The interaction of impurities and additives on zinc electrodeposition in electrowinning cellhouses are well documented, but generally not well understood. Operators attempt to maximize current efficiency by promoting zinc deposition, while simultaneously inhibiting hydrogen evolution. However, the impacts of impurities and additives are often difficult to understand and predict. Thus, plant personnel are left to ponder whether to polarize (add more gelatin) or not to polarize (add less gelatin). This joint paper by an industrial practitioner and academic scholar attempts to describe the interactions between impurities and additives in simple terms and to offer practical advice on how to control cellhouse operations.