Paints: types and composition; Forensic examination of paint: microscopic and macroscopic examination, pigment distribution, micro-chemical analysis, physical matching and solubility test; Analytical tools used in paint comparison

1. PAINT EXAMINATION

2. Forensic Paint Analysis

3. PAINT AS EVIDENCE
*Double Transfer
*Locard’s Principle of Exchange

4. The Green River Killer - Worst American Serial Killer?
https://www.youtube.com/watch?v=IqqxHEtTvrA

7. Types of Paint
● architectural paint
● Product coatings
● special-purpose
coatings
● art paints

8. Paint composition
Sauzier, G., & Pitts, K. (2019).

9. Transfer and Persistence
properties of
the paint
(e.g.,
adherence
and quality),
the nature of
the
substrate
surface (e.g.,
rough and
smooth)
intensity of
the contact
(e.g., the
force or
pressure
involved).
Factors Affecting
transfer of paint
Factors Affecting Persistence
This Photo by Unknown Author is licensed under CC BY

10. General Packaging Considerations:
 Place samples into separate appropriately sized containers (e.g., do not
put very small items into very large envelopes) that help to prevent breakage
or loss
 Plastic should not be used for the packaging of small/loose trace evidence
due to static electricity.
 Do not pack with cotton or other protective material directly touching the
object.
 Do not package wet evidence. Clothing or objects containing paint
evidence should be air dried prior to packaging.
 paint chips can be collected using tape lifts with the least amount of
adhesive (e.g., magic tape) should be selected. Package tape lifts in clear
page protector sheets, plastic or Kapak bags.

11. PAINT AT
SCENE
All sample to be collected
PAINT ON
VEHICLE
Loose paint chips( glass vials or
cardboard pillboxes)
Transferred paint smears: Flake off
loose chips/cut around the around
using blade
Reference sample: Area from fresh
damage and adjacent to damage
PAINT ON
CLOTHING:
All clothing packed separately (paint
evidence packed in butter paper)

12. Aims of
Forensic
Paint
Analysis
Source: Muehlethaler et al. 2013

13. Paint Database
 European Collection of Automotive Paints (EUCAP)
https://www.nist.gov/oles/forensic-database-trace-
evidence-table
The French Police Lab
maintains the database; data
analysis is performed by the
Federal Criminal Police Force
of Germany (BKA).
paint samples removed from
primarily salvage vehicles by
law enforcement laboratory
participants throughout Europe.
The database can be accessed
via the internet via a secure ID
and password assigned by the
French Police Lab.

14. International Forensic Automotive Paint Data Query (PDQ)
Royal Canadian Mounted Police
(RCMP)-- Forensic Laboratory
Services
 a centralized, searchable
database of chemical and color
information of original
automotive paints.
 Search results provide
make/model/year information.
 PDQ contains foreign and
domestic automotive paint
samples from ~13,000 vehicles
and ~50,000 layers of paint.
 Most paint samples consist of
four layers typically used for an
automotive job.
 Contains majority of post-1973
vehicles marketed in the US.
 Law enforcement agencies
interested in PDQ who are not
already members can contact
PDQ directly by email.
 “Payment" for access to the
database is the submission of
60 samples to PDQ each year..

15. McCrone Microscopes &
Accessories
(commercial)
Paint Pigment Set - 50 Paint Pigment Set -
$325.00
McCrone Microscopes & Accessories - Slide Sets

16. National Automotive Paint File (NAPF)
Federal Bureau of
Investigations (FBI) -- FBI
Laboratory
 A physical collection of
automotive paint panels
acquired and maintained
by the FBI's Chemistry
Unit for use in
casework.
 NAPF is a physical
collection of paint color
standards and/or full
system paint panels (as
a vehicle would be
painted, not just the top
coats).
 It contains approximately
14,000 automotive paint
panels.
NAPF is used in an
investigation to make a
physical comparison of
evidentiary paint chips to
known paint colors to aid in
identifying possible vehicle
makes and models in hit-
and-run investigations.

