Trace Evidence Final

white pigments

-inorganic pigment with a low RI & low cost found in most paints due to hiding capabilities -titanium dioxide, antimony trioxide, zinc pigments, lead

refinishes

-inside the manufacturing plant (usually same paint chemistry as the original paint, may be different color) -outside manufacturing plant (alkyd enamels, acrylic alkyd enamels, acrylic modified nitrocellulose lacquers, acrylic urethane enamels & acrylic lacquers)

determining if refinish is inside or outside manufacturer

-inside: layer 3=5 (basecoats) & layer 4=6 (clearcoats) -outside: layer 5 & 6 would most likely not be similar chemistries as layers 3 & 4

pepper spray

-is a lachrymator: an inflammatory agent that irritates the eyes, causing tears, pain & eventually temporary blindness -causes immediate closing of eyes, difficulty breathing, runny nose, coughing -active ingredient is capsaicin derived from peppers, soluble in fats/oils but not water -analyzed with GC/MS

automotive paint trends

-2/3 pounds of solvent used instead of 7 -UV cure clear coat: heat source near scratch in clear coat will repair it -3 WET integrated system: top 3 coats applied then baked -magnetic imager effect: magnets align the pigments, used for logos/designs

epoxy resins

-hard, durable, chemically strong, & resistant to attack resins -used on manufactured products -bisphenol A (BPA): chemical/corrosion resistant, used for interior beverage/food containers

positive pGSR conclusion

-3 or more characteristic pGSR particles observed -particles containing lead, barium, & antimony were detected on the item, consistent with pGSR. The presence of pGSR may occur because the subject may have discharged a firearm or been in the vicinity of a firearm when it was discharged, or handled an item with pGSR on it

architectural paint

-Coatings encountered in households or places of business -Typically oil-based alkyds and water-based emulsions

extenders

-Modify gloss, viscosity, flow, smoothness of film, & texture -usually found in non-gloss or flat architectural paint -barium sulfate, calcium sulfate, calcium carbonate, silicate pigments

pGSR analysis

-SEM/EDS: non destructive, automated analysis -minimal sample prep: carbon coating for better conductivity -automated searches are configured to see bright particles due to grey levels set by operator -operator confirms morphology & elemental composition of particles

mace

-a tear gas aerosol spray -1% CN tear gas in a solvent -causes burning sensation, automatic closing of eyes, difficulty breathing -analyzed with GC/MS

driers

-added to promote faster drying time of oils -typically metallic soaps (salt of monocarboxylic acid & a metal) of lead, zirconium & calcium, zinc, aluminum, barium, cobalt & manganese

leafing flakes

-aluminum flakes compounded with stearic acid, which allows the flakes to float to the surface -uniform silver colored surface -can't be tinted with other pigments/dyes

non-leafing flakes

-aluminum flakes that orient randomly & can be tinted with color

miscellaneous paint additives

-anti foam, anti mildew, anti skinning, freeze thaw stabilizers, anti sag, coalescing & thickening agents -typically in small concentrations, unable to detect in small amount of dried paint

Anti-chip coating

-applied between the e-coat primer & the primer surfacer on the undercarriage & lower body panels of the auto vehicle -urethane cross linking resin

primer surfacer

-applied over the e-coat as a powder -fills surface imperfections & creates adhesion of the color coat to the automobile -epoxy modified polyesters & acrylic powders -highly pigmented to minimize the color contrast b/w the primer & basecoat (light grey under pastels, red oxide under dark colors)

topcoat application

-basecoat applied & flashed -clearcoat applied & flashed -both coats baked to promote cross linking -typically thickest layer on car

plastic substrates

-bumpers, door panels, rear decks, front grills -basecoat applied directly to it, no primers or electrodeposition -cured by UV, IR curing would melt it

inorganic colored pigments

-can be synthetic or natural pigments -natural: usually used for artist's oil paint -ROYGBIV & brown

MSP analysis (paint)

