Glass has a variety of uses including windows, doors, containers, light bulbs, etc. Glass may be collected at burglary, hit and run, and assault crime scenes and sent into the lab for analysis.
There are several types of examinations that can be performed on glass in attempt to determine if questioned glass came from a known source. For example, questioned glass found on a burglary suspect can be compared to glass from a window pane at the scene. The first type of exam, typically performed, is a physical match examination. In this exam the questioned and known glasses are examined to see if they fit together and determine if they were, at one time, whole. If a physical match is not found, further examinations can be done to compare the chemical, physical, and optical properties of the glasses.
Glass can also be examined to determine both the order of breaking and direction of breaking. An example of where these exams could be useful is a shoot-out through the windshield of a police car. An examination of the bullet holes in the windshield can reveal which holes were created from a suspect shooting from outside of the car and those holes that were created by the officer shooting from the inside the car. Also by examining the cracks around the holes, the order in which the holes were made, may be determined.