17. Evidence Collection
Source: Muehlethaler et al. 2013
Record
collection
Control
sample
collection
Laboratory
collection

18. Source:Sauzier, G., & Pitts, K. (2019).

19. FORENSIC EXAMINATION OF PAINT SAMPLES

20. Visual examinations (A. Macroscopic examination/B. Microscopic examination or
Optical Examination )
Color, size, layers,
texture, and
general condition
Macroscopic
Examination
Number and
sequence of
layers
If not visible slice
the paint chip
embedded in resin
with razor blade or
scalpel blade)
Microscopic
examination
(stereomicroscope/
polarizing light
microscope,
Fluorescence
microscope etc)

21. Microscopic examination or Optical Examination )
Source: Muehlethaler et al. 2013
Source: Muehlethaler et al. 2013

22. Solubility and Microchemical Tests
*sample requirement: sufficient paint
material
*Solubility test chemicals: for paint
binders chemical reagents (e.g., chloroform,
acetone, or concentrated sulfuric acid).
*Microchemical tests: pigment and binder
color reactions.
*Disadvantages: destructive nature,
hazardous chemicals and larger sample
size requirements
Solvent test
(Chloroform
and
acetone)
How paint sample dissolving,
swelling, curling, softening or other
physical reactions
Chemical
reagents
diphenylamine (in concentrated
sulfuric acid and glacial acetic acid)
and Le Rosen (formaldehyde in
concentrated sulfuric acid) test.
dye solubility, pigment
effervescence, flocculation, and
color changes.

23. Physical match
The most definitive comparison that can be made between two otherwise
visually similar paint samples is the matching of reference and questioned
sample edges for a physical fit or matching the surface striae on the
underside of a paint fragment to those on a parent surface.
This assumes that the samples in question exhibit sufficient uniqueness for
comparison.
A. The edges (or striae) of the samples are visually examined macroscopically
and, if appropriate, microscopically for a physical fit.
B. Any physical fits should be documented by photography or video microscopy
or other appropriate means.

24. IR Spectroscopy
*sample preparation (KBr pellet
/squeezed in a microdiamond anvil cell)
*Component of paint identified
(organic and inorganic components of a paint
system, including mainly the binder, the extenders,
and some organic or inorganic pigments)
*FTIR Advantages
fast, repeatable, semi destructive
high discriminating power
commercial or forensic spectral databases exist
Source: Muehlethaler et al. 2013
Instrumental methods of analysis

25. Raman Spectroscopy
 Sample preparation (Paint traces can be analyzed in situ without any sample
preparation. Multilayered paint fragments are usually cut into thin cross-
sections and mounted on an aluminum foil so that each layer can be
analyzed independently)
 Component of paint identified (e organic and inorganic pigments and some
extenders)
 Advantages (absence of sample preparation and its very high spatial
resolution.)
 Disadvantages
 Its main disadvantage is the possible fluorescence of the sample, which will
totally or partially mask the Raman spectrum. One way of avoiding fluorescence
is to change the excitation wavelength (e.g., from the visible range to the
near-IR).

27. CASE STUDIES
Case 1 – vehicle
accident on the
motorway
During the night, two cars driving in
the same direction of the motorway
had a collision. In vehicle 1, a non-
metallic white-cream Toyota van, the
driver and two passengers were
present; the driver died in the accident
and the two passengers were gravely
injured. In vehicle 2, a blue metallic
Rover 200, only one person survived.
The survivors were asked about the
dynamics of the accident and each
one supplied a different version
Most traces were in form of
abrasive smears

28. Case 2 – burglary
case: paint traces on
a crowbar blade
A burglary was committed in a factory.
After breaking a window, the
perpetrator(s) entered the factory.
Once inside, a locked door separated
him (or them) from the safe. A tool was
used to force this door open. A
suspect car was stopped in the
surrounding area and from its boot a
red crowbar was seized.
Paint traces were observed on the
blade of the tool; the crowbar and
reference paints from the forced door
were sent to our laboratory.
Three groups of foreign paint traces
were observed on the blade of the red
crowbar: white, blue and pink. The
forced door was coated with a two-
layer paint system: blue and pink.

