The study of ignorance, or agnotology, has many similarities with studies of absence. This paper outlines a framework for agnotology which is shaped by interdisciplinary studies of both ignorance and absence, and identifies properties such as chronicity, granularity, scale, intentionality, and ontology in relation to epistemology as useful for studying ignorance. These properties can be used to compare various case studies. While not all problems of ignorance are problems of absent knowledge, those that are can gain by an examination of the literatures on absence and the concept of the privative. The lack of symmetry in explanation and representation are methodological challenges to studying ignorances and absences.