This article considers the creation and activation of certification documents codifying the capture-event and moment of enslavement of Reche-Mapuche people during the Araucanian wars with Spanish settlers in seventeenth-century Chile. Certification documents were normalized by the military bureaucracy and activated by slave owners who subjected and maintained Reche-Mapuche men, women, and children in bondage. These documents were foundational because they could reproduce what purportedly happened in other documentary and oral forms and facilitated the circulation of essentialized truths about the enslavement of individuals and about slavery writ large. In their legal petitions for freedom, Reche-Mapuche slaves had to speak against the grain of these legal instrumenta, which expressed a legally enforceable act or action as well as evidence of that action. Certification documents also had an archival afterlife following enactment of the abolition of Indigenous slavery in 1679.