The Differences Between Refractive Index Measurements of the External Surface and Bulk Area of Container Glass
THE MICROSCOPE
2016, Volume 64:2, pp. 51–60
DOI
https://doi.org/10.59082/RQFJ6208
AUTHORS
Joseph Insana and Patrick Buzzini
ABSTRACT
Refractive index (RI) is known to be a highly discriminatory optical property used in forensic comparative examinations of glass evidence. RI is known to vary at different locations on a given glass object. In addition to spatial heterogeneity, variation in RI measurements could be observed between the external surface and the bulk of a glass object. Considering the improvements of modern glass manufacturing processes, this study aimed to compare RI data from the external surfaces of glass containers to those collected from their bulk in order to determine if a significant difference exists. The body areas of eight glass containers were selected for this study. A novel methodology was developed to isolate the external surface layer of glass fragments from their bulk. A total of 560 measurements were carried out using the glass refractive index measurement (GRIM) system. The results show that differences were detected for three out of eight containers. Data produced in this study can be helpful to trace evidence examiners when evaluating potential differences observed during comparative examinations or while attempting to explain the dispersion of RI data as a consequence of a sampling method with respect to container glass.