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Analytical Techniques In Forensic Science > Analytical Techniques For Trace Evidence > Flashcards

Analytical Techniques For Trace Evidence Flashcards

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1
Q

What kind of cases might require chemical analysis of glass evidence ?

A

-burglary
-car accidents
-assault

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2
Q

Why is the location of glass relevant ?

A

The location of glass is dependent on what is analysed/ evidential value

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3
Q

How is glass recovered from clothing/ shoes ?

A

-seal pockets/ trousers turn ups
-recover hairs/ fibres by lightly taping
-shake item/brush onto brown paper
-check pockets and turnups last

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4
Q

How is glass and fibres recovered from hair ?

A

Combing

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5
Q

How is glass and fibres taken from other surfaces ?

A

Tweezers

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6
Q

What controls are taken from glass recovery ?

A

-blank sample
-reference sample at crime scene is taken from the frame not from the glass on the floor

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7
Q

When would a forensic scientist analysis glass ?

A

-SOCOs will recover glass or size items with glass on it.
-volume crimes- don’t usually examine glass because a suspect is not located quickly enough
-serious crimes-more likely to analyse glass evidence

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8
Q

What is the evidential value of glass in hair combing ?

A

Highest evidential value

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9
Q

What is the evidential value of glass embedded in soles of footwear ?

A

Lowest evidential value

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10
Q

What is float glass ?

A

-very common (windows)
-smashes into mixed sized fragments with sharp edges
-edges can tell us how fresh the smash was

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11
Q

What is tampered glass ?

A

-common (motor vehicles)
-safety glass
-hard to smash
-forms cubes
-tends to clump together
-edges indicate thermal or physical stress and impact

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12
Q

What is laminated glass ?

A

-2+ panes joined by plastic (PVB bond)
-common (windscreen glass)
-less common (bullet resistant, smart glass)
-sticks together
-safety

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13
Q

What is wired glass ?

A

-less common (fire doors)
-mesh through the pane
-tends to be indoors (rusting)

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14
Q

How does glass smash ?

A

Backwards fragmentation

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15
Q

What is a radial crack ?

A

Radiate in Amy directions away from the point of fracture

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16
Q

What is a concentric crack ?

A

Imperfect circle around the point of fracture

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17
Q

What are the different types of analysis for glass ?

A

-chemical
-refractive index
-mechanical fit

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18
Q

What is chemical analysis for glass ?

A

Identifies oxides in colouring and impurities in constituent parts used in manufacture

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19
Q

What is refractive index analysis for glass ?

A

Light refraction as it passes through glass, measured in heated oil. The RI changes as it’s heated, and when the sample disappears the RI value is known

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20
Q

What is mechanical fit for glass ?

A

Large fragments might stick together
Conchoidal stress marks

21
Q

What equipment is used to analyse glass ?

A

-GRIM
-X-Ray fluorescence
-Scanning electron microscope
-surface examination
-annealing

22
Q

What is GRIM analysis ?

A

Measures optical properties of glass
-tiny fragments <0.5 mm

23
Q

What is X-Ray fluorescence analysis ?

A

Elemental composition of glass

24
Q

What kind of cases might require chemical analysis of fibre evidence ?

A

-hit and run
-car crash/ accident
-sexual assault
-burglary

25
Q

Where might you find samples of fibres ?

A

Everywhere

26
Q

How are fibres recovered from clothing ?

A

-tape lifting
-plastic tweezers
-vacuuming
-shaking
-brushing
-place in paper bag

27
Q

What are the different types of fibres ?

A

-natural and synthetic/man-made
-further classified: animal, vegetal or mineral

28
Q

What are examples of natural fibres ?

A

Vegetable: cotton, hemp
Mineral: asbestos
Animal: wool, silk

29
Q

What are examples of man made fibres ?

A

Natural polymer: acetate, viscose
Synthetic: polyester
Inorganic: carbon, glass

30
Q

What does cotton look like etc ?

A
  • strong, tough and flexible
    -absorbs moisture
    -doesn’t retain shape
    -length and degree of twist differed based on type of cotton
    -if ignited burns with steady flame
    -smells like burning leaves
31
Q

What does linen look like etc ?

A

-individual plant fibres are longer
-takes longer to ignite
-if burning can be extinguished by blowing like a candle

32
Q

What does silk look like etc ?

A

-burns easily but not as steadily as Cotten/ linen
-smells like burning hair
-not as easy to extinguish

33
Q

What does wool look like etc ?

A

-from sheep’s, goat
-individual fibres are shorter than silk
-diameter of fibres is relevant
0fineness indicates usage-clothing vs carpet
-harder to ignite with a steady flame but difficult to keep burning
-smells like burnt hair

34
Q

What does acrylic look like etc ?

A

-made from natural gas and petroleum
-retains shape; wool like
-resistant to moths, sunlight and oil
-burns readily due to contents and air filled pockets
-will ignite fast and will continue burning until extinguished
-smells acrid or harsh

35
Q

What does nylon look like etc ?

A

-made from petroleum
-exceptionally strong and abrasion resistant
-damage resistant to oils and many chemical
-low in moisture absorbency
-melts and burns fast if flame remains on melted fabric
-smells like burning plastic

36
Q

What does polyester look like etc ?

A

-made from coal, air, water and petroleum products
-strong-resistant to stretching and shrinking
-resistant to most chemicals
-quick drying
-wrinkle resistant
-melts and burns at the same time
-dripping ash Bon’s with any surface it encounters
-smells ‘sweetish’

37
Q

What do synthetic fibres tell us about?

A

-blends- two or more fibres
-should take characteristics of each fibre
-burning test can be used but fabric content will be an assumption

38
Q

What identification techniques are used for fibres ?

A

-primary examination
-chemical examination

39
Q

What is the primary examination for fibres ?

A

-visual - colour, location, amount
-microscope - comparison
-birefringence

40
Q

What is the chemical examination for fibres ?

A

Involves the extraction of dye and identifying and characterising the chemical structure

41
Q

What equipment is used to analyse fibres ?

A

-SEM
-Raman spectroscopy
-IR spectroscopy
-UV vis spectroscopy

42
Q

What kind of cases might require a chemical analysis of paint evidence ?

A

-hit and run
-car accident/ crash
-break in

43
Q

Why don’t SOCOs use tape to lift paint samples ?

A

Paint has multiple layers so the tape might remove a layer

44
Q

How is paint recovered from clothing ?

A

-plastic tweezers
-shaking
-brushing
-place in paper bag

45
Q

How is paint removed from other surfaces ?

A

-tweezers
-sharp edged knife

46
Q

What is the chemical examination of paint ?

A

Side by side comparison under Low power stereo microscope for colour, surface texture and colour layer sequence

47
Q

What is colour layer sequence ?

A

-trying to match the layer number and sequence of colour as it the sample will be made up of diffferent layers (base coat, binder, primer and topcoat )

48
Q

What is the second part of the chemical analysis of paint samples ?

A

Analysing individual layers

Analytical Techniques In Forensic Science (5 decks)

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