Fibres Flashcards
Where can fibres transfer to
- Contact between persons = transfer from one individual to another
- Left at a scene of a crime
- Left on a weapon or car
- Secondary transfer
- Tertiary transfer
Give an example of a crime where person to person fibre transfer can occur
Sexual Assault
GBH
Manslaughter
Murder
Give an example of a where person to scene fibre transfer can occur
Point of entry
Deceased
property
What are the 2 broad groups fibres can be classified into
Natural and Man-made
What are the most common natural fibres and where do they come from
Animal:
- Wool
- Cashmere
- Animal skin
Plant:
- Cotton
- Hemp
Define Man-made/synthetic fibres
Produced solely from synthetic chemicals.
Synthesised long-chained molecules
(polymers).
What are common synthetic fibres
Nylon
Polyester
Acrylics
Describe cotton fibres
Very Fine
Regular
Twisted Ribbon or collapsed twisted tube shape
Describe wool fibres
Thick fibre
Regular
Distinctive scale pattern
How can you differentiate between natural and synthetic fibres
Synthetic fibres are all created to look the same
Delusterant - Titanium oxide particles added
during manufacturing to reduce
shine.
Seen as particles within the fibre.
Striations along fibre length
Dye pigment
Cross-section - Created by manufacturing process
When will transferred fibres begin to be lost from an item
Immediately after contact therefore the items will need to be recovered ASAP
What factors effect the rate of loss of fibres
- Degree of activity after fibre transfer
- Packaging
- Location on the person of contact e.g. exposed areas = increase chance of loss
- Washing
- Clothing worn over areas of contact
- Physical properties e.g. burning
Describe tape searching (fibres)
- Fabric garments are taped using adhesive clear tape to recover extraneous fibres anywhere on the surface of the item.
- Amount of tape depends on the garment and how it readily sheds
- systematic approach is used
- Looked at under a LPM (light polarizing microscope)
- The relevant fibres are circled with permanent pen
Name the ways fibres can be analysed
- Comparison Microscopy
- TLC - Thin layer chromatography
- FT-IR
- MSP - Microspectrophotometry
- PLM - Polarized light microscope
What information can you gain from analysing fibres
Type Colour Number of fibres Presence of multiple fibres What textile the fibre came from Uniqueness of the fibre
Describe Comparison Microscopy (fibres)
-Compare control fibres with unknown fibres
recovered from tapes side-by-side under the
comparator.
-Can compare under different wavelengths of light:
white (visible)
blue
UV
Describe Thin Layer Chromatography (TLC) (fibres)
-The analysis of fibre dyes to determine their colour
comparison.
-At this stage can exclude some fibres as matches.
-Technique incorporates a solid stationary phase
and a moving liquid phase to effect the separation
of dyes.
-Solid phase – thin layer plate coated in silica gel.
-Moving liquid phase – suitable solvent
-Rf values are calculated after liquid moves past 10cm
How are Rf values calculated
Rf value = Distance travelled by component/Distance travelled by moving phase
How are Refractive Indexes measured (RI)
RI = Velocity of light through vacuum/ Velocity of light through medium
Describe Microspectrophotometry (fibres)
- The instrumental analysis of the colour characteristics of a fibre.
- Microscope combined with a spectrophotometer.
- Obtains an electromagnetic spectrum of any dyes or pigments present.
- Can be compared to that of control fibres.
Describe Fourier Transform Infra-red Spectroscopy (FT-IR) (fibres)
- The instrumental analysis of the chemical composition of the fibre itself (man-made fibres only).
- Concerned with the energy changes involved in the stretching and bending of covalent bonds in molecules.
- Each peak corresponds to a specific chemical bond
- Used as a qualitive tool only