-can discern differences in the absorption of light in similar appearing color samples -organic dyes create pronounced inflections in the spectra (great discriminating power) -disadvantages: inorganic pigments create broad absorption bands that are featureless, irregular surface of the paint can cause light scattering, lack of reproducibility in the same sample

lacquer

-clear or pigmented fast drying coating -dries by evaporation, rather than polymerization or oxidation

PLM analysis (paint)

-comparison & identification of particles in the paint (pigments, extenders, additives, contaminants) -examine thin peels, cross sections, dispersed particles in mounting media -reflected & transmitted light

Amino Resins

-condensation product of formaldehyde with urea or melamine -acts as cross linking agent for thermosetting alkyds, acrylics, & epoxies -melamine: better cross linker & more weather resistant -benzoguanamine: more flexible, better bond strength -brittle, requires plasticizing action of another resin

bank dye packs

-contains 1-Methylaminoanthraquinone (1-MAAQ) -red dye that stains money, the suspect, clothing, & getaway vehicle -designed to draw attention & explosion can injure suspect -may also contain tear gas: causes abandonment of source (money) and or getaway vehicle, leaves odor that can draw attention & help identify suspect

metal pretreatment

-corrosion protection for auto vehicles -metals & plastics are cleaned/scrubbed -electrogalvanized conversion coating layer: plate like crystals of zinc phosphate are electrolytically grown on the surface of metals

RCMP/FBI paint data query (PDQ)

-database with info on layer structure, primer colors, primer binders, pigment & topcoat binder chemistry -FTIR spectra for layer sequences can be compared to case FTIR spectra -provides make/model/year info of vehicles used today

PY-GC/MS analysis (paint)

-discriminates b/w similar paint binders from different manufacturers -discriminates b/w alkyd drying oils -effective w non gloss highly pigmented architectural paints -disadvantages: destructive, 5-10x amount of sample needed compared to FTIR, substrate contamination & carryover is common

where pGSR is expelled from

-ejection port of the hand gun -cylinder of the revolver -not expelled at all

automotive 4 layer system

-electrocoat primer -primer surfacer -topcoats: basecoat/color coat & clear coat

electrodeposition (e-coat) primer

-electrodeposited on steel body then baked -provides corrosion resistance -epoxy resins cross linked with isocyanates, some use of acrylics -titanium dioxide, talc added for film reinforcement -carbon black added as corrosion inhibitive pigment -color: black to grey

plastic bags

-flexible packaging made of thin, flexible, plastic film -polyethylene most common -polypropylene, PVC, tyvek, cellophane -individuality: contamination of vat of material, extrusion marks from manufacturing process, physical match with perforations -analysis: color, thickness, length/width, physical characteristics, FTIR

Urethane Resins

-isocyanates with hydroxyl containing materials (polyesters & alcohol based drying oils) -1 component system: similar to alkyd resins with an oil introduced -2 component system: resin + hardener/catalyst, highly durable film, quick application but difficult to apply, used in high volume manufacturing, used for plastic substrates (not tolerant to high temp cures)

elemental composition of pGSR particles

-lead, barium, & antimony -low levels or absent iron -absent magnesium -trace levels of other elements

alkyd resins

-linear & cross linked polymers of alcohols & acids -modified with oils, fatty acids, & other resins to make more soluble, less brittle resins -used in oil based paints for household use

resin vehicles/binders

-material able to change from a solution into a self sustaining film, always polymers -ex: alkyd, polyester, acrylic, vinyl, urethane, epoxy, silicone, amino

latex gloves

-may find box in suspect's home or car -link crimes of similar type -powder & powder free varieties -analysis: color, thickness, length/width, physical characteristics, FTIR analysis

automotive paint process

-metal pretreatment -electrodeposition (e-coat) primer electrodeposited on metal parts -anti chip coating may be applied to the lower body panels -primer surfacer applied -finish/top coats applied: basecoat & clear coat

morphology of pGSR particles

-molten like, often spherical -rapid cooling of the discharged gases & solid matter -condenses into spheres -interact with solid residue to form complex mixtures & aggregate forms -evidence of exposure to or formation at extremely high temperature & pressure

