Glass expert analyzed several leaking wine bottles that eventually broke in half. All the bottle failures occured on the heal. Also, during failure analysis, it was discovered that all of the bottle failures were made in one cavity of a multi-cavity bow mold tool. Bottles from the other cavities did not have this problem. These bottles were made from very thick dark glass. It is believed that the failures were initiated as chill cracks. However, more process development work must be done at the factory to correct this manufacturing defect. Two suggestions are to eliminate any drafts in the factory and increase the amount of post mold flame heating on the conveyer. Bottles made from thick glass are more likely the have this glass failure mode.