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Trace Evidence: Paint Criminalistics.

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Presentation on theme: "Trace Evidence: Paint Criminalistics."— Presentation transcript:

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

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