Lecture 17: Advanced evidence types

Question 1

Glitter

Answer 1

• Not the same as shimmer!
• Synthetic multilayered particles - plastic (polyethylene terephthalate/PBT/PMMA) or aluminium, or a hybrid
• Cut from rolled sheets – tend to be hexagonal, square or rectangular, can be custom shaped
• Can be layers of plastics or layers dispersed with aluminum or just aluminium itself
• Shapes are more cost effective to produce
• Custom shapes will be larger as theyre meant to be seen.
• Can be found in decorative cosmetics, sunscreens and various personal care products
• Also in gel pens, temporary tattoos, glues, paints, toy slime, on glass, or loose (no vehicle)
• No vehicle means on it’s own.
• Glitter encrusted garments or woven into fabrics, threads, strands and yarns.

Question 2

Glitter vs shimmer

Answer 2

• Shimmer is predominantly mica based (muscovite)
• Used on its own → pearlescent effects
• Used as a substrate then coated with various metal oxide layers – TiO2, Fe2O3, Fe3O4, BiOCl, SnO2, carmine, ferric ferrocyanide, chromium oxide → interference effects
• Glitter is synthetic; mica based shimmer is natural
• Whether mica is used alone, or coated with metal oxides, it never contains plastic; glitter almost always does (see later slides though!)
• Glitter (of a given type) will have identically shaped and sized particles; shimmer particles are irregularly and randomly shaped and sized.

Question 3

Recovery considerations for glitter

Answer 3

• Unlike cosmetic traces, glitter (and shimmer) should be analysed as multilayered paint flakes
• Use a high intensity light source!
• Must not be lifted with J-Lar or acetate – post-its
• Glass or plastic vial is the best option, then bag
• Embedded particles must not be removed at scene
• Don’t refrigerate or freeze
• Use a high intensity light source to help recover glitter.
• Multilayerd particles are prone to delayering
• Water could delaminate the layers

Question 4

Analytical workflow for glitter

Answer 4

• Gross examination, recovery and collection
• Preliminary evaluation of physical characteristics – micrometer gauge or microscopically
• Physical fit assessment – manufacturing defects
• All microscopic techniques – reflectance and transmission modes (x700 for morphology)
• Microspectrophotometry – even more important when considering optically variable colours
• (ATR) Infrared spectroscopy – plastic chemistry
• Specific gravity – ensure colour fast first!
• Raman (micro) spectroscopy – polymer layers, can’t be used to detect aluminium
• SEM-EDX – microstructure detail and elemental composition of layers (aluminium)
• Physical characteristics are one of the most important parts.

Question 5

Analytical workflow for glitter

Additional information

Answer 5

• Physical fit doesn’t apply in the same way it does for paint
• Glitter particles are so small it’s highly unlikely it would break up and you’d be able to find a match
• Manufacturing defects can be almost as probative as a physical fit assessment.
• MSP is more important here than it is with any other form of trace evidence as the colours are optical variable.
• There is a huge amount of subjectivity when it comes to determining colour due to it looking different under different lights.
• Identify where it neither floats nor sinks between the two layers gives the gravity measurement but make sure you determine the colour first.

Question 6

Interpretation of glitter

Part one

Answer 6

• Number of particles and their physical dimensions
• Location of particles – context!
• Number, sequence, thickness and colour (beware subjectivity!) of layers
• Manufacturing defects, weathering, delamination, corrosion, damage.
• Location gives you crime reconstruction
• Manufacturing defects can be highly discriminatory and has high probative value.
• Potential to match the defects to an actual machine and therefore manufacturer.
• Oblique or alternate lighting as particles reflect differently
• Alternate between black, grey, and white backgrounds to facilitate colour determinations
• Q vs. K comparisons must be performed side-by-side using the same background colour
• ATR-FTIR for plastic chemistry – both sides!
• Currently, no forensic glitter database exists but would be much easier than for cosmetics
• Very limited research on background, transfer, persistence, activity level, etc.

Question 7

Intrepretation of glitter

Part two

Answer 7

• Glitter particle don’t necessarily have the same layer sandwiched on both sides
• Glitter takes years to degrade
• Substrate considerations (absence ≠ absence)
• Multiple associations mitigate coincidental transfer
• Nature of contact/forces involved
• Two-way transfer also applies but beware high retention → background levels.
• Glitter sticks really where but won’t stick well to shiny surface as well e.g satin or silk.
• Because it has such a high retention value background levels need to be considered when interpreting and determining context.
• Not quite as overlooked as cosmetic evidence – see case studies in the workshops…
• As with other types of trace → expensive, time-consuming, skilled analysis
• Small differences in peak intensities can be a discriminating factor
• Running a PCA could be helpful to pull the differences apart and give number stats.

Question 8

Why is glitter the ideal trace evidence?

Answer 8

• Highly individualistic, e.g. size, shape, thickness, specific gravity, morphology, number and thickness of layers, chemistry of layers, colour, special effects, manufacturer and/or geographical origin, cutting defects, vehicle, etc.
• Glitter is highly variable and they change a lot.
• SEM can detect difference in glitter cross sections
• Nearly invisible (until it catches the light!)
• High probability of transfer and retention
• Quickly collected, separated and concentrated
• Easily characterised (only a single particle required)
• Relatively persistent and resistant to degradation
• Unless its loose glitter it needs separating which is usually easy to do.
• Not effected by rain or UV radiation

Question 9

Drawbacks of glitter

Answer 9

Consumes a lot of microplastic

Question 10

Glitter alternatives

Answer 10

• Eucalyptus tree derived cellulose – Lyocell (rayon)
• Glass based glitter particles – The Unseen Spectra