L7: HAIR, FIBRES, GLASS AND PAINT EVIDENCE Flashcards
hair is mainly comprised of?
keratin
how much does hair grow per month?
1cm
Hair fibres grow in what pattern?
cyclic growth pattern
whats 1000 days of growth and whats 100 days fo rest?
1000 - anagen
100 - telegen
whats the intermediate period in hair called?
catagen
what percent is anagen?
80-90% anagen
what percent tis telegen?
10-18% telegen
what are naturally shed hairs ?
mainly telegen undamaged hair root
anagen has a _____ root.
damaged
outer shaft of hair is ___
cuticle
main body of hair ____
cortex
core of the fibre is ____
medulla
hair diameter is between?
approximately 40 - 100 mm
what are the key characteristics of hair?
Length, shape, size,
colour, stiffness, curliness
European hair is known as?
caucasoid
features of caucasoid hair are?
- Fine to medium coarseness
- Straight or wavy
- Oval to circular hair shaft
- Even pigmentation (medium – fine)
Asian hair is known as
Mongoloid
features of Mongoloid hair?
- Coarse and straight with large diameter
- Circular cross-section
- Large pigment granules; reddish
African hair is known as?
negroid
features of negroid hair?
Kinks and curls, flattened cross- section
Largest pigmentation granules
Opaque fibre
do hairs have a lot of individualising features?
no
do FBI to hair analyses?
no
what difficult with hair analysis ?
- Variation between hairs from the same source
- Quality (length of hair)
- Time difference
- Experience of forensic examiner
There are ___ natural and synthetic fibres
countless
fibres secondary transfer is ____
fast
where are fibres strong?
along the length
fibres have low?
solubility and elasticity
do fibres have a high or low melting point?
high melting point
How long are animal fibres?
10 – 80 microns
what are natural fibres?
Animal fibres
Veg fibres
Mineral fibres
what are natural animal fibres?
silk
wool
hair
what are natural veg fibres?
linen cotton jute kapok coir
what are mineral fibres?
asbestos
what are synthetic fibres?
organic fibres and inorganic fibres
name organic fibres that are synthetic polymers?
polyethene, polyvinyl derivatives, polyurethane, polyamide, polyester
name organic fibres the are natural polymers?
cellulose, materials, rayon, viscose, modal, rubber
Name inorganic fibres
carbon, ceramic, glass, metal,
what do cotton fibres look like?
irregular “U-shaped” appearance in cross-section
a twisted undulating and irregular appearance along their length
what does wool look like?
More cylindrical appearance with circular/ oval cross-section
Scalar features along the length of the fibre (hair-like)
what do synthetic fibres viscose or triacetate look like?
Appearance of both examples due to manufacture process
Indentations along the length give the fabric an appropriate quality appearance.
whats a good thing about fibre evidence?
strongly classifiable and often individualisation may be possible.
How to find out what type of polymer a fibre is?
Refractive index and birefringence or infrared microscope or raman micro-spectrometry
How to find out the colour of a fibre?
UV-Visible microspectrophotometry
How to find out a dye mix ?
Chromatography
which technique for fibre analysis is destructive?
chromatography
what is glass comprised of?
Silica with sodium carbonate
what additives improve the durability of glass?
limestone
alumino-silicate
natural glass has what colour tint and why?
green because of Fe2O3 from sand
Glass is very ___ and can be _____
classifiable
individualised
what forensic analyses for glass can be done?
• Physical matching of fragments
• Flatness/ curvature, optical properties
and fracture surfaces
• Density of glass
• Refractive index (RI) of fragments
• Elemental analysis of trace elements (metals)
how is paint usually evidence?
chips or scrapings
what is paint made from?
binder
pigment
solvent
what does binder do in paint?
helps paint adhere is surface
what does pigment do in paint?
provides colour and opacity
what does solvent do in paint?
gives liquid properties, dries during use
how thick is paint layer usually?
20mm – 50mm upwards
white and black paint are usually ______
inorganic
pigments are generally ?
insoluble
binders are based on?
oils, gums or resins
forensic analysis of paint involves
Physical matching of fragments
How else can paint be analysed?
Microscopic examination and measurement of layer thickness and
appearance
How to find the chemical composition of paint ?
FTIR or Raman spectroscopy
How to find the colour of paint?
UV-Vis spectroscopy
How to find elemental composition of paint?
X-ray analysis
How can crystalline pigments be analysed?
X-ray powder diffraction
