Bulk nucleation has been studied for glasses within the Y2O3–Al2O3–SiO2system, using a two‐stage nucleation and growth heat treatment. The crystalline phases formed have been identified. Annealing in an inert atmosphere is required in order to prevent surface nucleation from dominating the results. Despite this, the phases observed are in general agreement with those observed in previous studies done in air. The nucleation kinetics of they‐Y2Si2O7phase have been measured and the optimum nucleation temperatures have been identified. The kinetic data have been analyzed using two existing models based on classical nucleation theory. The results of this study have been compared with crystallization results of a previous study of glass of similar composition within sintered silicon nitride samples. A two‐stage heat treatment is suggested as a process that may lead to improved devitrification of grain boundary glass in such