I’m investigating duets in minstrelsy, vaudeville, and the integrated musical in order to understand both the backdrop and the background for vocal duos in the rock era. I came across a wonderful site today. The Boston Athenaeum has a collection of playbills and programs from theaters in Boston during the latter portion of the nineteenth century. They have created an online database in which you can search by theater, actor, play title, and/or date. As I understand it, the database reflects their playbill holdings. In conjunction with the database and collection, they also have brief histories of each of the theaters for which they have playbills. They also have links to some local (Boston) collections, as well as others.
Clearly a trip into town is on the horizon for me.