Forensics
Hair, Paint, and Fibers
• A. Morphology of hair
– 1. HAIR IS AN APPENDAGE
OF THE SKIN THAT
GROWS OUT OF AN
ORGAN KNOWN AS A HAIR
FOLLICLE.
• 2. The length of hair extends
from its root or bulb
embedded in the follicle,
continues into a shaft, and
terminates at the tip end.
• 3. The shaft is composed of
three layers that forensic
scientist are most interested
in.
– The cuticle, cortex, and
medulla.
• 4. The cuticle is the outer
layer of the hair. It is
composed of overlapping scales
that always point toward the
tip end of the hair. These
scales make the hair resistant
to decomposition and help it
retain its structural features
for long periods of time.
• Hair by itself cannot be
identified to a single person
but it can be used to identify
animal species because of the
differences in scales.
• 5. The layer underneath the
cuticle is the cortex. It is the
main body of the hair shaft.
Its most important forensic
aspect is that it is embedded
with pigment granules that
give its color. This helps with
comparison.
• 6. Medulla is a cellular column
running through the center of
the hair. In some animals this
column takes up a large part
of the hairs diameter. This is
known as the medullary index.
• In humans it is 1/3. The
presence and appearance of
the medulla varies greatly.
• Some have a continuous
medulla.
• Some have interrupted
medulla.
• Some have fragmented
medulla.
• Most human head hair have no
medulla. If present it is
usually fragmented. Except
the Mongolian race who have
continuous medulla.
• There is a searchable
database available which
examines hair based on scale
patterns and medulla type.
• 7. Roots – the root and other
surrounding cells contained
within the hair follicle provide
the tools necessary to produce
hair and continue its growth.
• There are three phases of
hair growth.
• Anagen – 1st phase, may last
up to six years. The hair
follicle is attached to the
root. If the hair is pulled out
with the root attached it will
contain a follicular tag. These
are important for doing DNA
analysis.
• Catagen – 2nd phase. Hair
continues to grow but at a
slower rate. Lasts about 2 to
6 weeks.
• Telogen – the final stage.
Hair growth has stopped.
During a 2 – 6 week period
the hair will be pushed out of
the follicle and shed.
• 8. Identification and
comparison of hair
– The crime lab will be asked
to identify which species the
hair came from or if the
hair came from another
individual involved in the
crime.
• A comparison microscope is
used for this task.
• They may be able to identify
chemicals on the hair or when
the hair was last dyed.
• Hair grows at an average of I
cm per month. Other factors
learned from examination
include disease, infection, or
drug use.
• 9. Can the body area from
which a hair originated be
determined? Yes, by looking
at pigmentation, courseness,
diameter and tips.
• 10. Can the racial origin of
hair be determined?
• Usually
• African
Caucasian
*Pigment is
dense and
unevenly distributed
*Very fine to
coarse pigments
evenly distributed
*Flat to oval
cross-section
*Oval crosssection
• 11. Can the age and sex of an
individual be determined from
hair?
• Age can only be determined
for infants.
• The recovery of DNA can
prove male or female origin.
• 12. Is it possible to determine
if a hair was forcibly removed
from the body?
• A hair root that has follicular
tissue adhering to it is
indicative of a hair that has
been pulled out. Hair that
falls out naturally will have a
root free of tissue. However,
hair that is pulled out slowly
is less likely to have root
tissue that hair pulled out
quickly.
• B. Fibers
• 1. Natural fibers are derived
in whole from animal or plant
sources. Animal fibers account
for the majority of natural
fibers encountered in the
crime lab.
• These include hair coverings
such as wool, mohair,
cashmere, mink, etc. The
procedure for analyzing these
is basically the same as that
for hair.
• The most common plant fiber
is cotton. Unfortunately the
wide use of this makes it hard
to use as evidence.
•
• 2. Man-made fibers. These
are fibers derived from either
natural or synthetic polymers.
The fibers are typically made
by forcing the polymer
material through the hole of a
spinneret.
• Most of the fibers currently
manufactured are produced
solely from synthetic
chemicals and are therefore
classified as synthetic fibers.
Examples include nylon,
polyester, and acrylics.
• 3. The polymer is the basic
chemical substance of all
synthetic fibers. Polymers are
long-chained molecules.
Examples of things
manufactured from polymers
are plastics, paints,
adhesives, and rubber.
• 4. The first step in analysis
of a fiber is microscopic
comparison for color, shape,
and size using a comparison
microscope.
• The second step would be to
analyze the dye or dyes
present on the fibers.
• The last phase of comparison
is to determine if two fibers
are chemically identical.
• C – Forensic Examination of Paint.
• 1. One of the most commonly
encountered types of physical
evidence, most frequently in hitand-run and burglary cases.
Usually the forensic scientist will
be asked to compare two or more
paints for the purpose of
determining common origin.
• 2. The paint from an
automobile can be used to
determine the color, make,
and model of a car.
• 3. What is paint made of?
• Paint is composed of pigments
(to give color and hiding
quality) and a binder which
provides the support medium
for the pigment and other
additives. The binder is
usually a polymer.
• 4. Automotive paint – there
are four basic coatings for
auto paint.
– a. The ELECTROCOAT
PRIMER is the first layer.
It is electroplated onto the
steel body to provide
corrosion resistance. Usually
grey or black in color.
– b. The PRIMER SURFACER
is applied over the
electrocoat primer. Its
function is to smooth out and
hide seams or imperfections.
– Color differs.
– c. The BASECOAT is the
layer that provides the color
and appearance of the
finish. Mica pigments,
aluminum flakes, and other
materials are added to give
paint an individual and unique
appearance.
– d. The CLEARCOAT has no
color and is used to provide
gloss and add durability.
• The microscope has
traditionally been and remains
the most important instrument
for locating and comparing
paint specimens.
• Color imparts paint with its
most distinctive forensic
characteristics.
• The importance of layer
structure for evaluating the
evidential significance of paint
is very important.
• When paint specimens posses
colored layers that match with
respect to number and
sequence of colors a common
origin can is probable.
• The diverse chemical
composition of paint can
provide for additional points
of comparison between
specimens.
• A thorough comparison of
paint must include a chemical
analysis of either the paint’s
pigment, binder, or both.
• Pyrolysis gas chromatography
is a valuable and accepted
technique for distinguishing
most paint formulations. In
this process paint chips as
small as 20 micrograms are
decomposed by heat into
numerous gas products.
• These products are sent
through a gas chromatograph.
What emerges and is recorded
are the separated
decomposition products of the
polymer used in the paint.
• It is the pattern of this
chromatogen or “pyrogram”
that distinguishes one polymer
from another. What results is
a pyrogram that is sufficiently
detailed enough to reflect the
chemical make-up of the
binder.
• Infrared spectrophotometry is
another analytical technique
used to provide information
about the binder composition
of paint. Binders will
selectively absorb infrared
radiation to yield a spectrum
that is highly characteristic of
a paint specimen.
• The elements that comprise
the inorganic pigments of paint
can be identified by either
emission spectroscopy, neutron
activation analysis, X-ray
diffraction, and X-ray
spectroscopy. The emission
spectrograph can
simultaneously detect 15 to 20
elements in most automobile
paint.
• Crime labs are often asked to
identify the make and model
of a car from a very small
amount of paint left behind at
a crime scene.
• Color charts for automobile
finishes are available from
paint manufacturers.
• Starting in 1974 the Law
Enforcement Standards
Laboratory has collected and
given out to crime labs auto
paint samples from domestic
passenger cars.
• The data collected from crime
scenes can be compared to
data in the Paint Data Query
Database to determine
possible make, model and year
of the paint.
• End