Lecture 14 - Makeup Part 2 Flashcards
1
Q
What are interference pigments also known as?
A
- Shimmer
- Made from metal oxide layers (TiO2, Fe2O3, Fe3O4, BiOCl, SnO2, carmine, ferric ferrocyanide, chromium oxide) on a mica substrate around ~500nm thick.
- Shimmer and glitter are not interchangable
- Mica is a naturally occuring silicate material which comes in various forms.
2
Q
Mica
A
- Mica is a naturally occurring silicate material which comes in various forms
- Mineral itself is a flaky rock
- They coat the mica substrate of different layers of metal oxides which give different interference effects
- When layered on mica is interference but on its own its pearlescent
- Various mica based interference pigments
- As the thickness of oxide increases it changes the colour we see.
- Mica has a lower RI but TIO2 has a high RI this difference in RI gives the interference effect as it effects the way light transmits through and reflects off.
3
Q
What dictates the colour of interference pigments
A
- Thickness of metal oxide layers (and type thereof) dictate colours reflected and transmitted.
- Thickness, type, number and sequence of metal oxide layers will determine the colour reflected and transmitted.
4
Q
Alternative substrates to mica
A
- Borosilicate glass, silica and alumina
- These are thinner and more uniform than natural mica so we can control the sruface to make them flatter and smoother
- They are colourless whereas mica is slightly yellow
- Low RI than mica which increases the interference.
- Mica is a naturally occuring matieral and is a finite resource.
5
Q
SEM imaging for interference pigments
A
- Secondary electron mode is better at looking at surfaces, topology, texture.
- Backscatter is better at looking at difference in density or chemical composition based on weight of atoms involved.
6
Q
Size of pigment particle
A
- Size of pigment particle will dictate how intese the effct is.
- Larger particle size = larger flajes = more brighter finish
7
Q
Recovery considerations of makeup
A
- Air dry wet garments in controlled environment
- Store in paper bags to prevent mould growth
- Never package along with debris from the scene.
- Cosmetic traces likely to adhere better to garments/bedding/upholstery/carpets.
- Makeup is not a solid material so once applied to face it mixes with body materials and sweat so it becomes a liquid and adheres better.
- Whole item recovered is preferable.
- If the substrate is large/immovable, samples to be collected to encompass both transfer and substrate – use scalpel blade
- Refrigeration dependant upon presence of DNA traces → preferable to keep evidence at room temperature.
- Protect area where the stain is to stop it transferring to other areas of trh substrate as location is important
8
Q
Makeup analytical workflow
A
- Gross examination, recovery and collection
- Preliminary evaluation of physical characteristics
- (Physical fit assessment – most probative value)
- Physical fit isn’t applicable when dealing with liquid transfer
- All microscopic techniques (fluorescence)
- Experts recommend fluorescence is useful for makeup
- Microspectrophotometry – colour determination
- Infrared spectroscopy – organic content/silicones
- Raman spectroscopy – inorganic pigments
- SEM-EDX – SE mode for surface topology & BSE mode for homogeneity
- XRF – elemental composition
- XRD – crystal structure, polymorphs
- (Pyrolysis-GC/MS)
- (Microchemical tests)
9
Q
Makeup analysis
A
- Observations to record include general item type, dimensions, manufacturer’s labels (if a garment), markings, colour, logos/insignias, condition/damage
- Document colour and location of suspected cosmetic transfers
- Once visual analysis is completed go straight to stereomicroscope for further inspection
- Consider oblique or alternate lighting – particles reflect differently, e.g. interference pigments
- 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
- Transmitted light for observing pigment distribution; reflected light for layers or textures – use both!
- Interference pigments are shown as different colours depending on the angle of incident light and the angle you observe them
- Backgrounds will affect what we sill, particularly if the pigments are translucent
- Different lights pick up different aspects of the pigment you’re looking at.
10
Q
Colour analysis
A
- ## Colour analysis to include hue, value (brightness) and chroma (saturation) provides the basis for HVC classification.
11
Q
Munsell’s Colour Theory → 3D model
A
- Hues → five main plus five combinations
- Values (how light or dark a sample is)→ 0 = black, 10 = white
- Chroma → 0 = neutral, arbitrary end ~15-20 (~30)
- 5 main colours: red, purple, blue, green, yellow.
- Model has no end.
- Fluorescent pigments are bright so it would have values around 30.
12
Q
Chroma
A
Chroma is the intensity and pureness of colour, it goes from center to outwards on the model.
13
Q
Microscopic analysis
Observable differences
A
- Colour matrix/particles
- Distribution of pigments
- Particle morphology
- Surface topology
- Mica vs. synthetic (also SEM-EDX!)
- Borosilicate glass
- PMMA/silica spheres (also RI measurement)
- Component encapsulation
- Different number and sizes of pigments
- Differences in mica plates
14
Q
Mica differences
A
- Mica can be created synthetically but is also naturally occurring
- Synthetic version contains fluorine so we can discriminate using SEM-EDX
- Fluorine indicates synthetic mica
- Distinction between borosilicate glass and natural mica substrates in interference pigments
- Borosilicat is slightly more translucent and has sharper edges due to it being glass
- Mica has a more natural look, it has rounded edges, difference in thickness and less uniform.
15
Q
Cosmetic interpretation
A
- Class characteristics (producvt type)
- Indivudal characteristics (mixtures)
- Chemical differences (pigments)
- Rarity of makeup increases probative value
- Raman spec allows us to get further down on the wavelength scale.
- Because people use lots of different products in different ways with different application methods with different skin we get high discrimination.
- Cosmetic formulations not shared which can make analysis difficult.
- No forensic cosmetic database.
- Very limited research on background, transfer, persistence, contamination and activity level
- Number and location of transfers found
- Substrate considerations (absence ≠ absence)
- Multiple associations mitigate coincidental transfer
- Nature of contact/forces involved
- Two-way transfer also applies!
