Photographs are powerful vehicles of ideology. Rather than simply documenting and reflecting a lived, material reality, photos express and retain traces of the belief systems that structure a time and a place. Photographs from American Indian boarding schools document a time and a place, but they also express the shifting ideological landscape of what Gerald McMaster calls "colonial alchemy"—the conversion of children from different sovereign indigenous nations into (U.S.) citizens. This article analyzes photographs from the Thomas Indian School located on the Cattaraugus Reservation in western New York taken between the 1890s and 1950s to illustrate the changing terrain of U.S. racial ideology. The photographs show how the goal of colonial alchemy remained consistent, but the knowledge systems that defined Indianness, citizenship, and the humanitarian mission of American Indian boarding schools changed over time.