Glass failure analysis requires looking at failed bottles and determining the cause of failure. The failure analysis procedure includes carefully examining the crack pattern and the failure origin. It also helps to have failures with known causes to confirm the conclusions. In this case, bottles were purposely broken using hydraulic pressure. Their performance was documented for future use. Numerous bottles were tested, and all showed similar failure characteristics. All bottle failures were caused by “hoop stress”; thus they started as a straight crack parallel to the axis of the bottle and then branched out. Microscopically, all the over pressure glass bottle failures originated as a slow growing crack and formed a distinct fracture mirror surrounded by mist hackle. Upper left is a photograph of a representative overpressure failure. This particular failure originated on the body of the bottle. Others originated on the heel, but all had the same characteristics. Upper right is a 40X photomicrograph the origin of the failure. It consists of a slow growth fracture mirror surrounded by mist hackle. The small arrows indicate the crack travel direction. During failure analysis, a glass failure analysis expert can compare the unknown glass failure to this example to aid in determining the cause of the failure.