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