LUDOX silica is a well known and characterized colloid that has been studied using various particle size analysis techniques including acoustic spectroscopy, laser diffraction, and dynamic light scattering. One such product, LUDOX TM-50, is a 50 wt% suspension of colloidal silica in water. It can be used as a “real world” reference material to test the performance of laser diffraction particle size analyzers. As with many colloids, good dispersion is critical for LUDOX TM to meet specifications. The importance of using a simple salt solution to dilute this material is shown below. LUDOX TM-50 has been tested and incorporated as a particle size reference material for the LA-950.