NCJ Number
222207
Journal
Forensic Science International Volume: 174 Issue: 2-3 Dated: January 2008 Pages: 222-228
Date Published
January 2008
Length
7 pages
Annotation
This study examined whether differences between the refractive indexes (RIs) of glass fragments of a car windshield and a windowpane could be better distinguished after the samples were re-annealed, which involved repeating a controlled slow cooling of the glass fragments in a specific range of temperatures after prior heating to a selected temperature.
Abstract
The study found that annealing was useful not only for the classification of glass samples but also in distinguishing between glass samples within the same class. For both types of glass, the mean RI was significantly higher after annealing, and standard deviations in RI were smaller. The distributions of RI for both examined objects appeared abnormal; the deviations from normal were observed at both sides of RI distributions. The difference between mean values of RI after annealing and before annealing for both objects was not significant; thus, it would not be a good parameter for differentiating between two heat-strengthened glass objects. The 181 glass samples examined were from car windows (n=72), windowpanes (n=36), headlamps (n=18), optical glass (n=10), table glass (n=10), bottles (n=10), outer part of bulbs (n=10), inner part of bulbs (n=8), and mirrors (n=7). The RI was determined by the thermoimmersion method, using the GRIM 2 system at approximately 589 nm. 5 tables, 11 figures, and 11 references