Two prominent theories surround the origin of secondary nuclei in batch crystallization experiments. Traditionally, the generation of secondary nuclei has been attributed to attrition breeding, resulting from collisions between crystals, impeller, and vessel geometry. Mechanistically, it is assumed that the collision of crystals leads to the generation of fine particles and nucleation sites. More recently, an alternative mechanism has received considerable attention, namely, cluster breeding secondary nucleation whereby the source of fine particles is attributed to clusters in solution. In the present work, a detailed experimental investigation of particle wall collisions of active pharmaceutical ingredient crystals is conducted. A pressurized test rig was developed whereby crystals in suspension were fired through a nozzle perpendicular to a stainless steel target. Using shadowgraphy, direct imaging particle-plane collisions are captured for crystals between 100–400 μm as they approach a target surface w...