Trace Evidence: PaintTrace Evidence: Paint
CriminalisticsCriminalistics
Paint: binder, pigments and Paint: binder, pigments and additives suspended in a solventadditives suspended in a solvent
BinderBinder PigmentPigment ExtendersExtenders ModifiersModifiers
Major Components
BinderBinder
Polymer (vehicle) that holds paint components Polymer (vehicle) that holds paint components together, forming a hard surface together, forming a hard surface film film as as solvent evaporatessolvent evaporates
– Lacquer (evaporation of organic solvent)Lacquer (evaporation of organic solvent)
– Enamel (chemical reaction of components)Enamel (chemical reaction of components)
– Latex (evaporation of water)Latex (evaporation of water)» ArchitecturalArchitectural
Pigment, Extenders, ModifiersPigment, Extenders, Modifiers PigmentPigment
– ColorColor» Organic: Blues & GreensOrganic: Blues & Greens
» Inorganic: Whites, Yellows, RedsInorganic: Whites, Yellows, Reds
ExtendersExtenders– ↑↑ solid content, hiding ability/opacitysolid content, hiding ability/opacity– Titanium dioxide acts as extender & pigmentTitanium dioxide acts as extender & pigment
ModifiersModifiers– Gloss, hardness, flexibility, UV resistance, Gloss, hardness, flexibility, UV resistance,
application, adhesion, dryingapplication, adhesion, drying
Automotive Paint LayersAutomotive Paint Layers
Electrocoat PrimerElectrocoat Primer on bare steel body on bare steel body Corrosion resistance, black, grayCorrosion resistance, black, gray
Primer SurfacerPrimer Surfacer smoothes imperfections smoothes imperfections Increases adhesion of basecoat to primerIncreases adhesion of basecoat to primer Pigment added to minimize color contrast between Pigment added to minimize color contrast between
primer and basecoatprimer and basecoat BasecoatBasecoat / /Color CoatColor Coat
– Pigments, aluminum flakesPigments, aluminum flakes Clear CoatClear Coat
– Modifiers for durability, UV resistanceModifiers for durability, UV resistance
Paint as Physical EvidencePaint as Physical Evidence
Hit and Run/MVAsHit and Run/MVAs- Paint fragments or - Paint fragments or smears transferred to smears transferred to clothingclothing (pedestrian) (pedestrian) oror another another vehicle vehicle ((vehicle to vehiclevehicle to vehicle))
Burglaries-Burglaries- Paint smears transferred onto a Paint smears transferred onto a tool tool oror point of entry point of entry (tool mark)(tool mark)
Scrape down Scrape down clothing for clothing for
Trace EvidenceTrace Evidence
Paint Chips from Scene
Paint AnalysisPaint Analysis
Jigsaw MatchJigsaw Match
Microscopic ExaminationMicroscopic Examination
Chemical AnalysisChemical Analysis
Questioned
Known
Jigsaw Match
Suspect vehicle
Paint chips fm scene
Microscopic Examination of PaintMicroscopic Examination of Paint
Stereomicroscope or Comparison Stereomicroscope or Comparison MicroscopeMicroscope
Physical CharacteristicsPhysical Characteristics– Color– Surface Texture– Number of layers – Color sequence of layers– Thickness of layers
Electrocoat Primer
Primer Surfacer
Basecoat/ Colorcoat
Clearcoat
Chemical/Instrumental Analysis of PaintChemical/Instrumental Analysis of Paint
Chemical AnalysisChemical 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 InformationInvestigative Information
Upload IR spectra from Upload IR spectra from QQ sample sample Receive:Receive:
– MakeMake (Toyota, Ford, Chrysler, Chevy) (Toyota, Ford, Chrysler, Chevy)» GM- Chevy, Buick, Pontiac, CadillacGM- Chevy, Buick, Pontiac, Cadillac
– ModelModel (Corolla, Mustang, Sebring, Malibu) (Corolla, Mustang, Sebring, Malibu)» Corolla, Camry, SolaraCorolla, Camry, Solara
– YearsYears of production of production
Paint Data Query (PDQ)
Database of Chemical & Color Information of Original Automotive Paints (>13,000 vehicles)
Paint Evidence CollectionPaint Evidence Collection Collect entire item, if possibleCollect entire item, if possible
Tools, clothing, bicycle, vehicleTools, clothing, bicycle, vehicle Vehicle to vehicle transferVehicle to vehicle transfer
All layers of contactAll layers of contact ContainersContainers
Paper fold into envelopePaper fold into envelope Vial (glass, plastic)Vial (glass, plastic) Small cardboard box (larger paint chips)Small cardboard box (larger paint chips)
Keep paint chips intact Keep paint chips intact Jigsaw match sometimes possibleJigsaw match sometimes possible
Paint Evidence CollectionPaint Evidence Collection
Known/Reference SampleKnown/Reference Sample Clean scalpel or knife bladeClean scalpel or knife blade Remember possibility of Jigsaw MatchRemember possibility of Jigsaw Match NearNear area of damage down to bare metal area of damage down to bare metal NearNear area of toolmark impression area of toolmark impression Package separately, note locationPackage separately, note location
Collecting Known Sample