trace evidence: paint criminalistics criminalistics

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