Forensic Examination of Fibers
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Important evidence in
incidents involving personal
contact- homicide, assault,
sexual
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Cross-transfers may occur
between the clothing of a
suspect and victim
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Hit-and-run victims can leave
fibers, threads, or whole
pieces of clothing on a vehicle
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Fibers can also become fixed
in screens or glass broken
during a breaking-andentering attempt
Natural Fibers
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Are derived from animal or plant
sources
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Animal fibers comprise most natural
fibers encountered in crime lab exams
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Can include hair coverings: sheep
(wool), goats (cashmere), camels,
llamas
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Or fur fibers: obtained from mink,
rabbit, beaver, etc.
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Most common plant fiber is cotton
Manufactured Fibers
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1)
2)
3)
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Are derived from natural or synthetic polymers
They have increasingly replaced natural fibers in
clothing & fabric
They are made by:
Processing raw material from cotton/wood pulp and
extracting cellulose
The cellulose may be chemically treated and
dissolved in a solvent
It is then forced through small holes of a spinning jet
(spinneret) to produce the fiber
Fibers made from natural raw materials (regenerated
cellulose) are called regenerated fibers: rayon,
acetate, triacetate
Fibers made from synthetic chemicals are synthetic
fibers: nylon, polyester, acrylic
Microscopic Exam of Fibers
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The first and most important step is
a comparison for color & diameter
by a comparison microscope
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Other features that may aid in the
comparison are lengthwise
striations (lined markings) on the
surface of some fibers and pitting of
the fiber’s surface with delustering
particles (titanium dioxide particles
added to reduce shine)

Cross-sectional shape of a fiber
may also help
Analytical Techniques Used
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Two fibers may seem to be the
same color, differences may exist
in the dyes applied to them when
made

Most fibers are dyed with a
mixture of colors to obtain a
desired shade

Can use a visible light
microspectrophotometer to
compare the colors of fibers

A fiber as small as 1 mm long or
less can be examined
Analytical Techniques Used

A more detailed analysis of the fiber’s
dye composition can be obtained by
a chromatographic separation of dye

Small strands of fibers are compared
for dye content by extracting the dye
off each fiber with a solvent and then
spotting the dye solution onto a thinlayer chromatography plate
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The dye of the questioned and
standard fibers are separated on the
plate and compared for similarity
Others
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When fibers are compared, they must be
shown to have the same chemical
composition (belong to the same class)

For example, the standard and questioned
fabric both being nylon instead of one
being nylon while the other is cotton
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Many manufactured fibers exhibit double
refraction or birefringence which will make
it look crystalline

Polarized white light will split into two rays
that are perpendicular to each other and
produce interference colors, polarization
Significance of Fiber Evidence
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Once a match has been determined, the
significance is bound to be raised
No technique can associate a fiber definitively to
any single garment
No database is available for determining the
probability of a fiber’s origin
Despite this, one should not discount the
significance of a fiber match
By observing what people wear, it is unlikely to
find two different people wearing identically
colored fabric ( exception: jeans and cotton tees)
There are thousands of different colored fibers
Combine this with the fact that scientists not only
compare color, but also size, shape, microscopic
appearance, chemical composition and dye
There will still be a good chance of linking a
questioned fiber to a standard
Collection and Preservation
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Clothing should be packaged in paper bags
Each article must be placed in separate bags to
prevent contamination
Must keep clothing from different people from
coming into contact
Carpets, rugs, and bedding should be folded to
protect areas suspected of containing fibers
Knife blades should be covered to protect
adhering fiber
If a body was wrapped in a carpet or blanket,
tape lifts must be done on the body
If individual fibers are found, they must be
removed with clean forceps and placed in a
small sheet of paper, must be folded and
labeled and placed in another container
Types of Fiber
Cotton (ribbon-like)
Rayon fibers
Nylon
Polyester
Silk (fractures)
Wool