A successful industrial crystallization typically requires the development of a robust process in the laboratory Knowledge of the solubility curve and the stability of the solution in the vicinity of the equilibrium point, as indicated by the metastable zone width, is essential to the successful development, optimization, and scale-up of a crystallization process. Use of the Lasentec Focused Beam Reflectance (FBRM) system, with aqueous potash alum solutions, to determine both the metastable zone width and solubility curve is demonstrated. The measured metastable zone width data are also used to estimate the nucleation kinetics of the system. Lasentec Particle Vision and Measurement (PVM) images are also employed to validate the results. The data collected using the FBPM system compare very well with published literature values for potash alum solubility and metastable zone width in aqueous solutions.