Chapter 8

Hairs, Fibers, and Paint

I. Hair

A. Morphology of Hair– 1. General Information

a) Hair is an appendage of the skin b) Grows out of the hair follicle c) 3 parts of the entire hair

– i) Root or bulb, embedded in the follicle– ii) Shaft– iii) Tip or end

d) The shaft has 3 layers– i) Cuticle– ii) Cortex– iii) Medulla

I. Hair

– 2. The Cuticle a) Resistant to chemical decomposition b) Retains structural features c) Formed by overlapping scales that point toward the

tip– i) The scales can be used to identify animal species

– 3. The Cortex a) Spindle shaped cells b) Aligned parallel to the length of the hair c) Embedded with pigment for hair color

I. Hair

– 4. The Medulla a) Looks like a canal in the center of the hair b) Larger in animals c) Medullary index measures the diameter of the

medullar relative to the diameter of the hair shaft d) The presence or absence of a medullar varies

– i) Considered continuous, interrupted, fragmented, or absent

e) Human medulla are cylindrical f) Other animals have patterns

I. Hair

– 5. The Root a) Contained within the hair follicle b) Responsible for hair growth c) 3 phases to hair growth

– i) Anogen, can last for 6 years, looks like a flame shape When pulled, the follicular tag is important for DNA analysis

– ii) Catagen phase, lasts 2 to 3 weeks, looks elongated Hair grows at a reduced rate

– iii) Telogen phase, the root looks like a club Can last 2 to 6 months Hair is pushed out of follicle, “shedding”

I. Hair

B. Identifying Hair– 1. General Concepts

a) First step is to determine if hair is human b) Compare hair to other hairs taken from known individuals c) Use a comparison microscope to compare hairs

– i) Determine if hair is dyed or bleached– ii) Hair growth occurs at 1cm per month and time since dying or

bleaching can be estimated (some variations show 4 cm/mo)– iii) Determine morphological abnormalities

d) Considered “class” evidence, can’t positively concluded it came from a particular person

Human hair

Animal hair under polarized light microscope

I. Hair

– 2. Determining Region of Origin a) Easy to do b) Scalp shows little diameter variation c) Pubic hairs are short and curly d) Beard hairs are coarse and triangular, with blunt tips

– 3. Determining Race a) Easy with Caucasian and Negroid

– i) Negroid is kinky with dense, uneven pigments– ii) Negroid hair has cross-sections that are flat or oval– iii) Caucasian hair is straight or wavy with very fine coarse

pigments, evenly distributed– iv) Caucasian hair has cross-sections that are oval to round

I. Hair

– 4. Age and Sex Determination a) Infant to adult yes b) Sex no, still studying

– 5. Determine if Hair was Forcibly Removed a) If the follicular tissue is present, it was pulled b) Data shows, not completely reliable

– 6. Individualizing Human Hair a) Only possible with nuclear DNA (found in the root or

follicular tissue) b) Research is currently looking at mitochondrial DNA

I. Hair

C. Collection of Hair– 1. General Concepts

a) Must have control samples from both the victim and the support

b) Hairs must come from the same region c) Typically collect 50 full-length hairs from the entire

head d) Typically collect 24 hairs from the pubic region e) Must collect the entire length of hair

II. Fibers

A. Types of Fibers– 1. General Concepts

a) Fibers, threads, and pieces of clothing can remain after impact

b) Can become fixed in screens or attached to glass during break-ins

c) Must find the origin of materials left behind d) Must begin with “is the fiber natural or man-made?”

II. Fibers

– 2. Natural Fibers a) Either made from animal or plant b) Most are animal

– i) Include hair coverings ii) ex. wool, mohair, cashmere, camel

– ii) Fur fibers are mink, rabbit, beaver, and yes muskrat c) Most common plant fiber is cotton

– i) Too common for use as evidence, unless dyed– ii) Cotton has a ribbon-like shape

II. Fibers

– 3. Man-made fibers a) Rayon was the First (1911) b) Most listed under generic names (family names)

– i) Polyester- Dacron®, Fortel®, and Kodel® (Terylene® in England)

c) Some are processed out of chemically treated cellulose called regenerated fibers

d) Synthetic fibers include nylon, polyester, and acrylics– i) Created from polymers

Major Generic Fibers and Tradenames

Characteristics

Acetate Luxurious feel and appearance; wide range of colors and lusters; etc.

