The forensic examination of glass typically includes refractive index and elemental analysis, which have been optimized for soda-lime glass comparisons, because that glass type is frequently found at crime scenes. Despite its increased prevalence in everyday life and potential relevance in criminal investigations, standard test methods have yet to be adapted for portable electronic devices (PED) made of aluminosilicate glass. This study addresses this need by providing recommendations regarding refractive index (RI) and micro-X-Ray Fluorescence (µXRF) analysis of glass fragments recovered from contemporary PED screens. Glass from 48 modern cellular phones from six popular manufacturers was sampled, and within and between-screen variation was assessed for RI and µXRF. The most significant finding of this study is that different sampling, analytical protocols, and comparison criteria are necessary to account for variations in the optical properties and elemental profiles of aluminosilicate glass. It is recommended that 30 total measurements obtained from at least 10 fragments be collected to properly characterize the known sample, thereby reducing error rates. For refractive index measurements, the false exclusion and inclusion rates were less than 3 % and 9 %, respectively, when using a range overlap criterion. For µXRF measurements, using a modified 5 s comparison criterion for element ratio comparisons produced low false exclusion and false inclusion rates (less than 4.0 % and 0.5 %, respectively). In this dataset, the combination of RI and µXRF yielded a 99.9 % discrimination of glass originating from different sources. Additionally, the most informative elements for PED characterizations are discussed here to assist analysts in interpreting the data.
(Publisher abstract provided.)