Ensuring good ignition properties over long periods of time necessitates maintaining a good level of flow porosity in powders of initiator materials and preventing particle coarsening. To simulate flow porosity changes of such powder materials over long periods of time a common strategy is to perform accelerated aging experiments over shorter time spans at elevated temperatures. In this paper, we examine historical accelerated-aging data on powders of pentaerythritol tetranitrate, an important energetic material, and make predictions for long-term aging under ambient conditions. We develop an evaporation-condensation-based model to provide some mechanistic understanding of the coarsening process.