California glass expert witness performed a failure analysis on a pyrex glass baking dish. This dish was made from pyrex borosilicate glass, and the glass failure occured as the dish was being removed from the oven. The failure initiated at an internal glass defect. The defect appears to be a colapsed bubble (seed) in the bottom of the dish. The upper left (Mag 8X) photomicrgraph is an overview of the failure origin. Upper right is a higher power (Mag 40X) magnification of the origin. It appears as if the bubble colapsed during hot forming of the pyrex glass baking dish. Because the surfaces of the bubble did not re-weld, a stress riser was created that caused later failure as a result of thermal stresses created during normal use.