In addition to the widely reported emulsions and interfacial deposits (cruds) encountered in the first extraction stage of the PUREX process, disturbances may also occur in the alkaline solvent wash. Experiments have shown that visually similar, nonradioactive deposits may be generated in vitro using either irradiated or chemically degraded solvents or diluents. Further experiments investigated the occurrence and composition of these deposits using a variety of techniques including physical measurements and spectroscopic methods, resulting in the identification of potential crud-forming species and proposals for mechanisms of crud formation.