The epistemological challenges of the Anthropocene trouble distinctions of solid and fluid. In this contribution, the author proposes, after Gabrielle Hecht, that the nuclearity of the Anthropocene contributes significantly to destabilising these categories. Nuclear materials and ideas of nuclearity force (re)consideration of deep timescales and imperceptible processes, problematising fixed material ontologies. The article engages with nuclear matters and queries the logic of solids and fluids by developing the notion of elemental memory. An attention to elemental memory – an element’s capacity (...) to auto-affect over time – reveals the inadequacy of terms like solid and fluid, and highlights the expressiveness of solid fluid substances. Empirically, the author demonstrates, first, how elemental memory informs the solid-fluid processuality of radioactive glasses, especially trinitite. Second, engaging with the work of artists Mari Keto and Erich Berger, she addresses the slow auto-transformations of radioactive minerals. (shrink)