Gel structure commonly depends on sample history and preparation protocol, and we find that the structure factor S acquired by small-angle X-ray scattering (SAXS) of ITO nanocrystal gels evolves systematically with the amount of the non-coordinating 0.01 0.1 q ( Å-1 ) salt, tetrabutylammonium hexafluorophosphate (TBAPF 6 ), present during gel formation (Fig. and). The enhancement of the primary peak at wavenumber q ∼ 0.05 Å-1 and progressive deepening of the minimum at lower q are reminiscent of coarsening, suggesting the salt concentration determines the extent of structural evolution approaching arrest. These features are replicated in Brownian dynamics simulations of coarsening of nanoparticles with strong, short-ranged attractions (Fig. and S13. Indeed, the S at higher [TBAPF 6 ] superposes with S for a lower [TBAPF 6 ] gel at longer aging time, supporting a correspondence between the effects of salt concentration and time (Fig. ). However, other structures, like cluster fluids of varying cluster fractal dimension, can have similar S, so S alone is not sufficient to determine the microstructural evolution (Fig. ).