1. Chapter 8 Hair, Fibers, And Paint

2. Introduction HAIR FIBERS AND PAINT
Physical evidence in a variety of crimes
Not yet possible to individualize human hair to any single head or body through morphology
Still has value as physical evidence
HAIR FIBERS AND PAINT

3. Introduction HAIR FIBERS AND PAINT
Properly collected and submitted to the laboratory
Accompanied by adequate number of standard or reference samples
Provides strong corroborative evidence for placing individual at crime scene
HAIR FIBERS AND PAINT

4. Fiber Evidence

5. Types of Fibers: Natural Fibers
Derived in whole from animal or plant sources
Wool
Mohair
Cashmere
Furs
Cotton
Animal fibers: hair
Cotton: most prevalent
HAIR FIBERS AND PAINT

6. Natural Polymers
Figure 8–10  Starch and cellulose are natural carbohydrate polymers consisting of a large number of repeating units or monomers.

7. Types of Fibers: Man-made Fibers
Manufactured
Regenerated fibers
Manufactured from natural raw materials
Rayon, acetate, and triacetate
Synthetic fibers
Produced solely from synthetic chemicals
Nylons, polyesters, and acrylics
HAIR FIBERS AND PAINT

8. Types of Fibers: Polymers
Macromolecules
Synthetic fibers
Repeating units known as monomers
HAIR FIBERS AND PAINT
Figure 8–9  The chain-link model of a segment of a polymer molecule. The actual molecule may contain as many as several million monomer units or links.

9. Fiber Evidence Identify the origin of the fiber
Or at least narrow the possibilities to a limited number of sources
Fabrics that can be exactly fitted together at their torn edges = fabrics were of common origin
HAIR FIBERS AND PAINT

10. Fiber Evidence
Microscopic comparisons between questioned and standard/reference fibers
color and diameter characteristics
comparison microscope
HAIR FIBERS AND PAINT

11. Fiber Evidence
HAIR FIBERS AND PAINT

12. Acrylic

13. Polyester

14. Cotton

15. Wool

16. Fiber Evidence Other morphological features for comparing fibers are
Lengthwise striations on surface of fiber
Presence of delustering particles that reduce shine
Cross-sectional shape of the fiber
HAIR FIBERS AND PAINT

17. Fiber Evidence Compositional differences
Dyes that were applied to fibers during the manufacturing process
Microspectrophotometer
Chromatography of pigment
Chemical composition of fibers
Birefringence: crystalline property of fiber
HAIR FIBERS AND PAINT

18. Burn Test
HAIR FIBERS AND PAINT

19. Burn Test
HAIR FIBERS AND PAINT

20. Burn Test
HAIR FIBERS AND PAINT

21. Methods For Fiber Comparison
Visible light microspectrophotometer
Compare colors of fibers through spectral patterns.
Chromatographic separation: dye composition
Generic class of fibers
Infrared spectrophotometry
Polarizing microscope: characteristic index of refraction
HAIR FIBERS AND PAINT

22. Collection and Preservation
Investigator’s task
Look for minute strands of fibers
Identify and preserve potential “carriers” of fiber evidence
Relevant articles of clothing
Packaged carefully in separate paper bags
If necessary to remove a fiber from an object
Use clean forceps
Place in a small sheet of paper
Fold and label the paper
Place the paper packet inside another container
HAIR FIBERS AND PAINT

23. FBI Hair Paper

24. Summary