Objects and artifacts are potent signs of cultural values, and in popular media they are often used as external signs of racial identity. This dissertation investigates how certain objects and settings come to be identified as characteristic of particular racial groups, and how stereotypes about material culture are then exploited to justify discriminatory political policy. I conduct an analysis of the visual representation of Mexicans and the Irish in U.S. media, beginning in 1840 and continuing to the present era. I identify when and why certain artifacts, like potatoes or sombreros, began to be used as stereotypical signs of each group. In each case, I examine how these metonymies were employed as weapons in contemporary political struggles over land, jobs, and representation. Drawing on the records of Mexican and Irish representation, I develop a theoretical model I term "the material discourses of race” to identify the three ways that objects are turned into signs of racial identity, and to explain why certain objects are repeatedly employed to construct an idealized image of whiteness in U.S. visual culture.