Unit 3, Chapter 8 Hairs , Fibers and Paints

1. Unit 3, Chapter 8Hairs, Fibers and Paints

2. Morphology of Hair • Hair grows out of a hair follicle • Shaft: the length of hair that is found above the skin • Shaft is composed of three layers: Cuticle, Cortex and Medulla

3. Cuticle • Scaly structure that covers the exterior of the hair • Scales always point to the tip of the hair • Pattern can be used to identify species • Helps to make the hair resistant to chemical decomposition and to retain its structural features

4. Cortex • Main body of the hair shaft • Made up of spindle-shaped cells that are aligned parallel to the length of the hair • Pigment granules are found in the cortex • Important points of comparison are provided by the color, shape and distribution of the pigment granules

5. Pigment granules found in cortex of hair

6. Medulla • Collection of cells composing the inner canal of the hair • In animals, the medulla is the biggest feature • Medulla can vary within the individual • Three main medulla patterns: Continuous, Interrupted and Fragmented

7. Medulla Patterns

8. Root • Helps to produce hair and continue growth • Shape and size can determine the growth phase of the hair

9. Phases of Growth • Anagen Phase: Initial phase of growth when the follicle is producing hair • Catagen Phase: Transition phase between anagen and telogen • Telogen Phase: Final phase where the hair naturally falls out

10. Pictures of Phase of Growth

11. What can be determined from hair? • Racial Origin • Male or female if tissue adheres to the hair • Whether the hair fell out or was forcibly removed • Type of hair (what part of body it originated in)

12. Collection and Preservation • Must collect reference/standard samples from SAME part of body where the hair originated • 25-50 full length hairs collected for reference sample • Hair can be pulled or clipped at skin level

13. Fibers • Material composing fabrics and garments • Two types: Man-made and Natural

14. Natural Fibers • Derived completely from plant or animal sources • Identified by microscopic examination of color and morphology of fiber • Most prevalent is cotton

15. Microscopic Examination of Cotton Under microscope, the cotton looks like twisted ribbon or collapsed and twisted tubes. These twists are called convolutions.

16. Man-Made Fibers • Fibers created from natural or synthetic polymers • Dates back to 1911 with rayon and 1939 with nylon • Polymers: chains of regular and repeating atoms

17. Microscopic view of polyester Smooth fibers with regular diameter. Diameter generally ranges from 12-25 micrometers. The un-dyed fabric is usually off white and transparent.

18. Comparison and Identification of Fibers • Most important is the ability to trace the origin of the fibers • Only if pieces completely fit together can a definite origin be determined • If cannot fit together, the fibers must be compared side-by-side with standard/reference samples

19. Comparison and Identification of Fibers cont’d • First microscopically compare fibers for diameter and color • Look for other morphological details like striations or pitting • Use Visible light Microspectrophotometer to analyze colors of fibers for comparison

20. Collection and Preservation of Fiber Evidence • Know potential carriers of fiber evidence • Collect and package evidence in separate paper bags • Fold blankets, carpets and rugs to prevent loss of evidence • Cover car seats with polyethylene sheets

21. Examination of Paint • Examine two paint samples to determine same origin • Generally used in burglaries, hit-and-run accidents or vehicle accidents

22. Composition of Paint • Paint is composed of a binder, pigments and additives dissolved in a solvent • Paint is spread onto a surface and dries in a hard film • As it dries, the solvent evaporates leaving behind the binder and pigments suspended in it

23. Automotive Paint Layers • Electrocoat primer: applied to steel body to prevent corrosion, generally gray or black • Primer Surfacer: Completely smoothes out surface. Highly pigmented to minimize difference in color between basecoat and primer

24. Automotive Paint Layers, cont’d • Basecoat: Provides the color and finish of the car. Must be able to resist UV rays, weather and acid rain. • Clearcoat: Un-pigmented layer used to improve gloss and durability of the paint

25. Examination of Paint • Color determination is used to identify paint • Two paint samples would be examined under stereoscopic microscope for color, surface texture and color layer sequence • An increase in the complexity of the layer structure gives a sample greater forensic value

26. Examination of Paint, cont’d • Use pyrolysis gas chromatography to determine paint formulation • IR Spectrophotometry is used to determine composition of paint • Analyze the inorganic pigments in paint using neutron activation analysis, X-ray diffraction and X-ray spectroscopy. • Compare paint make-up to color charts maintained by car manufacturers to determine make and year of car

27. Collection and Preservation of Paint Evidence • Pick up with forceps or scooped up with paper • Use druggist folds or glass vials to contain paint • Collect standard/reference sample when available using clean scalpel or Exacto Knife