Elemental analysis of glass fragments
2001; CRC Press; Linguagem: Inglês
10.1201/9780203483589.ch4
ISSN2475-4021
Autores Tópico(s)Geophysical Methods and Applications
ResumoGlass examiners in forensic laboratories have found it useful to incorporate elemental analysis as part of their routine examination and evaluation of glass evidence. The value of the measurement of major, minor and trace elemental composition of glass for its classification into glass types has been recognised for some time [1–4]. It is usually helpful to be able to classify the questioned glass into one of a number of possible categories, such as sheet (or ‘float’, the name of the process for the manufacture of most sheet glass), container, vehicle window (also made by the float process), vehicle headlamp (a borosilicate glass) or tableware (including leaded glass). One reason for classification is to facilitate the assessment of the association between the questioned and the known fragments by either classifying both as the same type of glass and then applying the appropriate comparison criteria or by eliminating straight away the questioned fragment from originating from the known source. Technological advances in the manufacture of glass and the improved quality control in the glass industry has led to less variability in physical and optical properties between the manufacturers of products and also to less variability between the different plants from the same manufacturer. Through the use of the computer-controlled delivery of raw materials and the sophisticated on-line monitoring of the manufacturing lines, the glass manufacturing industry has aimed to control the differences in density, refractive index, thickness, colour and toughening (tempering) properties. The result of this improved quality in the manufacture of glass has been an industry-wide narrowing in the ranges of physical properties in glasses of the same type. Consequently, the discrimination potential, or the ability to distinguish between glass fragments, has been diminished and the sole reliance on measurements such as density and refractive index can lead to overstating the value of positive ‘matches’. For example, recent studies show that for float glass sampled on three separate occasions over a period of 18 months from the same United States plant, the refractive index was found to be analytically indistinguishable [5] when using a precise method for the measurement of refractive index. Consequently, a number of publications have been
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