Fabrics are composed of Fabrics are composed of individual threads or yarns made individual threads or yarns made of fibersof fibersFibers are knitted, woven, bonded, Fibers are knitted, woven, bonded,

crocheted, felted, or knotted togethercrocheted, felted, or knotted togetherMost are either woven or knittedMost are either woven or knitted

Individual qualities of fabrics Individual qualities of fabrics include:include:Degree of stretchDegree of stretchAbsorbencyAbsorbencyWater repellenceWater repellenceSoftnessSoftnessDurabilityDurability

YarnYarnContinuous strand of fibers or filaments Continuous strand of fibers or filaments

that may be twisted togetherthat may be twisted togetherWarpWarp

Lengthwise yarn in fabricLengthwise yarn in fabricWeftWeft

Crosswise yarn in fabricCrosswise yarn in fabricBlendBlend

Fabric made up of two or more different Fabric made up of two or more different types of fiberstypes of fibers

PlainPlain Simplest & most common Simplest & most common

patternpattern Warp & weft yarns pass Warp & weft yarns pass

under each other under each other alternatelyalternately

Design resembles a Design resembles a checkerboardcheckerboard

SatinSatin Yarn interlacing isn’t Yarn interlacing isn’t

uniformuniform Interlacing weave passes Interlacing weave passes

over four or more yarnsover four or more yarns Creates long floatsCreates long floats

TwillTwill Warp yarn is passed over Warp yarn is passed over

one to three weft yarns one to three weft yarns before going under one.before going under one.

Makes diagonal weave Makes diagonal weave patternpattern

Denim is most common Denim is most common example example

Knitted fabrics are made by Knitted fabrics are made by interlocking loops into a interlocking loops into a specific arrangementspecific arrangement

May be one continuous May be one continuous thread or a combinationthread or a combination

Yarn is formed into Yarn is formed into successive rows of loops & successive rows of loops & then drawn through another then drawn through another series of loops to make the series of loops to make the fabricfabric

All fabrics are long chains of All fabrics are long chains of monomers called polymersmonomers called polymersLimited number of natural fibers Limited number of natural fibers

but 1000s of artificial fibersbut 1000s of artificial fibersPolymer properties varyPolymer properties vary

Chemical structure of monomers Chemical structure of monomers varyvary

Chemical bond of monomers varyChemical bond of monomers varyBecause of these differences, Because of these differences,

polymers can be distinguished polymers can be distinguished form one another forensicallyform one another forensically

Characteristics that can be used to identify & Characteristics that can be used to identify & compare fibers as forensic evidence:compare fibers as forensic evidence:Fiber cross sectionFiber cross sectionChemical structureChemical structureMicroscopic observationMicroscopic observationBurn testsBurn testsThermal decompositionThermal decompositionChemical testsChemical testsDensityDensityRefractive indexRefractive indexFluorescence Fluorescence

Synthetic fibers are forced out Synthetic fibers are forced out of a nozzle when they are hot of a nozzle when they are hot & then woven& then woven

Holes of the nozzle are not Holes of the nozzle are not always round so fiber filament always round so fiber filament may have a unique shape in may have a unique shape in the cross sectionthe cross section

Microscopic observationMicroscopic observationCompare color, diameter, twist, Compare color, diameter, twist,

number of strands, etcnumber of strands, etcThermal DecompositionThermal Decomposition

Use heat to break down the fiber Use heat to break down the fiber to basic monomersto basic monomersExample: acetate fibers decompose Example: acetate fibers decompose

to form acetic acidto form acetic acidBurn Tests – how fibers burnBurn Tests – how fibers burn

OdorOdorColor of flameColor of flameColor of smokeColor of smokeAppearance of residueAppearance of residue

Chemical TestsChemical TestsSolubility & decompositionSolubility & decomposition

Separates waft & weftSeparates waft & weftDensityDensity

Mass of an object divided by its Mass of an object divided by its volumevolume

Especially useful for single fibersEspecially useful for single fibersNondestructive to fibersNondestructive to fibers

Refractive indexRefractive indexMeasurement of the bending of Measurement of the bending of

light as it passes from air into a light as it passes from air into a solid or liquidsolid or liquid

Becke line is halo-like shadow Becke line is halo-like shadow appearing around an object appearing around an object immersed in a liquid of different immersed in a liquid of different refractive indexrefractive indexIf liquid & fiber have same If liquid & fiber have same

refractive value, fiber becomes refractive value, fiber becomes invisible because it bends light at invisible because it bends light at the same angle as liquidthe same angle as liquid

If liquid has lower or higher If liquid has lower or higher refractive value, the fiber can be refractive value, the fiber can be seenseenFiber has “halo” of a dark boundaryFiber has “halo” of a dark boundary

Becke line outside Becke line outside fiber edges means fiber edges means liquid has higher liquid has higher

refractive index than refractive index than fiberfiber

Becke line inside Becke line inside fiber image means fiber image means

liquid has lower liquid has lower refractive index than refractive index than

fiberfiber

FluorescenceFluorescenceAbsorption & reemission of light when exposed Absorption & reemission of light when exposed

to UV radiationto UV radiationExpose to both long & short wave radiation for Expose to both long & short wave radiation for

comparisoncomparisonMay be caused by chemical properties of fabric May be caused by chemical properties of fabric

itself or dyes/optical brighteners added to fabricitself or dyes/optical brighteners added to fabricUsed for comparing fibers as well as spotting Used for comparing fibers as well as spotting

fibers for collectionfibers for collection

Component of dyes can be separated & Component of dyes can be separated & matched to unknownmatched to unknown

More than 7,000 different dye formulationsMore than 7,000 different dye formulations

Chromatography is used to separate dyes for Chromatography is used to separate dyes for comparative analysiscomparative analysis

The way a fabric accepts a particular dye can The way a fabric accepts a particular dye can be used to identify & compare samplesbe used to identify & compare samples

Put clothing items individually in paper bagsPut clothing items individually in paper bags

Make sure that different items are not placed Make sure that different items are not placed on the same surface before being bagged.on the same surface before being bagged.

Make tape lifts of exposed skin areas & any Make tape lifts of exposed skin areas & any inanimate objectsinanimate objects

Removed fibers should be folded into a small Removed fibers should be folded into a small sheet of paper & stored in a paper bagsheet of paper & stored in a paper bag

Fiber evidence in court cases Fiber evidence in court cases can be used to connect the can be used to connect the suspect to the victim or to the suspect to the victim or to the crime scenecrime scene

In the case of Wayne Williams, In the case of Wayne Williams, fibers weighed heavily on the fibers weighed heavily on the outcome of the caseoutcome of the case

Williams was convicted in Williams was convicted in 1982 based on carpet fibers 1982 based on carpet fibers that were found in his home, that were found in his home, in his car, & on several in his car, & on several murder victimsmurder victims