This research is concerned with linear and non-linear optical properties of colloidal microparticles. The microparticles are prepared by methods such as condensation, oxidation-reduction reaction, and electrical dispersion. The nonlinear optical properties are investigated using the frequency-doubled output of a Nd:YAG laser at 532 nm for degenerate four-wave mixing. A determination of the third-order susceptibility is made from the intensity of the optical phase conjugate signal generated in the four-wave mixing. The nonlinear optical property of the microparticles is determined as the function of cluster size and composition. These studies are of interest because they: a) will allow a direct test of the predictions of theory, b) will enhance the current understanding of the quantum size effects, c) have possible application in new optical switches, optical gates, etc. and d) will enhance quality of education at a minority undergraduate institution.