The discover of glass-ceramics, that is, the controlled crystallization of lass, by S D Stookey was a mixture of serendipitous events involving both chance and exploratory research related to a practical concept. However, a combination of awareness of related literature, good observation skills, deductive reasoning, and a strong curiosity for explanatory work, was crucial for this chance event to bear fruit. As was the present case, a review of this story always stimulates new approaches for understanding of the fundamentals of crystallization and the design of glass-ceramics with improved properties. Two experiments of particular interest are presented in this paper. The first focuses on the change of viscosity of a specimen as a function of crystallisation, while the second addresses the improvement of crack resistance by manipulating thermal history during crystallization. This work reveals that glass-ceramic viscosity, that is, bulk viscosity during crystallization, is influenced by both temperature and phase assemblage. Further, as observed by Stookey over 60 years ago, high viscosity is important in controlling the shape of the final product. Finally, thermal history is shown to have a marked invludnce on the crack resistance of glass-ceramics.
