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Typical Evidence Examination Scheme

 

 

 

 

 

 

 Fibers

 Paint

 Adhesive Tape

 Muzzle to Target Distance

 Unknown Materials Identification

 Latent Fingerprint Development

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.  

 

 

 Glass fragment, plane polarized light

 Glass fragment refractive index 1.559, mounted in 1.410 refractive index oil



 

 

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  

Glass fragment refractive index 1.559, mounted in 1.560 refractive index oil,  notice the poor contrast 


 

 

Glass fragment refractive index 1.559, mounted in 1.638 refractive index oil

 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


 

 

Quartz, plane polarized light  

Quartz, crossed polars  


 

 

 

Quartz, omega refractive index view

Quartz, uniaxial interference figure

Quartz, uniaxial positive interference figure, "red" wave plate inserted


 

 

Calcite, crossed polars

Calcite, crossed polars, rotated to show symmetrical extinction