Standard Guide for Forensic Collection, Analysis, Comparison, and Evaluation of Glass

Importancia y uso:

5.1 This guide is intended to assist the FSP in collecting glass evidence, then selecting and organizing an analytical scheme for identifying, analyzing, and comparing glass samples.

5.2 Glass fragments can be assessed for morphological (curvature, thickness, coatings, color, fluorescence), optical (refractive index), and chemical properties (elemental composition). Refer to Test Methods E1967, E2926, E2927, and E2330, which can be used to determine glass refractive index or elemental composition.

5.3 Glass fragment morphological properties, refractive index, and elemental analysis can be used to constrain the class or end-use of the glass.

5.4 For a glass comparison, glass fragments are assessed for physical fit of fracture surfaces and for similarities in morphological properties, refractive index, and elemental composition.

5.4.1 Physical fit of glass fragments indicates having been derived from the same object (see 11.6).

5.4.2 Observed differences in morphological properties, refractive index, and elemental composition that exceed the estimated source variability and analytical precision serve as exclusionary differences to determine that glass fragments were derived from different sources.

Note 1: Exclusionary differences in physical properties, optical properties, and elemental composition of glass samples can be attributed to the glass being manufactured in different plants/lines or manufactured in the same plant/line at different time intervals or with different end-product characteristics (for example, thickness), or in post-production processes (for example, tempering, coating).

Note 2: In this context throughout this guide, “source” refers to the original glass object.

5.4.3 Similarities in morphological properties, refractive index, and elemental composition between glass fragments can be used to determine association between broken glass sources with the same class characteristics. The combination of sensitive elemental analysis methods and refractive index determination provides high discriminating power between different sources of glass.

5.4.4 This guide offers a framework for interpretation of forensic glass comparisons.

Note 3: Publications by Trejos et al. (4), Almirall and Trejos (5), Bottrell (6), Caddy (7), Curran (8), and Koons et al. (2) provide more detailed information on forensic glass analysis.

5.5 Fracture reconstruction can be used to reassemble the shape of the unbroken glass object.

5.6 Fracture analysis can be applied to assess type and direction of breaking force; approximate angle of incidence; point(s) of impact; and sequence of impact occurrence.

Subcomité:

E30.15

Volúmen:

14.02

Palabras clave:

forensic science; glass; glass comparison; instrumental analysis;