Article: RI Variation Within Container Glass


This quarter’s issue of The Microscope  (V. 64, Second Quarter) features an article co-authored by Microtrace microscopist Joseph Insana and Prof. Patrick Buzzini of Sam Houston State University. In the article, entitled “The Differences Between Refractive Index Measurements of the External Surface and Bulk Area of Container Glass,” the authors demonstrate that in some cases, the refractive index of glass (a prime optical characteristic used for distinguishing one glass from another) is not uniform, but instead shows differences depending upon the sampling area.

The article represents of several years of research efforts that the authors have presented and refined at conferences including Inter/Micro 2015 (Chicago), the 2015 NIJ-RTI International Impression, Pattern, Trace Evidence Symposium (IPTES) (San Antonio), and the 2016 meeting of the American Academy of Forensic Sciences (Las Vegas).


Joseph Insana, B.S. and Patrick Buzzini, Ph.D.
The Microscope 64 (2), pp 51 – 60

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.


To read about other research conducted by Microtrace on the variation observed in container glass, click here.


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