29. Case 3 – graffiti
on a vandalised
train
A Swiss regional train was tagged using different
colour spray paints: the colours were blue, white,
pink, black and green. The police asked our
laboratory to supply investigative information about
the brand and the sellers of such spray paints.
Raman and infrared spectroscopy were applied on
green spray paint traces

30. Case 4 – green paint
fragment on the
strap meshes of a
wristwatch
A person suspected of a crime was
temporarily detained in a provisory
detention cell. A writing of insults
was engraved on the green coated
wall of the cell. The police officer
suspected that the golden
wristwatch of the suspect was
used to engrave the writings.
Foreign paint traces were
searched on the watch: only one
small fragment was observed in
the internal side of the strap
meshes of the gold-coated watch

31. Case 5 – the
surprise eggs
case
One morning, Mr X noticed
a big red stain on the
outside wall of his house
and some broken eggshells
with red material on the
ground. Someone had filled
empty eggs with red paint
and thrown them on the
wall. The broken eggshells
were collected by the
police. His neighbour was
suspected, but no red paint
was found in his house.
However, a pair of shoes
was seized on which some
small red paint droplets
were observed

32. Pyrolysis–Gas Chromatography–Mass Spectrometry
 Sample reqirement (A minimum of 10 mg is necessary for the analysis.
Each layer of a paint flake must be isolated prior to analysis)
 Component of paint identified (paint binders will decompose into smaller
volatile fragments./might detect additives or pigments if reference
pyrograms and/or MS spectra are available.)
 Advantages (its high discriminating power and its ability to detect and
compare minor constituents.)
 Disadvantages
destructive nature and time-consuming analysis

33. Elemental Analysis (Scanning Electron Microscopy/Energy Dispersive x-Ray Analysis,
Micro x-Ray Fluorescence)
Source: Muehlethaler et al. 2013
*sample preparation (Multilayer samples have to be prepared (by embedding, polishing, or sectioning).)
*Component of paint identified (This technique will mostly characterize the extenders and inorganic pigments as well as
some organic pigments.)
*Advantages The analyses are rapid and rather sensitive (0.1 wt%) and provide complementary information as against
FTIR, Raman, and Py–GC/MS, which mostly characterize the organic components of a paint

34. Microspectrophotometry
Source: Muehlethaler et al. 2013
*sample preparation (. It requires some sample preparation and quartz
microscope slides.)
*Component of paint identified ()
*Advantages/Disadvantages (MSP can provide an objective measure of the
color and might be able to differentiate between optically identical samples
(metamers). However, this method is more problematic for effect coatings and
measurements must be carried out on clean and undamaged sample areas of
similar size and morphology.
Source: Muehlethaler et al. 2013
Source: Muehlethaler et al. 2013

35. Determination of the
Significance of an
Association
Levels of
Association
Level 1:
Identification
Level 2: High
degree of
association in
which the
evidence
contains
unusual
characteristics
Level 3:
Conventional
association
Level 4:
Limited
association
Level 5:
Inconclusive
Level 6:
Elimination/ex
clusion

36. References
● Muehlethaler, C., Gueissaz, L., & Massonnet, G. (2013). Forensic paint analysis.
● Bender, L. (2013). Interpretation of Paint Evidence. in-Chief: Jay, JS Pekka (Eds.) Encyclopedia of Forensic
Sciences, Academic Press, Waltham, 273-278.
● Sauzier, G., & Pitts, K. (2019). Forensic Sciences| Paints, Varnishes, and Lacquers.
● https://www.youtube.com/watch?v=KRoWMB3AR3s (FTIR spectroscopy)
● https://www.youtube.com/watch?v=SsIYDEma_cU&ab_channel=PracticalNinjas (Raman Spectroscopy)
● https://www.youtube.com/watch?v=J8eYFLhQMeo&ab_channel=YoungInChromassGlobal (py GC-MS)
● https://www.youtube.com/watch?v=GY9lfO-tVfE&ab_channel=MaterialsScience2000 (Scanning electron microscope)