1. Trace Evidence: Paint
Criminalistics

2. Paint: binder, pigments and additives suspended in a solvent
Major Components
Binder
Pigment
Extenders
Modifiers

3. Binder
Polymer (vehicle) that holds paint components together, forming a hard surface film as solvent evaporates
Lacquer (evaporation of organic solvent)
Enamel (chemical reaction of components)
Latex (evaporation of water)
Architectural

4. Pigment, Extenders, Modifiers
Color
Organic: Blues & Greens
Inorganic: Whites, Yellows, Reds
Extenders
↑ solid content, hiding ability/opacity
Titanium dioxide acts as extender & pigment
Modifiers
Gloss, hardness, flexibility, UV resistance, application, adhesion, drying

5. Automotive Paint Layers
Electrocoat Primer on bare steel body
Corrosion resistance, black, gray
Primer Surfacer smoothes imperfections
Increases adhesion of basecoat to primer
Pigment added to minimize color contrast between primer and basecoat
Basecoat /Color Coat
Pigments, aluminum flakes
Clear Coat
Modifiers for durability, UV resistance

6. Paint as Physical Evidence
Hit and Run/MVAs- Paint fragments or smears transferred to clothing (pedestrian) or another vehicle (vehicle to vehicle)
Burglaries- Paint smears transferred onto a tool or point of entry (tool mark)

8. Scrape down clothing for Trace Evidence
An efficient and effective method of recovering very small paint and glass particles from the clothing of Hit and Run victims, is the “Shake and Scrape” Method. A garment is shaken and scraped with a large spatula over a large sheet of paper to collect any loosely adhering trace particles, especially paint particles from vehicles involved in Hit and Runs.

11. Paint Chips from Scene

12. Paint Analysis
Jigsaw Match
Microscopic Examination
Chemical Analysis

13. Jigsaw Match
Known
Questioned

14. Suspect vehicle
Paint chips fm scene

15. Microscopic Examination of Paint
Stereomicroscope or Comparison Microscope
Physical Characteristics
Color
Surface Texture
Number of layers
Color sequence of layers
Thickness of layers

16. Clearcoat
Basecoat/ Colorcoat
Primer Surfacer
Electrocoat Primer

17. Chemical/Instrumental Analysis of Paint
Chemical Analysis
Solubility tests
Pyrolysis GC- decomposes paint
IR Microspectrophotometry
IR absorption spectrum for each layer
SEM-EDX or X-Ray Fluorescence (elemental composition)

18. Solubility Testing

20. Pyrolysis Gas Chromatography

21. Microspectrophotometer

22. IR Absorption Spectra of Paint

23. Investigative Information
Paint Data Query (PDQ)
Database of Chemical & Color Information of Original Automotive Paints (>13,000 vehicles)
Upload IR spectra from Q sample
Receive:
Make (Toyota, Ford, Chrysler, Chevy)
GM- Chevy, Buick, Pontiac, Cadillac
Model (Corolla, Mustang, Sebring, Malibu)
Corolla, Camry, Solara
Years of production

26. Paint Evidence Collection
Collect entire item, if possible
Tools, clothing, bicycle, vehicle
Vehicle to vehicle transfer
All layers of contact
Containers
Paper fold into envelope
Vial (glass, plastic)
Small cardboard box (larger paint chips)
Keep paint chips intact
Jigsaw match sometimes possible

27. Paint Evidence Collection
Known/Reference Sample
Clean scalpel or knife blade
Remember possibility of Jigsaw Match
Near area of damage down to bare metal
Near area of toolmark impression
Package separately, note location

28. Collecting Known Sample