WILLIAMSTOWN, MA.- The United States Postal Service issued a new stamp this week featuring a Gilbert Stuart portrait of George Washington from the Sterling and Francine Clark Art Institute’s collection. The 20-cent “definitive” stamp joins the ranks of other postage stamps carrying iconic images of American symbols and historic figures. The George Washington portrait featured on the stamp is one of more than 100 portraits that Stuart painted of the first president based upon three original paintings. Stuart painted three distinct portraits from life: the 1795 “Vaughan portrait,” showing Washington’s head turned slightly to his left (a part of the National Gallery of Art’s permanent collection); the 1796 “Athenaeum portrait,” an unfinished portrait showing Washington’s head turned slightly to his right (jointly owned by the National Portrait Gallery, Smithsonian Institution, and the