The mechanism of crystal nucleation in a titania‐magnesia‐alumina‐silica glass has been studied by light scattering. Predominantly isotropic scattering centers become anisotropic during the initial crystallization process. This is interpreted as crystal nucleation within glassy concentrations fluctuation of titania. Titania‐containing glasses nucleate readily because of the tendency of titania to segregate in amorphous regions which are more unstable toward crystallization than the original homogeneous glass. The data can be described by a model of scattering by a center surrounded by a region of polarizability of opposite sign. This model is utilized to obtain measurements of the crystallization rate and average crystal size.