footwear impression evidence-Will Flashcards
latex derived rubber
vulcanised to increase hardness
environmentally friendly
huge range of working temperatures
polyurethane
variable air bubble content for shock absorption
thermo-set
often used as midsole material as foams
thermoplastic rubber
hard wearing
common
PVC
includes chemicals to prevent stickiness at high temperature
chemically resistant, but sticky when warm
Ethyl vinyl acetate
excellent shock absorption
commonly midsole material as foam material
poor wearing characteristics
molding process
completed sole formed in a mold
cut process
sole is cut from pre-made sheeting material
compression molding
solid plymer material placed into the mold
mold closed, compressed and heated
excess materal leaks around the edges-flashing
cycle may take up to 10 mins
injection molding
soling material injected in liquid form into a closed mold
air holes allow efflux of trapped air - characteristic flashing
formed soling sometimes directly attached to uppers at the same time as the molding process
plastic 3D impressions
variable in quality - dependant upon material texture and stability
may contain contaminants which obscure detail
longevity variable
-rain = stability depends upon medium
casting plastic 3D impressions
casting will destroy the impression
life size 1:1 scale allowing a direct comparison
shows very fine detail
dental stone
-produces high detail, high strength
paraffin wax
-marks in snow
-causes immediate melting of impression
bubbles
sulphur
- marks in snow
- causes immediate melting of impression
- fragile
- H&S implications
give 4 examples of smooth non-porous surfaces
floor tiles
glass
gloss painted surfaces
laminate floor
give 2 examples of smooth porous surfaces
untreated wood
emulsion surfaces
enhancement
improves contrast between the medium and the mark
improves outcome of identification
chemical
powders and suspensions
physical lift
- ESLA
- gel lift
alternative light source
chemical enhancement
thiocyanates
- iron in solid residue will react to form red/brown colour
- good for wet origin marks
8-hydroxyquinoline
- reacts with some metallic ions to produce UV fluorescence -Aluminium
- wet or dry origin marks
physical developer
-silver deposited preferentially on waxy materials
iodine
- vapour will cause a yellow/brown colour change in waxy or oily materials
- will subline
bromophenol blue
- turns from yellow to blue above pH 4.6
- good for some dry origin marks
enhancement for marks in blood
leucomalachite green
-colour change to green
luminol/blue star
-production of luminescence visible in darkened area
leuco-crystal violet
-colour change to violet
kastle-meyer
-colour change to pink
acid yello-7
acid black 1
acid violet 17
chemical enhancement for blood
suspected bloodstains first fixed
- commercial blood fix
- sprayed
dyed
- covered in absorbent material
- material covered in dye and left for 30 mins
wash
-dye washed off and dabbed with absorbent material
other enhancement techniques
powder enhancement
vacuum metal deposition
superglue fuming
what does ESLA stand for?
electrostatic lift apparatus
ESLA
designed to lift dry origin dust impressions from a surface
limited use for damp or wet origin marks
best used when a surface medium cannot be removed
ESLA method
film places over mark
device connected to film and also to ground
uses a build up of static charge in the film to lift particles from the mark onto the film surface
ESLA issues
limited success with some types of mark
unless the film is well stored
-continues to attract ambient dust particles
gel lift
gelatine based adhesive surface
a low tack solution for lifting dry/wet impressions
inferior to ESLA for dry impressions
superior to adhesive and can lift from various media
ideal for powdered impression
best used when a surface medium cannot be removed
gel may be coloured to improve mark contrast
name an issue with gel lift
loses tack over time
alternative light sources
crimelites or Quasar
marks may be visible under illumination at appropriate wavelength
simple oblique is most reliable lighting technique
photography
marks and 3D impressions respond well to oblique lighting
shield from ambient lighting
name 3 footwear databases
NFD
Solemate and SICAR
FIT
class characteristics
repeatable characteristics shared by many or all shoes of the same type or class
Shallamach wear
known as feathering
caused by abrasive forces
rubber shaped into wave like formations
similar to friction ridges
very short lived
wear characteristics
short
- wear marks consistent
- some additional wear possible but unlikely
medium
- consistency poor
- additional wear features more likely
- original wear features spread
long
-footwear unlikely to be in circulation
identifying characteristics
random events giving rise to a unique characteristic found on only that shoe
