FRSC 1011H Chapter Notes - Chapter 14: Forensic Science, Pyrolysis, Spectrophotometry
2 May 2018
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Trace Evidence Paint, Glass and Soil
Forensic Examination of Paint
● Paint spread onto a surface dries into a hard film that is best described as
consisting of pigments and additives suspended in a binder.
● Questioned and known paint specimens are best compared side by side under a
stereoscopic microscope for color, surface texture, and color layer sequence.
● Pyrolysis gas chromatography and infrared spectrophotometry are used to
distinguish most paint binder formulations.
● Paint Data Query (PDQ) is a computerized database that allows an analyst to
obtain information on paints related to automobile make, model, and year.
Forensic Analysis of Glass
● To compare glass fragments, a forensic scientist evaluates density and refractive
index.
● The “immersion method” is used to determine a glass fragment’s refractive index.
It involves immersing a glass particle in a liquid medium whose refractive index is
adjusted by varying its temperature. At the refractive index match point, the
visual contrast between the glass and liquid is at a minimum.
● The “flotation method” is used to determine a glass fragment’s density. It involves
immersing a glass particle in a liquid whose density is carefully adjusted by
adding small amounts of an appropriate liquid until the glass chips suspends in
the liquid medium.
● By analyzing the radial and concentric fracture patterns in glass, the forensic
scientist can determine the side of impact by applying the 3R’S rule: Radial
cracks form a Right angle on the Reverse side of the force.
Forensic Analysis of Soil
● A side by side visual comparison of the color and texture of soil specimens
provides a way to distinguish soils that originated from different locations.
● Minerals are naturally occurring crystalline solids found in soil. Their physical
properties-for example, their color, geometric shape, density, and refractive
index-are useful for characterizing soils
Document Summary
Paint spread onto a surface dries into a hard film that is best described as consisting of pigments and additives suspended in a binder. Questioned and known paint specimens are best compared side by side under a stereoscopic microscope for color, surface texture, and color layer sequence. Pyrolysis gas chromatography and infrared spectrophotometry are used to distinguish most paint binder formulations. Paint data query (pdq) is a computerized database that allows an analyst to obtain information on paints related to automobile make, model, and year. To compare glass fragments, a forensic scientist evaluates density and refractive index. The immersion method is used to determine a glass fragment"s refractive index. It involves immersing a glass particle in a liquid medium whose refractive index is adjusted by varying its temperature. At the refractive index match point, the visual contrast between the glass and liquid is at a minimum. The flotation method is used to determine a glass fragment"s density.
