trace evidence: paint criminalistics criminalistics

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  • Trace Evidence: Paint Criminalistics

  • Paint: binder, pigments and additives suspended in a solventBinderPigmentExtendersModifiersMajor Components

  • BinderPolymer (vehicle) that holds paint components together, forming a hard surface film as solvent evaporatesLacquer (evaporation of organic solvent)Enamel (chemical reaction of components)Latex (evaporation of water)Architectural

  • Pigment, Extenders, ModifiersPigmentColorOrganic: Blues & GreensInorganic: Whites, Yellows, RedsExtenders solid content, hiding ability/opacityTitanium dioxide acts as extender & pigmentModifiersGloss, hardness, flexibility, UV resistance, application, adhesion, drying

  • Automotive Paint LayersElectrocoat Primer on bare steel bodyCorrosion resistance, black, grayPrimer Surfacer smoothes imperfections Increases adhesion of basecoat to primerPigment added to minimize color contrast between primer and basecoatBasecoat /Color Coat Pigments, aluminum flakesClear CoatModifiers for durability, UV resistance

  • Paint as Physical EvidenceHit 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

  • Paint Chips from Scene

  • Paint AnalysisJigsaw MatchMicroscopic ExaminationChemical Analysis

  • QuestionedKnownJigsaw Match

  • Suspect vehiclePaint chips fm scene

  • Microscopic Examination of PaintStereomicroscope or Comparison MicroscopePhysical CharacteristicsColorSurface TextureNumber of layers Color sequence of layersThickness of layers

  • Electrocoat PrimerPrimer SurfacerBasecoat/ ColorcoatClearcoat

  • Chemical/Instrumental Analysis of PaintChemical AnalysisSolubility testsPyrolysis GC- decomposes paintIR MicrospectrophotometryIR absorption spectrum for each layerSEM-EDX or X-Ray Fluorescence (elemental composition)

  • Solubility Testing

  • Pyrolysis Gas Chromatography

  • Microspectrophotometer

  • IR Absorption Spectra of Paint

  • Investigative Information

    Upload IR spectra from Q sampleReceive:Make (Toyota, Ford, Chrysler, Chevy)GM- Chevy, Buick, Pontiac, CadillacModel (Corolla, Mustang, Sebring, Malibu)Corolla, Camry, SolaraYears of production

    Paint Data Query (PDQ)Database of Chemical & Color Information of Original Automotive Paints (>13,000 vehicles)

  • Paint Evidence CollectionCollect entire item, if possibleTools, clothing, bicycle, vehicleVehicle to vehicle transferAll layers of contactContainersPaper fold into envelopeVial (glass, plastic)Small cardboard box (larger paint chips)Keep paint chips intact Jigsaw match sometimes possible

  • Paint Evidence CollectionKnown/Reference SampleClean scalpel or knife bladeRemember possibility of Jigsaw MatchNear area of damage down to bare metalNear area of toolmark impression Package separately, note location

  • Collecting Known Sample

    ******** 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. ********************

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