The generation of permanent stresses in glass spheres by rapid colling is described, starting with transient stresses that arise during the tempering process. The utility of tempered glass spheres is briefly considered in the context of the permanent stresses produced. Two possible effects of transient stresses are: the risk of in-process breakage as a result of excessive tension in an already cold surface, and bubble formation in - or other distortion of - spheres as a result of high hydrostatic tension in their interior while that is still hot and fluid. In that connection, the distortion of the edges of tempered glass plates is also briefly considered. The mathematical model of tempering spheres, on which this discussion is based, is outlined in an appendix.
