This term refers to performers "blacking up" with burnt cork to play exaggerated versions of African Americans, typically in minstrel shows and early musicals, although white actors in blackface often played African American characters in straight plays as well. The minstrel show, one of the most durable entertainments of the 19th and early 20th centuries, ostensibly began in the 1820s when entertainer T. D. Rice adopted the practice in a performance in Baltimore after supposedly witnessing an elderly black man doing an eccentric dance. The "Jump Jim Crow" routine Rice perfected was widely imitated when minstrel shows, which were essentially variety attractions featuring songs, dances, and comedy, sprang up around the United States.
By the 1840s, Dan Emmett founded the Virginia Minstrels, an early prototype of the tradition continued by E. P. Christy and others. Blackface was dropped for a time in all-white, all-black, and mixed-race troupes, but by the 1880s, audiences who had seen it for generations demanded its return. As the popularity of minstrel troupes declined, blackface transferred into vaudeville and musical comedy, used by many white entertainers, including Al Jolson, Eddie Leonard, Eddie Cantor, Bing Crosby, Judy Garland, and by Ziegfeld Follies star Bert Williams, an African American. The technique of applying blackface is wonderfully shown as a part of Jolson's performance in the 1927 motion picture The Jazz Singer. By the 1930s, most performers had abandoned blackface as an outmoded and demeaning stereotype.
The Historical Dictionary of the American Theater. James Fisher.