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An Interlaboratory Study Evaluating the Interpretation of Forensic Glass Evidence Using Refractive Index Measurements and Elemental Composition



Ruthmara Corzo, Tricia Hoffman, Troy Ernst, Tatiana Trejos, Ted Berman, Sally Coulson, Peter Weis, Aleksandra Stryjnik, Hendrick Dorn, Edward Chip Pollock, Michael Scott Workman, Patrick Jones, Brendan Nytes, Thomas Scholz, Huifang Xie, Katherine Igowsky, Randall Nelson, Kris Gates, Jhanis Gonzalez, Lisa-Mareen Voss, Jose Almirall


Seventeen laboratories participated in three interlaboratory exercises to assess the performance of refractive index, micro X-ray Fluorescence Spectroscopy (µXRF), and Laser Induced Breakdown Spectroscopy (LIBS) data for the forensic comparison of glass samples. Glass samples from automotive windshields were distributed to the participating labs as unknowns and participants were asked to compare the glass samples (known vs. questioned) and report their findings as they would in casework. The overall correct association rate was greater than 92 % for each of the three techniques (refractive index, µXRF, and LIBS) for samples that were known to originate from the same glass pane. When sample pairs were known to originate from different vehicles, an overall correct exclusion rate of 82 %, 96 %, and 87 % was observed for refractive index, µXRF, and LIBS, respectively. Special attention was given to the reporting language used by practitioners as well as the use of verbal scales and/or databases to assign a significance to the evidence. Wide variations in the reported conclusions exist between different laboratories, demonstrating a need for the standardization of the reporting language used by practitioners. Moreover, few labs used a verbal scale and/or a database to provide a weight to the evidence. It is recommended that forensic practitioners strive to incorporate the use of a verbal scale and/or a background database (if available) to provide a measure of significance to glass forensic evidence.
Forensic Chemistry


forensic glass analysis, interlaboratory study, XRF, LIBS, refractive index


Corzo, R. , Hoffman, T. , Ernst, T. , Trejos, T. , Berman, T. , Coulson, S. , Weis, P. , Stryjnik, A. , Dorn, H. , Pollock, E. , Workman, M. , Jones, P. , Nytes, B. , Scholz, T. , Xie, H. , Igowsky, K. , Nelson, R. , Gates, K. , Gonzalez, J. , Voss, L. and Almirall, J. (2021), An Interlaboratory Study Evaluating the Interpretation of Forensic Glass Evidence Using Refractive Index Measurements and Elemental Composition, Forensic Chemistry, [online], (Accessed April 20, 2024)
Created January 12, 2021, Updated October 28, 2022