Trace Evidence: Paint Criminalistics.

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Presentation transcript:

Trace Evidence: Paint Criminalistics

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

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

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

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

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)

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.

Paint Chips from Scene

Paint Analysis Jigsaw Match Microscopic Examination Chemical Analysis

Jigsaw Match Known Questioned

Suspect vehicle Paint chips fm scene

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

Clearcoat Basecoat/ Colorcoat Primer Surfacer Electrocoat Primer

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)

Solubility Testing

Pyrolysis Gas Chromatography

Microspectrophotometer

IR Absorption Spectra of Paint

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

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

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

Collecting Known Sample