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Typical Evidence Examination Scheme
Unknown Material ID
The Trace Evidence Department may be called upon to identify an unknown material. The source of the unknown material could be from autopsy, collected at a crime scene, or collected by the Trace Evidence Scientists themselves. The examination of unknown materials is made problematic because the material could literally be anything. It is important for the Trace Evidence Scientist to gather as much information about the history of the material as possible. The location it was collected from, the environment surrounding the sample, the nature of the crime, and any reaction between the sample and its substrate are but a few areas of information that may shed some light upon the unknown material. Whatever information is obtained, a logical approach to the identification of the material is essential. The examination of an unknown material should progress from a macroscopic examination to a microscopic examination and is then finished with a chemical, physical, and/or instrumental analysis.
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Glass fragment, plane polarized light
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Glass fragment refractive index 1.559, mounted in 1.410 refractive index oil
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Glass fragment refractive index 1.559, mounted in 1.410 refractive index oil, above sharp focus, notice the becke line has moved into the glass fragment
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Glass fragment refractive index 1.559, mounted in 1.560 refractive index oil, notice the poor contrast
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Glass fragment refractive index 1.559, mounted in 1.638 refractive index oil
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Glass fragment refractive index 1.559, mounted in 1.638 refractive index oil, above sharp focus, notice the becke line has moved away from the glass fragment
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Quartz, plane polarized light
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Quartz, crossed polars
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Quartz, omega refractive index view
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Quartz, uniaxial interference figure
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Quartz, uniaxial positive interference figure, "red" wave plate inserted
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Calcite, crossed polars
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Calcite, crossed polars, rotated to show symmetrical extinction
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