An actual work of art, whether a painting or a building, is a primary source. A primary source is "first-hand" information, sources as close as possible to the origin of the information or idea under study. Primary sources are contrasted with secondary sources, works that provide analysis, commentary, or criticism on the primary source. In historical studies, primary sources include written works, recordings, or other source of information from people who were participants or direct witnesses to the events in question. Examples of commonly used primary sources include memoirs, personal correspondence, oral histories, and contemporary newspaper accounts.
Books written by the artist, such as a journal/diary/autobiography/letters are examples of primary sources. Newspaper and magazine articles written by someone who attended an opening or a talk by an artist would be primary sources. Books and articles written by friends and associates during the artist's lifetime would also be primary sources.