If keyword searching in WestCat or a database, try combining your topic ("Marcel Duchamp") with the type of primary sources you're interested in ("letters").
When searching by subject in I-Share, try searching for "Art - 20th Century - Sources" to find books that contain primary sources. (For late 19th century artists, replace 20th century with 19th century.)
One primary source series available at WIU is the Documents of 20th Century Art series. These contain letters, interviews, and essays from many prominent artists and movements in the early 20th century. More books in the series are available in I-Share.
Primary sources are first-hand accounts of events or persons. These sources were present during an experience or time period and offer an inside view of a particular event. In art history, primary sources might include:
Some sources can be primary or secondary depending on how you approach them.
Secondary sources are sources at least one step removed from the events or people they describe. They are often based on analysis of primary sources, and may include quotes or images from primary sources. Examples of secondary sources in art history might include:
Some sources can be primary or secondary depending on how you approach them.