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Trace Evidence: Paint Criminalistics Criminalistics.

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

1 Trace Evidence: Paint Criminalistics Criminalistics

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

3 Binder Polymer (vehicle) that holds paint components together, forming a hard surface film as solvent evaporates 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 Pigment –Color »Organic: Blues & Greens »Inorganic: Whites, Yellows, Reds Extenders Extenders –↑ solid content, hiding ability/opacity –Titanium dioxide acts as extender & pigment Modifiers Modifiers –Gloss, hardness, flexibility, UV resistance, application, adhesion, drying

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

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8 Scrape down clothing for Trace Evidence

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11 Paint Chips from Scene

12 Paint Analysis Jigsaw Match Jigsaw Match Microscopic Examination Microscopic Examination Chemical Analysis Chemical Analysis

13 Questioned Known Jigsaw Match

14 Suspect vehicle Paint chips fm scene

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

16 Electrocoat Primer Primer Surfacer Basecoat/ Colorcoat Clearcoat

17 Chemical/Instrumental Analysis of Paint Chemical Analysis 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

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20 Pyrolysis Gas Chromatography

21 Microspectrophotometer

22 IR Absorption Spectra of Paint

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

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

27 Paint Evidence Collection Known/Reference Sample 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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