erffa, Giannetto Fieschi, Horace Gregory, Peter Grippe, Edmund Haines, Stanley Hayter, Louis I. Kahn, Leon Kelly, Leon Kroll, Norman Lewis, Sam Maitin, Barbara Brooks Morgan, Marnie Pomeroy, Melville Price, Walter Reinsel, Theodore Roszak, Charles Seide, Helena Simkhovitch, David Smith, and Carl Zigrosser.