sinoxid

-most common primer in US -composed of lead styphnate, barium nitrate, & antimony sulfide

oils

-naturally occurring triglycerides which form a film by oxidation, dries to a soft/flexible coating -vegetable & fish origin -found in household paints, raw material for varnishes, & feedstock for alkyds, epoxy-ester resins, oil modified urethane resins & plasticizers -can be drying, semi drying, or non drying -drying property based on extent of unsaturation of the fatty acids (more double bonds = faster dry)

negative (no particles) conclusion

-no pGSR detected on item -this absence may occur because the subject may not have discharged a firearm, may have discharged a firearm but no pGSR particles were deposited on the sampled area, or may have discharged a firearm but the pGSR particles were removed by washing, wiping, etc

FTIR w microscope attachment (paint)

-obtain chemical info about the binders, pigments, & additives -most discriminating technique for paint -extensive libraries for comparison -small samples analyzed w diamond compression cell -disadvantages: not reliable for minor components, acrylic lacquer & alkyd enamels not easily discriminated -far IR region: can identify inorganic topcoat pigments

Airless Spray Technology

-paint application technique that atomizes the paint into tiny droplets at high velocities -electrostatic charge given to droplets so they are attracted to the vehicle

Powder Technology

-paint application technique where negatively charged particle powders are attracted to the electrically grounded car parts -cured to film by heat, UV radiation or electron beam -primer surfacers applied with this process -most expensive process for manufacturer

metallic pigments

-pigment in flake or powder form for aesthetic purposes -automotive finishes: glittering effect -aluminum flakes most common

black pigments

-pigments that include black iron oxide, coal, & bone black, & carbon black manufactured from combustion of oil & gas -most common is carbon black

Pearlescent Pigments

-pigments that mimic luster of natural pearls for aesthetic purposes -high RI on thin transparent flakes -color produced by interference effects -titanium dioxide or ferric oxide are coated on mica or bismuth oxychloride flakes, thickness determines tint & hue

organic colored pigments

-pigments with a huge variety in hue & performance based on chemical composition & modifying groups -ROYGBIV

vinyl resins

-polymerization of vinyl chloride, vinyl acetate and respective copolymers -used to modify other resins -increases polarity to produce water based latex systems -PVC powder coatings can be used as bake coatings on metal furniture, pipes, or fencing

antimony free & environmentally safe primers

-primers that are more common outside the US -uses lead styphnate, barium sulfate, & calcium silicide -tin foil in the primer cup

binder

-provide the support medium & even coating of the pigments & additives in paint -binds pigments to the substrate & to another layer of paint (synonymous with vehicle)

acrylic resins

-resins made from acrylate & methacrylate monomers -modified with polyesters, amines, urethanes, styrene, & epoxies -available as water based latex coatings, lacquers, & thermosetting resins -used to modify other urethane & alkyd resins -thermoplastic: household use -thermosetting: appliances & previously used on cars, replaced by urethanes

condom lubricants

-silicone based: low molecular weight silicone oil, polydimethylsiloxane (PDMS), easier to detect -water soluble: polyethylene glycol (PEG), harder to detect -spermicide: nonoxynol-9, in very small amounts -starch, flavors, coloring, fragrance, etc -factors affecting detection: washing, menstruation, systematic absorption -analysis: look for starch granules under crossed poles with PLM, FTIR (can't discriminate b/w PDMS based lubricants, PEG unlikely to be found), GC/MS

silicone resins

-siloxane bond based, modified by other copolymers -curing requires 1 hour at temps > 200C -used in industrial settings (undercarriages of vehicles) -modifier of other resins

polyester resins

-similar to alkyds but they do not incorporate drying oils -require cross linkers or resins to cure (heat)

stain

-solution or dye or pigment used to color wood -no binder added, used only to color not coat

negative (less than 3) conclusion

-state number of particles containing lead, barium, & antimony on item -the subject may have discharged a firearm but no pGSR particles were deposited on the sampled area, or may have discharged a firearm, however the pGSR particles were removed by washing, wiping, or other activity before the samples were collected

