jimtrue.com : school : CJT2141 : 08: Hair, Fibers & Paint
Posted by Jim True on February 26, 2003 7:00 AM. Last Updated October 22, 2006 9:23 PM
Disclaimer for all material noted here is at the bottom of this web page.
Three basic types (Hair, Fibers, Paint) (Polymers)
HAIR
- Trace evidence examiner goes into a court room, with a pencil (this is what a hair looks like, eraser is the root, point of the pencil, outer covering (cuticle - scale structure)
Wood, middle portion, cortex in the hair (not quite in the center)
Lead, medulla
a. Cuticle, scales
b. Cortex
c. Medulla
Pre-DNA, could not distinguish between a shadow of a doubt that this hair came from the person (unless there was a fracture match).
Root material, can do DNA analysis. Otherwise, we can grind up the hair and do Mitochondrial DNA.
Hair is a waste product; a way for things to exit (drugs); can also come out through the hair follicles. Heavy metals (arsenic). Can tell it was in the system, but not WHEN it was in your system.
Inside the cortex or medulla.
Different stages of growth in the hair (p.193) anagen, catagen, telogen (know these).
Microcopically when looking at hair, can determine:
1. Species (Cuticle and Medulla) (p.192) Shape and dispersion of the medulla, also on cuticle can determine the scale structure. Roll the hair in a casting material (polymer film) gives good imprint of the scale structure.
Cuticle & Medulla to determine what kind of animal you might be looking at.
2. Body location of the hair
Hair serves different purposes, hair on head (waste products), armpits or pubic region, protection (course & curly/kinky). Dark more dense cortex, ends are very tapered, as they are usually not cut.
Eyebrow & moustache and beard, heavier.
3. Racial origin - caucasian, oriental, african-american/negroid:
a. Color and pigmentation shown in Cortex, dark medulla
b. Oriental - very round, pigmentation VERY dark
c. Negroid - flat, like a ribbon, dark cortex but medulla still visible.
4. Age & Sex: age may be able to tell, can determine if hair was forcibly removed.
Class evidence
NEXT LAB ASSIGNMENT - collect 5 different hair samples: (Due 4/2) 30-50 Hairs
1. Head (self) (at least 15 with root; others only a few have to have root).
2. Other Body region, self
3. Animal (brush or stroke the animal) (except the animal)
4, 5. Whatever
FBI Protocols say 30-50 hairs (at least 50% must have root material).
Piece of white paper (pharmacists fold)
Label: Date, What's In the Envelope, and Who the victim is
In thirds, in thirds again, one fold and insert in tube.
After Exam is done, we will examine the hairs with microscopes.
a. Representative sample (all areas of the head).
FIBERS
2 basic types of fibers
1. Natural: cotton (most common), Wool, Silk, Hemp (made for Marine rope)
Cotton, twisted fiber (may be able to test the die)
2. Man-Made: Polyester, Nylon, Rayon, Spandex, Acrylic
Acetate (man-made recycled cellulose)
Kevlar (teflon)
Polymers - many molecules put together
Look at fibers under the microscope (also use polarized light microscope); use because of the monomers in the fibers to determine what kind of material we're dealing with. Composition and bi-refrigence.
Microspectrophotometer - To determine Type FTIR, then go to the Microspectrophotometer and determine the dye.
Use Stereomicroscope to use tweezers to separate out like fibers.
Tape lift on clear acetates.
Evidence collection of Fibers: by tape lift, vacuumings, sweepings, screen. (p. 74, chapter 3, Read article about Fiber evidence - Wayne Williams).
PAINT
a. Automotive (most common)
b. Architectural
c. Marine (very rarely occur)
Coatings
- Solvent (spreadable)
- Binder (carrys the pigment)
- Pigment (color)
Automotive - electrostatic primer, primer, basecoat, clearcoat (4 layers); after wreck, another primer, basecoat and clearcoat. Sometimes lucky, fracture match for individual evidence, usually class evidence.
Pyrolisis Gas Chromatography - take the fragment, melt the whole fragment and get a resultant gas chromatograph. Vaporize the whole chip. Can also run them through a MS.
FTIR - look at each layer, FTIR microscope, chemical makeup will be different for each layers.
Microspectrophotometer - color
Pyrolysis - destroy the paint chip
Spectrophotometry - does not destroy the paint chip.
Make sure you understand 8.
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