1. Dr. Sangeetha Balakrishnan
PG Department of Chemistry
Women’s Christian College
Chennai – 600 006
Fibers and Hair
4 February, 2017
Forensic Science
PCH/NM/01
2. Fibers
• Fibers are a trace evidence.
• Direct Transfer: Transfer of fibers directly
from victim to suspect or suspect to victim.
Eg: fiber from woolen sweater of victim
attacker
• Secondary Transfer: Fibers are transferred
from the original source to a suspect and
then to a victim.
Eg: carpet fiber victim attacker
3. Classification of Fibers
Fibers
Natural Synthetic Mineral
Animal
Animal Plant
Silk – silkworm
Cashmere – goats
Angora – rabbits
Obtained from
hair/fur of the animals.
Animal fibers are
made of proteins.
Plant fibers are
made of cellulose.
Seeds - cotton
Fruits – Coir (coconut)
Stems – hemp, jute, flax
Leaves – banana, manila
(man-made fibers)
Mineral fibers are
neither made of proteins
nor of cellulose.
They are obtained from
naturally occurring
minerals.
Asbestos fiber
9. Analysis of Fibers
1. Observation of Fiber Cross Section -
Microscopy
• Type of cross section helps identify the fiber.
• Fibers made with end use in mind!
Trilobal cross-section: more volume, sheen and better resilience.
True delta cross-section: extra brightness and shine.
Round cross-section: smooth silky luster.
Hollow cross-section: light weight and improved insulation.
10. 2. Diameter
• Round fibers: one diameter
• Many fibers are not round!
• Oval and elongated fibers have more
than one diameter!
• Both the diameters are recorded!
11. 3. Delusterants
• Finely ground materials added to the
chemical mixture from which the fiber is
made.
• Act to reduce the fiber's shine, by
scattering light.
• Eg: Titanium dioxide
• Delusterants of different shapes and sizes
added to the pre-fabrix mix.
• Observation of these delusterants in the
unknown evidence and known evidence.
12. 4. Refractive Index
• Submersion Method.
• The shape of the fiber may cause it to
have more than one refractive index.
• Reason: light travels at different speeds in
the fiber depending on whether it travels
through the length and diameter of the
fiber.
RI1
RI2
14. Chemical Analysis of Fibers
1) Fourier Transform Infrared
Spectroscopy (FT-IR)
• non-destructive fiber analysis
• identifies the chemical composition of
fibers.
• not just the class, but also the sub-class to
which the fibers belong!
• Nylon 6-6 and Nylon 6-12.
15. 2) Pyrolysis Gas
Chromatography
• Requirement: Just about 1/8th of a fiber.
• Destructive analysis mode.
• Betterthan FT-IR in distinguishing closely
related fibers.
17. Hair
• Also a trace evidence. Like fiber.
• Importance to forensic scientists:
Easily transferred.
Multiple transfers; help create a trail.
It is stable; can be found years after
someone is buried in a casket.
Mostly resistant to chemical attack.
Has mitochondrial DNA. Unique
identification!
18. What is hair?
• Hair is found only in mammals.
• Hair is an outgrowth of the
epidermis.
• Hair originates at follicles.
• As hair begins to grow, it is soft.
When it reaches the epidermis, it
hardens into keratin.
• Papilla: present at the end of the
follicle. Supplies nutrients to hair.
• Sebaceous gland: secretes oil to
keep hair conditioned.
19. Hair - The Basics (cont'd)
• Hair absorbs nutrients and "materials" at
follicle as it grows. These are supplied by
the blood vessels.
• At the surface of the skin, hair is
keratinised; it is dead. It no longer receives
supplies from the blood vessels.
• Hair growth: hair is "pushed up".
• "material" absorbed by hair at follicle
remains in hair as it is "pushed up", and
until the hair is cut or falls out.
• Example: Tetrahydrocannabinol absorbed
from marijuana. --->Drug analysis on hair!
20. The Structure of Human Hair
• Root: widest end of the hair.
It is the part that was growing in the follicle.
• Shaft: From the root to the tip, it tapers.
• Tip: End of the hair away from the root.
Hair is narrowest at the tip.
Hair has different diameters depending on
where it is measured.
21. The Structure of Human Hair (cont'd)
cuticle
• outermost layer
• made of keratin
• not smooth
• overlapping scales.
cortex
• middle layer
• humans: most prominent
• made of spindle cells
• melanin: here!
medulla
• innermost layer
• in humans:
4 types found.
25. The Life Cycle of Hair
• 1st Stage: Anagen Stage
lasts around 1,000 days
~90% of human hair is in this stage.
period of active growth; follicles divide, deposit
materialwithin the hair.
• 2nd Stage: Catagen Stage
hair grows and changes (grey!)
~ 2% of hair in this stage.
• 3rd Stage: Telogen stage
hair follicle is dormant; hairs easily lost.
~ 10 - 18% of hair in this stage.
28. Human vs. Non Human Hair
Characteristic Human Hair Animal Hair
Pigmentation
pattern
Denser toward the cuticle
Denser toward the medulla.
Often found in solid massses
called ovoid bodies.
Colour
Usually one colour along
the length
Abrupt colour change in
banded patterns.
Medulla Small Larger
Medullary Index
(dia of
medulla/dia of
entire hair)
0.33 or less 0.5 or greater
Cuticle flat, narrow, uneven.
rodents, bats: coronal cuticle
(stack of crowns)
cats,seals: spinous
(like petals)
29.
30. Hair in a Forensic Investigation
• Hair collection: plucking, shaking, scraping, placing
tape.
• Objective: unknown to known evidence (!)
• Most cases: hair is a class evidence.
• Except: DNA profiling.
• Great degree of variation on different parts of the
same head!
• Hair can be:
1) Head hair, 2) eyebrows and eyelashes, 3) beard
and moustache, 4) underarm hair, 5) body hair, and
6) pubic hair.
Needed: About 2 dozen hairs for comparison!
Known sample: include dyed, bleached, grey hair!
31. Hair Analysis.
1) Human or animal hair.
2) Macroscopic Investigation: length,
colour and curliness.
3)Microscopic Investigation: pattern of the
medulla, pigmentation of the cortex, types
of scales on the cuticle, refractive index.
Use: Comparison Microscope.
33. Hair Analysis...cont'd
• Microscopic Investigation:
Phase contrast microscopy: finer details;
better contrast.
Fluorescence Microscope: hair that has
been treated with dyes.
Electron Microscopes: about 50,000 times
magnification.
surface or interior of hair sample.
34. Substances in the hair shaft
Neutron activation Analysis:
• 14 different elements in a 2 cm long hair strand
• antimony, argon, bromine, copper, gold,manganese,
silver etc: identify and quantify.
• Individualisation!!!
• Probability of two people having the same
concentration of all the elements is RARE!
When hair is plucked - blood and tissue; identify blood
type.
DNA Analysis:
• Hair follicle contains mitochondrial DNA.
