Hairs, Fibers, and Paint

Hairs, Fibers, and PaintChapter 13

Hair• Hair morphology (structure)

is a class characteristic, not an individual characteristic

• Hair evidence can indicate physical/violent contact

• Retains structure for a long time

• Analyze color & structure first

• DNA typing can be used later for identification ▫ if follicle cells are found▫ if mitochondrial DNA is used

• Basic Morphology▫ Root bulb in hair follicle▫ Long shaft with 3 layers:

cuticle, cortex, and medulla▫ Tip end

Hair Morphology—Cuticle & Cortex• Cuticle

▫ Protective outer layer on hair

▫ Mostly keratin protein▫ Scale pattern distinguishes

different animal hairs▫ Scales are composed of

hardened dead cells• Cortex

▫ main body of hair shaft▫ spindle-shaped cortical

cells▫ contains pigment granules

that give hair color▫ compare color, shape, and

distribution of granules

Hair morphology—Medulla• Medulla

▫ Cells down the center of hair

▫ Look like central canal▫ Can be continuous,

interrupted, fragmented, or absent

▫ Identify hair type and species by pattern

• Medullary index▫ Calculate ratio of diameter

of medulla to diameter of hair

▫ Distinguish human hairs (index < 1/3) from animal hairs

Hair growth in the root• Anagen phase

▫ Initial growth phase where the hair follicle produces hair

▫ May take up to 6 years• Catagen phase

▫ 2-3 week transition stage▫ Growth slows, root shrinks

• Telogen phase▫ Hair has stopped growing

and slowly falls out naturally▫ May take 2-6 months

• Pulled hairs (anagen phase) have follicular tag which contains DNA for analysis

Distinguishing Human and Animal Hair• Be aware of morphological

differences ▫ within individuals/species▫ between

individuals/species• Compare to reference

samples using a microscope

• Check:▫ Cuticle scale structure▫ Medullary index (<1/3)▫ Medulla pattern or shape

Matching human hair from crime scene• Head or pubic hair

recovered from crime scene must be matched to reference sample taken from individual

• Comparison microscope: match color, length, diameter, medulla pattern, color intensity and pigment distribution in cortex

• Fungal, bacterial, or insect infections can cause unusual features

• Not foolproof – 11% false positive rate!

Identifying types of hair• Variations in color, texture

and patterns within types of hair for one individual

• Scalp hairs: uniform diameter, uniform pigment distribution

• Pubic hairs: short, curly, continuous medullae, wide diameter variations

• Beard hairs: coarse, triangular, blunt tips from shaving

Racial Identity from Hair• Negroid Hair

▫ Usually coarse and tightly curled

▫ Flat to oval cross-section ▫ Dense, unevenly

distributed pigment• Caucasian Hair

▫ straight or wavy▫ fine to coarse▫ pigments are more evenly

distributed▫ Circular to oval cross-

section

Determining Age and Gender from hair• Infant hairs are fine and

short with fine pigmentation

• Nothing else about age can be determined from hair

• Presence of dye/bleach might help determine gender

• Analysis of DNA from hair follicle can be used for gender analysis

Definite Identity• Hair alone cannot be used

for definitive identity without DNA analysis of follicle cells

• Central Park Jogger case (1989-2002)

• http://www.youtube.com/watch?v=fGc4PaLB-ek

Hair collection and preservation• Get many standard

reference samples from victims and suspects from various body locations

• Can be a lot of variation in any one region; so many reference hairs from that area are necessary

• Usually 50 scalp hairs and 24 pubic hairs are collected for comparison

Fiber Analysis• Fibers from fabric or

garments are collected from crime scene▫ Crimes with physical

contact▫ Assaults, homicides, sex

crimes▫ Hit-and-run▫ Breaking and entering

• Identify type and source• Compare to reference

samples collected from suspects’ belongings

Natural Fibers• Wholly derived from

animal or plant sources• Most common is animal

hair▫ wool, furs, mohair,

cashmere, etc.▫ Perform hair analysis

with microscope• Cotton is the most

prevalent plant fiber• Analyze microscopically

for color and morphological characteristics

Manufactured Fibers

• Garment fibers derived from natural or synthetic polymers like nylon and rayon

• Regenerated fibers▫ Raw material is natural: cotton or wood pulp▫ Cellulose is extracted and chemically

treated or dissolved▫ Forced through small holes of a

spinning jet▫ Include rayon, acetate, triacetate

• Synthetic fibers▫ made from synthetic chemicals▫ Include nylon, polyester, spandex, and

acrylic • Polymer

▫ Very long, repeating macromolecule▫ Synthetic polymers (polyester, etc)▫ Natural polymers such as cellulose,

starch, and keratin

Identifying Manufactured Fibers• First step: microscopic analysis

for color, diameter, shape, and patterns▫ If they match, do further analysis

• Dye composition▫ Visible-light

microspectrophotometer Mount fibers on microscope slide Uses spectral patterns to

compare fiber colors Works even with a tiny sample

▫ Chromatograph separation Extract dyes from fiber Put spot of dye on thin-layer

chromatography plate Colors separate and can be

compared

Chemical Composition of Fibers• Fibers that match

morphological and color characteristics are compared to see if same chemicals are present

• Verifies that a set of fibers come from same class:

Which type of nylon or acrylic?• Works on very small

sample

Birefringence• Crystalline manufactured

fibers cause double refraction

• A beam of light shifts when it travels through the material

• Different materials have different indexes of refraction

• Immerse fiber in similar liquid and see it disappear

• Shine polarized light through fiber, measure birefringence

• Does not harm fiber

Infrared Absorption• Different manufactured

polymers absorb infrared light in different characteristic patterns

• Done with spectrophotometer connected to microscope = microspectrophotometer

• Identify the generic class (nylon, acrylic, etc) and sometimes more specific type

Fiber Evidence Significance• Can be used to determine group characteristics that

can be matched to reference samples• Factories produce lots of identical clothing with

identical fibers• More powerful if two or more fibers match• Can be used as supporting evidence• Not strong individual evidence

• Fiber video:• youtube.com/watch?v-BjLHW7qQEIO

Paint Analysis• Electrocoat Primer—first layer

of auto paint; electroplated primer for corrosion resistance; black to gray

• Primer Surfacer—On top of electrocoat; corrosion resistance; hides any seams or imperfections

• Basecoat—colorcoat provides color and finish; resists weather, UV radiation; metals are added to add luster to paint

• Clearcoat—unpigmented to improve gloss, durability and appearance

Microscopic Analysis of Paint• Color and appearance of

evidence chips are compared to known samples under a microscope

• Most important and most common analysis tool for paint

Chemical Analysis of Paint• Pyrolysis Gas Chromatography

is used to separate and to isolate the chemical components of paint

• Since paint components cannot be dissolved into a solvent for gas chromatography.

• So, paint samples are heated very high (pyrolyzed) so that they decompose into gaseous products that can be separated via chromatography.

• Paint pyrograms show chemical make up of binder

Spectroscopy• Line spectrum of each

element is different• Can be used to identify

elements in a paint sample• Plasma Emission

Spectrometry is replacing other traditional means; uses a hot plasma torch to see response to light energy

Paint Data Query• Paint database for

automobile paint comparisons

• Can match evidence samples to year and make of car

• Then, only need reference samples from that year and model