Network topology uniquely determines glass fragility

The fragility of several network-forming glasses is shown to display a single dependence on the average bond density of the topological network---a network that reflects both coarse-graining for oxide polyhedra and topological corrections for larger super-structural units. Unlike previous efforts to confirm this result, which relied on adjustable modeling, the current demonstration---involving dynamic light scattering in ${(\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{3})}_{x}{(\mathrm{NaP}{\mathrm{O}}_{3})}_{100\ensuremath{-}x}$ glass melts---is achieved in the absence of any such modeling biases.