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Year 10 Forensic Science Hair and Fibre analysis
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Forensics of Fibres
What is a fibre?
• A fibre is the smallest unit of a textile material.
• Fibres can occur naturally or be man-made.
• A fibre can be spun with other fibers that can be woven or knitted to form a fabric.
• The type and length of fibre affects how easily it transfers from person to person.
Fibre Evidence
• Fibres are gathered at a crime scene with tweezers, tape, or a vacuum.
• They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets.
• For analysis, it is first decided whether it is natural, man made, or a mix of both.
Cotton from a plant
Silk from the silk worm
Wool from
sheep
Linen from the
flax plant
Hair fibres from rabbits
& goats
Plant fibres made from the
organic compound cellulose
Flax
Wool Silk
Cotton
Cashmere
Animal fibres made from the
organic compound
protein
Angora
All fibres come in different lengths.
Some are short some are long!
Flax
Wool
Cotton
Angora
25cm-150cm1cm-6cm
7.5cm-12cm
6cm-10cm
6cm-20cm Cashmere
They are all called
STAPLE fibres
Silk is the EXCEPTION because it
is very long! Up to 1km which is what we
call endless.
They are all called
FILAMENT fibres
Worm
Cocoon
Fibre
Fabric
Natural Fibres
Cotton fibres are the plant fibres most
commonly used in textile materials.
Cotton fibres
Other plant fibres
• Flax (linen), ramie, sisal, jute, hemp, kapok, and coir.
• The identification of less common plant fibres at a crime scene or on the clothing of a suspect or victim would have increased significance.
Flax fibers viewed with
polarized light
Animal Fibre: Wool• Wool is the most frequently
used.
• The most common wool fibres originate from sheep.
Wool fibres
Man-Made Fibres
• More than half of all fibers used in clothes are man-made.
• Polyester and nylon fibres are the most common man-made fibers, followed by acrylics, rayons, and acetates.
Cross section of man-made fibers
Why are fibres important?
• The number fabrics produced with any one fibre type and colour is extremely small.
• The likelihood of two or more manufacturers exactly duplicating the textile is extremely small.
Fibre Number
• The number of fibers on the clothing of a victim identified as matching the clothing of a suspect is important in determining actual contact.
• The greater the number of fibres, the more likely that contact actually occurred between these individuals
Fibre Evidence
• The problem with fibre evidence is that fibres are not unique.
• Unlike fingerprints or DNA, they cannot pinpoint an offender in any definitive manner.
• There must be other factors involved, such as evidence that the fibres can corroborate or something unique to the fibers that set them apart.
Hairs
Naturally shed has a clubbed shaped end
Stretched
If there is skin attached DNA can be extracted
Cuticle• The cuticle of a hair is the
thin, clear layer around the shaft.
• It consists of scales of hard protein that varies between animal species.
• The patterns are:– Coronal, or “crown – like.”
typical of rodents. – Spinous, or “petal – like.”
Common in cats, seals, and minks.
– Imbricate, or “flattened.” Humans.
Coronal
Spinous
Imbricate
Cuticle
Photomicrograph of a mink hair
possessing a Spinous cuticle.
Photomicrograph of a bat hair possessing a
Coronal cuticle.
Photomicrograph of a human hair possessing an Imbricate
cuticle.
Medulla
Photomicrograph of a human hair with no
medulla.
Photomicrograph of a hair with trace
medulla.
Photomicrograph of a hair with a clear,
continuous medulla.
The medulla is a central core of cells that runs through the center of the cortex.
Types of human hair
Photomicrograph of an African Head Hair
– Curly, wavy or coiled
– Large pigment granules that clump
Photomicrograph of an Asian Head Hair– Coarse straight– Thick– Large pigment
granules– Reddish
Photomicrograph of a Caucasian Hair
•Fine to medium•Straight or wavy•Blonde, brown, black•Even pigmentation
Race and AgeEvidence From Hair
Hair can be examined to find out:•Race•DNA and Sex •Age (sometimes)•Hair colour (natural or dyed)•Evidence of a struggle
AGE Elderly
Pigment loss FinerDiameter of hairs varies more
Treated hairDyes or rinses are identified using a microscope By measuring the length of the untreated part from the root, the time of treatment can be guessed Direct, side-by-side comparison of the colour of suspect’s hair and the sample
Body hair
Head Hair
Beard Hair
Pubic Hair
Practical
• Part A• Use the microscopes to look at the samples of fibres and animal hair. • Draw a labelled diagram of what you see. (Use your notes as a guide)• Can you identify which are natural or man-made fibres or animal hair?
• Part B• Look at your hair under the microscope.• Do you dye/straighten your hair? Do you sunbathe a lot? If so you
should be able to see the damage you are doing to your hair.• Compare with your friends.
Damaged