fibre and hair analysis
DESCRIPTION
Year 10 Forensic Science Hair and Fibre analysisTRANSCRIPT
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Forensics of Fibres
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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.
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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.
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Cotton from a plant
Silk from the silk worm
Wool from
sheep
Linen from the
flax plant
Hair fibres from rabbits
& goats
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Plant fibres made from the
organic compound cellulose
Flax
Wool Silk
Cotton
Cashmere
Animal fibres made from the
organic compound
protein
Angora
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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
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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
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Natural Fibres
Cotton fibres are the plant fibres most
commonly used in textile materials.
Cotton fibres
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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
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Animal Fibre: Wool• Wool is the most frequently
used.
• The most common wool fibres originate from sheep.
Wool fibres
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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
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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.
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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
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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.
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Hairs
Naturally shed has a clubbed shaped end
Stretched
If there is skin attached DNA can be extracted
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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
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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.
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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.
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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
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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
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Body hair
Head Hair
Beard Hair
Pubic Hair
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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