Transcript Hair, Fiber, and Paints - Anchorage School District

Hair, Fiber, and Paints
Morphology and Structure of
Hair
Morphology: Cuticle
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Protective coating made of overlapping
scales, produce a characteristic pattern
Scales always point toward tip of hair
Not useful in individualizing human hair
Can be used for species identification
Preserving scale pattern
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Since examination of
internal structure of hair
requires loss of scale
pattern, a scale case is
made.
Clear nail polish on
microscope slide
Hair embedded and
allowed to dry before
removed.
Morphology: Cortex
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Made of spindle-shaped cells aligned in
a regular array, parallel to the length of
the hair
Embedded with pigment granules that
give hair its color
The color, shape and distribution of the
granules provide points for forensic
comparison
Morphology: Cortex (cont’d)
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In order to examine the cortex of the
hair, it is suspended in a liquid with a
refractive index similar to that of the
hair.
Morphology: Medulla
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canal like structure of cells that runs
through the center of the cortex
Medullary Index
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Measure of the diameter of the medulla
relative to the diameter of the hair shaft
Usually expressed as a fraction
Humans: medullary index < 1/3
Animals: medullary index > 1/2
Medulla of
Different
Species
Forensic Analysis of Medulla
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Presence of medulla varies quite a bit: even hair to
hair
Human head hairs generally have no medulla or may
be fragmented ones; except Mongoloid (Asian) race
whose medulla is usually continuous
Most animals have medulla that is continuous or
interrupted
The shape of the medulla can help identify a species
Examples:
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Most animals and humans: cylindrical
Cats: pearl shape
Deer: spherical occupying whole hair shaft
Identification and Comparison
of Hair
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Morphological Characteristics do not allow individualization
of a human hair to any single head or body
Hair when collected with an adequate number of
standards/references can provide strong circumstantial
evidence
Scale structure, medullary index, and medullary shape are
most often used for hair comparison
Evidential value lies with degree of probability associated
with a questioned hair and a particular individual
11 percent of all morphological hair matches are generally
found to be non-matches—meaning microscopic hair
comparisons are presumptive in nature—must be
confirmed by DNA comparisons
Hair type
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Scalp hair has consistent diameter and
uniform distribution of pigment
Pubic hairs have continuous medullae
Beard hairs have triangular crosssections
Eyebrow hair has decreasing diameter
from root to tip
Can the racial origin of hair be
determined?
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Anthropological terms: Caucasian, Negroid,
Mongoloid
Mongoloid has continuous medullae
Caucasian has even distribution of pigment in
cortex
Negroid has unevenly distributed pigment.
Root:
Human hair grows in three developmental
stages: anagen, catagen, and telogen phases
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Initial growth phase during which hair follicle
is actively producing hair, phase may last 6
years, root is flame like in appearance
When pulled this root may contain a follicular
tag, which is a rich source of DNA
Anagen hair root
Root w/ follicular tag
Fibers: Natural
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Derived entirely from animal or plant sources
Most prevalent plant fiber is cotton.
Its widespread use has made its evidential
value almost meaningless
Cotton has a ribbon-like shape with twists at
regular intervals (see text for picture)
Animal sources include sheep (wool), goats
(mohair, cashmere) and many other sources
Man-Made Fibers
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Fibers derived from either natural or
synthetic polymers
The fibers are made by forcing
polymeric material through the holes of
a spinneret
Rayon and then nylon were the first two
man-made fibers (year 1911)
Man-Made Fibers Con’t
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Regenerated Fibers
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Made from regenerated cellulose (wood or cotton
pulp)
Include such fibers as rayon, acetate, and
triacetate
Synthetic Fibers
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Currently manufactured
Made from synthetic chemicals called polymers
Include such fibers as nylons, polyesters, and
acrylics
Polymers
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Basic chemical substance of all synthetic
fibers
Consist of long chains of repeating molecules.
The repeating molecular units in the polymer
are called monomers. (see pic p210)
Often referred as macromolecules or “big”
molecules
Countless varieties exist
ID and Comparison of ManMade Fibers
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Fabrics that can be fitted together at their torn edge
are easy to match
Microscopic comparison of color and diameter
Comparison of lengthwise striations and pitting on
the surface of a fiber
The shape of the fiber—ex. Wayne Williams case
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Cross sections are generally helpful
Note: Combined factors of color, size, shape,
microscopic appearance, chemical composition, and
dye content make it very unlikely to find two different
people wearing identical fabrics
Tools and Techniques to Aid in
Comparing Fibers
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UV-Vis or IR spectrophotometer—compares
colors and chemical composition through
spectral patterns
Chromatography—compares dye composition
Refraction—ID’s fiber by refractive index
Comparison microscope—reveals shape,
coloring, pitting and striations
Visible
spectrophotometry
IR spectrum of wig hair
Chromatography
Forensic Examination of Paint
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Paint evidence is frequently
encountered in hit-and-run and burglary
cases
Most examinations consist in comparing
two or more paints to establish their
origin
Often color, make and model of a
vehicle can be determined
Paint Characteristics
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Paint spread on a surface will dry into a hard film consisting of
pigments and additives suspended in a binder
The binder provides the support medium for the pigments and
additives.
Modern automotive finishing consists of at least four coatings:
Electrocoat Primer: first layer, electroplated to the car—provides
corrosion resistance—color from black to grey
Primer Surface: second layer, smoothes out and hides any
seams on the car—color pigments are used to minimize contrast
between primer and topcoats
Basecoat: third layer, provides the basic color and appearance of
the car
Clearcoat: final coat, provides great appearance (glossiness)
and protection for the car
Tools and Techniques to Aid in
Paint Examination
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Questioned and known specimens are compared side by side under a
stereomicroscope for color, surface texture, and color layer sequence
Note: Layer sequence is very important evidence: forensic scientists
will try to match layers with respect to number and sequence of color
Note: Layer structure alone will not provide enough information to be
individualized to a single source
Chemical analysis of the paint’s pigments and binder composition
provides further points of comparison.
Typically, gas chromatography is used to determine the chemical makeup of the binder material.
Infrared spectrophotometry is also used to determine the binder
composition of paint.
Elements of the paint pigments can be identified with a number of
techniques, including Visible spectroscopy
Using these techniques the odds against crime-scene paint originating
from another randomly chosen vehicle is approximately 33,000 to one.
Spectroscopy can be used to identify
paint samples