CHAPTER 10
HAIR AND FIBER
BASIC HAIR STRUCTURE
• Basic components:
keratin (a protein),
melanin (a pigment),
and trace quantities of
metallic elements (Cu,
Fe, Mn,etc).
• Elements are deposited
in hair during growth
and absorbed by the
hair from external
environment.
More on Hair Basics
• All 5 million hair follicles are
formed by week 22 during fetal
development.
• 100,000 follicles on the scalp.
• You have the most follicles
when you are born – as body
size decreases with age so does
the number of hair follicles –
NEVER get any new ones
• Hair is found on all visible body
surfaces.
• Hair is the only structure that is
completely renewable without
scarring
• Hair goes about 0.5 inch per
month (~ 6 inches per year)
HAIR STRUCTURE BELOW THE SKIN
HAIR SHAFT
Cuticle – First Layer
• The cuticle is a
translucent outer
layer of the hair
shaft consisting of
scales that cover the
shaft.
• The cuticle scales
always point AWAY
from the root end toward the tip of the
hair.
CUTICLE SCALES:
CORONATE
FREE-TAILED BAT HAIR
• Scales show crownshaped pattern
• Found in small rodents
and bats
• Coronate pattern
NEVER seen in
human hair
CUTICLE SCALES: SPINOUS
• Spinous - petal-like
scales are triangular in
shape and protrude
from the hair shaft.
• Spinous are found close
to the body on mink,
and on seals, sea lions,
fox and cats
• Never found in humans.
CUTICLE SCALES: IMBRICATE
• The imbricate (bricklike) or flattened scales.
Consists of tightly
overlapping scales with
narrow margins
between the scales.
• Usually only found in
human hair (some
animal species).
HAIR SHAFT
Cortex – Second Layer
• The area between
the cuticle and the
core of the hair.
• Contains all the
pigment granules,
ovoid bodies and
any moisture
PIGMENT GRANULES
• Pigment granules are small, dark, and solid structures
that look like grains of sand
• They contain melanin
• In humans, pigment granules are found in the cortex
closest to the cuticle
• Animal hairs have pigment granules only in the medulla.
Human
Rat
HAIR SHAFT
Medulla – Center Layer
• The medulla is a central
core of cells that may
be present in the hair.
• Human hair - the
medulla unorganized,
random pattern
• Animal hair - structure
is well defined
• Some medullary
patterns:
CONTINUOUS
INTERRUPTED
FRAGMENTED
ABSENT
Continuous Medulla
• Medulla has solid
continuous medulla
through the entire
hair shaft.
• No breaks or gaps
Upper - human hair
Lower - lattice pattern
of a deer
Medulla - Interrupted
• Pattern is repeated over and over in the hair shaft at
regular intervals.
• Common in rodent hair (rats, mice, guinea pigs,
ferrets, bats)
Guinea Pig
Multiserial ladder (rabbit)
Mouse
FE
Ferret
FRAGMENTED
• Bubbly or cellular medullary area
• Center of hair shaft appears hollow with bubble or cell-like
pattern but can have a few parts visible
• Most common in human hair but can be found in animals
Human
Cow
Absent Medulla
Human
• No discernable
medulla visible
• Can be found in
human hair and
animal hair
Human
Silver fox
ANIMAL HAIRS
Animal hair always has a medullary index of 1/3 or greater.
Animal roots are usually rounded in shape.
Animal hairs are classified into the following four basic types.
• Guard hairs that form the outer coat of an animal and provide
protection
• Fur or wool hairs that form the inner coat of an animal and
provide insulation
• Tactile hairs (whiskers) located on the head provide sensory
functions
• Types of hairs found on animals include tail hair and mane hair
(horse, zebra).
HUMAN HAIR
• The root is club-shaped
• Consistent in color and
pigmentation throughout
the length of the hair
• Medullary index is less
than 1/3
• Pigment is evenly
distributed, slightly more
dense near the cuticle
Pigment Distribution in Human
Hair
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Brown Human Hair
•
Red Human Hair
Pigment granules are small,
dark, and solid structures
They vary in color, size, and
distribution in a single hair.
In humans, pigment granules
are commonly distributed
toward the outer edge of cortex
The exception is red-haired
individuals, granules are
concentrated along the center of
the hair
Scale Casts
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Scale casts may also be prepared
using clear nail polish.
A thin coat is painted on a glass
microscope slide or, if the lacquer is
thinned with acetone, a drop may be
allowed to run down the surface of
the slide.
The hair is placed on the slide and
allowed to dry.
When the surface has dried, the hair
is removed to reveal the scale
pattern.
Scale Cast of Human Hair
Microscope Slide Preparation
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Positioning a hair on the glass slide
by first applying a thin film of nail
polish on the slide surface.
Longer hairs are placed in a figure
eight in order to fit it under the cover
slip. This enables the examiner to
view the entire hair from root to tip.
