"What kinds of materials count as primary sources vary significantly by field" (66).
Booth, Wayne C., et al. The Craft of Research. 4th ed., U of Chicago P, 2016
"In fields such as literary studies, the arts, and history, primary sources are original works—diaries, letters, manuscripts, images, films, film scripts, recordings, and musical scores created by writers, artists, composers, and so on. Those sources provide data—the words, images, and sounds that you use as evidence to support your reasons. Data can also be objects: coins, clothing, tools, and other artifacts from the period or belonging to a person you're studying.
"In fields such as economics, psychology, chemistry, and so on, researchers typically collect data through observation and experiment. In others, researchers must gather evidence through interviews. . . . In such fields, evidence consists of the data that researchers collect. The primary sources for those collected data are the publications that first publish them" (25).
Turabian, Kate L. A Manual for Writers of Research Papers, Theses, and Dissertations. 8th ed., U of Chicago P, 2013