size of pGSR particles

-sub micrometer to several hundred micrometers -often around 1-5 um

cosmetics

-substances used to enhance or protect appearance or odor of the human body -strong red color uses dye carmine extracted from crushed bodies of insects -pearlescence: shine or gloss effects, mica with a thin layer of titanium dioxide most common, suspension of tiny flakes in wax or glycerol distearate found in fish scales (used in nail polish) -analysis: PLM (crystals, mica flakes, pigments, size of particles, birefringence, extinction, RI) -SEM/EDS: synthetic pearl pigments, barium & calcium colors, natural pigments, fillers -FTIR: organic components, fillers -GC/MS: castor oils, fatty materials, waxes

paint

-suspension of a pigment (color) in a vehicle (binder) -any surface coating designed for protection of a surface or for decoration purposes

bank dye evidence analysis

-take cutting or swab with solvent (methanol or acetone) on money, clothing, or containers as well as control -GC/MS electron impact most used for analysis -solubility test in methanol & FTIR also used

basecoat

-top coat that provides color & aesthetics (must be weather resistant: acid rain & UV radiation) -pearlescent look: pearl luster/mica pigments -metallic look: aluminum flakes -acrylic/polyester melamine polymers

monocoat

-topcoat with no clear coat layer -acrylic, urethane, & alkyd cross linked with melamine or isocyanate resin

how pGSR is created

-trigger is pulled -firing pin hits the primer cap -primer compounds ignite, make a flame -flame ignites the gunpowder, which then explodes -gunpowder burns, creating gas -gas pushes the projectile/bullet down the barrel of the gun

clear coat

-unpigmented topcoat that contains UV absorbers & hindered amine light stabilizers (improves gloss, durability, & appearance, provides etch resistance, prevents yellowing) -acrylic based or 2 component polyurethane resins

pGSR collection

-use SEM stub on suspect shooter's hands, clothing, or other objects -4 hour window for hands -"uncontaminated collectors"- non police officers

shellac

-used as a sealant, adhesive or insulating varnish -made from excretions of certain insects

solvents

-used to dissolve the binder & create consistency -dissolves film formers, creates uniform distribution of film formers & pigments -evaporates as the paint dries, typically before forensic analysis -Ex: terpenes, naphtha, alcohols, ketones, esters, etc

plasticizers

-used to increase flexibility & workability of the paint -create superior weathering properties & impact resistance -most common: di-2-ethylhexyl phthalate (DOP)

color analysis (paint)

-view edge of paint chip with a contrasting background under stereomicroscope -count number, sequence, & relative thickness of layers -cross section: embed the chip to be sectioned by microtome or do by hand

physical match (paint)

-when known & unknown samples can be placed back together in unique manner -examine for irregular contours, surface scratches, surface markings, & check underside -if made, no further examination required

varnish

clear homogeneous solution of drying oils & resins in organic solvents

antimony sulfide

component of sinoxid primer that is the fuel & burns at a higher rate & ignites the gunpowder in the cartridge case

Lead Styphnate

component of sinoxid primer that is the initiator, is shock sensitive, & ignites when the primer cap is struck by the firing pin

barium nitrate

component of sinoxid primer that is the oxidizer & gives up oxygen to maintain combustion

fluorescence microscope (paint)

excitation wavelength of 365 nm may show differences in organic pigments, additives, & film forming components

pigment

finely powdered solid dispersed & insoluble in a coating vehicle

Types of Tear Gas

CS or CN

monomer

one unit

enamel

pigmented coating that dries to a hard gloss

interference pigments

pigments with excellent hiding power & chromatic shifts based on viewing angle & have a wide variety of available colors

cross linking polymers

backbones joined in a 3D array

Thermosetting polymer

resin cross-links when baked (requires heat)

thermoplastic polymer

resin polymerizes without heat

coating

surface covering applied to provide color, protection, corrosion resistance, etc (synonymous with paint)

latex

suspension of pigments in a water- based emulsion of any resins

crime scene collection of paint samples

use razor blade to collect as many layers as possible from damage & control samples from each type of surface involved into a paper fold