Microelectrophoresis Is An Important method for measuring surface properties of colloidal materials. In order to obtain reliable measurements, a good reference colloid must be chosen first, and both the behavior of the reference under a variety of measurement conditions and instrumental factors must be established. Polystyrene latex has proven to be a good reference material. Time-dependent, solids-loading, and electrolyte concentration effects are determined below in order to establish reproducible referencing conditions. Using these referencing conditions, surface properties of silicon nitride as a function of aging time and atmosphere are studied.