Several drops of mounting medium
are applied on top of the hair
A cover slip is carefully lowered to
prevent the presence of air bubbles.
It may be necessary to apply some
weight to the cover slip in order to
ensure a thin mount.
Caucasian-Origin Hair
•
Shaft diameter: moderate with
minimal variation (mean
diameter for human head hairs 80um)
•
Pigment granules: sparse to
moderately dense with fairly
even distribution
African-Origin Hair
• Shaft diameter: moderate
to fine with considerable
variation
• Pigment granules: densely
distributed (hair shaft may
be opaque) and arranged
in prominent clumps
• Shaft: prominent twist and
curl
Asian-Origin Hair
•
Shaft diameter: coarse and
usually with little or no
variation
•
Pigment granules: densely
distributed and often
arranged in large patchy
areas or streaks
•
Medulla: prominent (often
broad and continuous)
•
Cuticle: thick
FIBERS
Types of Fibers
• Natural fibers are derived in whole from animal or
plant sources.
– Examples: wool, mohair, cashmere, furs, and cotton.
• Man-made fibers are manufactured.
– Regenerated fibers are manufactured from natural raw
materials and include rayon, acetate, and triacetate.
– Synthetic fibers are produced solely from synthetic
chemicals and include nylons, polyesters, and acrylics.
• Polymers, or macromolecules, are synthetic fibers
composed of a large number of atoms arranged in
repeating units known as monomers
Natural Fibers
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Fibers that are from plant or
animal sources
Cotton fibers are the most
common plant fibers
Other plant fibers used in the
production of textiles include
flax (linen), ramie, sisal, jute,
hemp, kapok, and coir
The most common animal
fiber is wool that is taken
from sheep.
Woolen fibers from other
animals include camel,
alpaca, cashmere, mohair
Cotton fibers
Wool Fibers
Flax fibers
Synthetic Fibers
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More than half of all fibers
used in the production of
textile materials are manmade.
Polyester and nylon fibers are
the most commonly
encountered man-made
fibers, followed by acrylics,
rayons, and acetates.
The shape of a man-made
fiber can determine the value
placed on that fiber.
The cross section of a manmade fiber can be
manufacturer-specific
Acetate
Luxurious feel, appearance
Wide range of colors
Shrink, moth & mildew
resistant
Acrylic
Soft, warm
Wool-like
Fiber retains shape
Resilient
Quick-drying
Shrink, moth, fade resistant
Aramid
Great strength
Stretch resistant
Does not melt
Highly flame-resistant
Fibers maintain shape and
structure even at very high
temperatures
Lyocell
Soft, strong absorbent
Easily dyed
Fiber can be made into many
textures
Melamine
White fiber, easily dyed
Flame resistant
Does not conduct heat
Plastic used to make “unbreakable”
Dishes
Used to make airplane seats
Firefighter’s protective wear
Nylon
Early man-made fiber
(1930’s)
Very strong fiber
Supple fabric
Resilient, holds it’s shape
Abrasion-resistant
Lustrous fabric
Water-resistant
Oil and chemical resistant
Used to make seatbelts,
clothing, carpets, bedding,
drapes, parachutes, tents
Polyester
Rayon
First manufactured in 1911
Spandex
Fiber Evidence
• The quality of the fiber evidence depends
on the ability of the criminalist to identify
the origin of the fiber or at least be able to
narrow the possibilities to a limited number
of sources.
• Obviously, if the examiner is presented with
fabrics that can be exactly fitted together at
their torn edges, it is a virtual certainty that
the fabrics were of common origin.
Fiber Evidence
• Microscopic comparisons between questioned and
standard/reference fibers are initially undertaken
for color and diameter characteristics, using a
comparison microscope.
• Other structural features that could be important in
comparing fibers are:
– Lengthwise striations on the surface of the fiber.
– The presence of delustering particles that reduce shine.
– The cross-sectional shape of the fiber.
• Compositional differences may exist in the dyes that were
applied to the fibers during the manufacturing process.
Fiber Analysis
• The visible light microspectrophotometer is a
convenient way for analysts to compare the colors
of fibers through spectral patterns.
• A more detailed analysis of the fiber’s dye
composition can be obtained through a
chromatographic separation.
• Infrared spectrophotometry is a rapid and reliable
method for identifying the generic class of fibers,
as does the polarizing microscope.
• Depending on the class of fiber, each polarized
plane of light will have a characteristic index of
refraction.
Evidence Collection
• The investigator’s task of looking for
minute strands of fibers often becomes one
of identifying and preserving potential
“carriers” of fiber evidence.
• Relevant articles of clothing should be
packaged carefully in separate paper bags.
• If it is necessary to remove a fiber from an
object, the investigator must use clean
forceps, place it in a small sheet of paper,
fold and label the paper, and place the paper
packet inside another container.