1. CHAPTER 10
HAIR AND FIBER

2. 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.

3. 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)

4. HAIR STRUCTURE BELOW THE SKIN
                                                                 
Forensic Science Communications
January 2004 – Volume 6 – Number 1
                                                                                                                
Research and Technology a
HAIR STRUCTURE BELOW THE SKIN

5. 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.

6. CUTICLE SCALES: CORONATE
Scales show crown- shaped pattern
Found in small rodents and bats
Coronate pattern NEVER seen in human hair
FREE-TAILED BAT HAIR

7. 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.

8. CUTICLE SCALES: IMBRICATE
The imbricate (brick-like) or flattened scales. Consists of tightly overlapping scales with narrow margins between the scales.
Usually only found in human hair (some animal species).

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. Absent Medulla No discernable medulla visible
Can be found in human hair and animal hair
Human
Human
Silver fox

16. 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).

17. 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

18. Pigment Distribution in 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
Brown Human Hair
Red Human Hair

19. Scale Casts Scale Cast of Human Hair
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

20. Microscope Slide Preparation
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.

22. 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

23. 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

24. 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

27. FIBERS
                      

28. 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

29. Natural Fibers 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

30. Synthetic Fibers
               
More than half of all fibers used in the production of textile materials are man-made.
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 man-made fiber can be manufacturer-specific
                      

31. Acetate Luxurious feel, appearance Wide range of colors
Shrink, moth & mildew resistant

32. Acrylic Soft, warm Wool-like Fiber retains shape Resilient
Quick-drying
Shrink, moth, fade resistant

33. Aramid Great strength Stretch resistant Does not melt
Highly flame-resistant
Fibers maintain shape and structure even at very high temperatures

34. Lyocell Soft, strong absorbent Easily dyed
Fiber can be made into many textures

35. 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

36. 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

37. Polyester

38. Rayon
First manufactured in 1911

39. Spandex

40. 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.

41. 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.

42. 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.

43. 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.