Acrylic Soft and warm, wool-like, lightweight; retains shape; etc.

Aramid No melting point; highly flame-resistant; etc.

Modacrylic

SEF

Soft, resilient, abrasion- and flame-resistant; quick-drying; etc.

Nylon Exceptionally strong, supple, abrasion-resistant; lustrous; etc.

Olefin Unique wicking propertied that make it very comfortable. Abrasion resistant; quick-drying; etc.

Major Generic Fibers and Tradenames

Characteristics

Polyester Strong, resistant to stretching and shrinking; resistant to most chemicals; etc.

PBI

PBF

Highly flame-resistant. Outstanding comfort factor combines with thermal and chemical stability properties. Etc.

Rayon Highly absorbent; soft and comfortable; etc.

Spandex Can be stretched 500 percent without breaking; can be stretched repeatedly and recover original length; etc.

Sulfar High-performance fibers with excellent resistance to harsh chemicals and high temperatures. Excellent strength retention in adverse environments; etc.

Vinyon Softens at low temperature; high resistance to chemicals; etc.-

II. Fibers

– 4. The Polymer a) Basic substance of all synthetic fibers b) Made up of molecules connected together in chains

creating macromolecules c) Monomers are the single molecules within a chain

III. Identification of Man-made Fibers

A. General Concepts– 1. Must trace the origin of the fiber

a) Look at color microscopically b) Look at diameter microscopically c) Also consider lengthwise striation, pitting with delustering

compounds and cross-section shape

– 2. Color matches are not easy a) Microscopic investigation reveals base color differences b) Dye composition becomes the “key” to identification

– i) Use chromatagraphic separation to determine dye composition

III. Identification of Man-made Fibers

– 3. Fibers must match in chemical composition a) Use double refraction or birefringence properties for

classification b) Light polarization frequencies can determine class of

fiber– i) Use infra-red light and spectrophotometry– ii) Absorbencies can be matched

IV. Collection of Fiber Evidence

A. General Information– 1. Actually look for fiber “carriers”

a) Articles of clothing b) Samples of carpet fibers and rug fibers c) Collection of bedding materials d) Car seats are covered by polyethylene sheets e) Knife blades are covered f) Use adhesive tape to “lift” fibers off of a body

– 2. Examine other crime scene debris a) Time consuming and tedious

V. Examination of Paint

A. General Information– 1. Many surfaces are painted– 2. One of the most prevalent types of physical

evidence– 3. Most often hit-n-run and burglary cases– 4. required to compare two or more paints– 5. Paint is a mixture of inorganic and organic

compounds (binders) and pigments

V. Examination of Paint

B. Automotive Paint– 1. First layer is the Electrocoat Primer

a. has resins to adhere to metal, provides corrosion resistance

– 2. Second layer is the Primer Surfacer a. also an anti-corrosive foundation

– 3. Third layer is the Basecoat a. called the colorcoat b. provides color and aesthetics for color finish c. resistant to UV light

V. Examination of Paint

B. (cont)– 4. Fourth (last) layer is the Clearcoat

a. improves gloss

C. Identification of Paint– 1. Pyrolysis gas chromatography is used to

determine paint formulations a. as small as 20 micorgram sample can be tested b. heat decomposes the paint into separate polymers

– i. creates a paint polygram

V. Examination of Paint

C. (cont)– 2. Inorganic Compounds are identified by several

techniques a. emission spectroscopy b. neutron activation analysis c. X-ray diffraction d. X-ray spectroscopy

Emission Spectroscopy

Neutron Activation Analysis

X-ray Diffraction

X-ray Spectroscopy