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Trace Evidence: Paint

Trace Evidence: Paint. Criminalistics. Paint: binder, pigments and additives suspended in a solvent. Binder Pigment Extenders Modifiers. Major Components. Binder. Polymer (vehicle) that holds paint components together, forming a hard surface film as solvent evaporates

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Trace Evidence: Paint

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  1. Trace Evidence: Paint Criminalistics

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

  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 • Pigment • 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)

  7. Scrape down clothing for Trace Evidence

  8. Paint Chips from Scene

  9. Paint Analysis • Jigsaw Match • Microscopic Examination • Chemical Analysis

  10. Jigsaw Match Known Questioned

  11. Suspect vehicle Paint chips fm scene

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

  13. Clearcoat Basecoat/ Colorcoat Primer Surfacer Electrocoat Primer

  14. 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)

  15. Solubility Testing

  16. Pyrolysis Gas Chromatography

  17. Microspectrophotometer

  18. IR Absorption Spectra of Paint

  19. 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

  20. 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

  21. 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

  22. Collecting Known Sample

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