Textiles in Forensic Work

Flashcards covering key concepts from the lecture on textiles in forensic work.

Fibers

Elongate structures whose length exceeds their breadth. Divided into natural or artificial

Natural Fibers

Animal, mineral, vegetable

Artificial Fibers

Fibers made from synthetic materials or regenerated from natural substances; an example is rayon.

Most common fiber type is

polyester

Textile fabrics – rarely manufactured from individual fibers but from a

yarn

Yarn

a strand of textile fiber in form suitable for wearing, knitting, braiding, webbing or otherwise fabrication into fabric

Fabric

any material woven, knitted, felted or otherwise produced from, or in combination with any natural or manufactured fiber, yarn, or substitute

Types of fabrics

woven, knitted, non-woven

Fiber Transfer

Process wherein fibers are transferred from one surface to another during contact.

T/F it is easy to differentiate between primary and secondary transfer

F

Primary Transfer

Direct transfer of fibers from a donor item to a recipient item.

Secondary Transfer

Transfer of fibers from a donor item to one recipient and then to another recipient.

Mechanical Fit

Matching physical characteristics of fibers or fabrics that can indicate a common source.

Microscopy

A method used to identify and compare fibers based on their physical properties.

Persistence

The likelihood that fibers will remain on a surface after being transferred.

Contamination

Unwanted transfer of fibers between items which can compromise forensic evidence.

GIFT Principle

Get It First Time; the guideline for timely and proper evidence collection.

Steps involved in lab examination

• Transfer potential

• Construction parameters (to ensure all fiber types in fabric are sampled)

• Preliminary analysis – low-power microscopy

• Representative yarns and fibers prepared in suitable microscopic mountant

Typical features assessed:

• Fiber diameter and variation along fiber length

• Fiber shape

• Surface features

• Internal details (presence, amount, size, shape and distribution of delustrant)

• Color

• fluorescence

Factors affecting transfer

• Fiber Type Fiber

• Morphology and Thickness

• Fabric texture and construction

• Area of contact

• Number of contacts

• Force of pressure or contact

Most to least shedable fabrics

Wool > acrylic > cotton > viscose > polyester > nylon

With higher pressure, greater proportion of ____ fiber transfer

short

Transfer properties of item can change due to

Washing, wear, other treatments

Garments will shed ____ through time

less

persistence

Whether or not fibers will be found after a transfer

Factors that affect persistence

• Force of pressure of contact – persistence is poorer when contact is light

• Location of contact – fibers are lost more rapidly from areas which are more prone to contact with other surfaces

• Wearing of the recipient garment – fiber are lost more rapidly when the wearer moves after contact

• Placement of other clothing in contact with area of transfer fibers are lost more rapidly when other clothing is worn over or on top of recipient

Fiber binding states

loosely bound, bound, strongly bound

Methods of recovery should be:

simple, quick, efficient, preserve the evidence, allow easy subsequent searching

Methods of recovery

visual search, surface debris taping, combing, scraping, vacumming

Contamination measures on-site

• Victim and accused should be transported in separate cars

• Victim and accused should be interviewed / examined in separate rooms

• Clothing should be packaged in separate rooms by different individuals

• Protective clothing should be used at crime scene

Target fibers are

Those fibers which are sheddable and are of a color which can make them suitable for searching purposes

Delustrant

Material added to synthetic fibers to reduce their luster.

IR Spectroscopy

Technique used to identify polymers in fibers by measuring their infrared light absorbance.

Pyrolysis

Decomposition of a molecule by heat, used to analyze fiber composition.

Raman Spectroscopy

Technique that uses laser light to analyze the chemical composition of fibers.

Total Fiber Analysis

Includes fiber type identification, color analysis, and microscopic examination.

Yarn

A strand of textile fiber suitable for forming fabrics through various methods.

Fabric

Material produced by weaving, knitting, or bonding fibers together.

Transfer Types

Categories of fiber transfers including primary and secondary.

Microscopy

Simplest yet most useful method of fiber ID and comparison. Under simple white light high-power microscopy, naturally occurring fibers can be ID. More challenging with synthetic fibers

Most important characteristic for comparison

color (hue, saturation, lightness)

Types of physical properties

• Color

• Diameter

• Delustrant

• Cross-sectional shape

• Draw marks

• Fine striations

• Twist/convolutions/crimps

• Voids

• Internal channels

retardation

Synthetic fibers – different RI between parallel axis and the perpendicular axis of fiber

If parallel RI > than perpendicular RI

fiber has positive elongation

advantages of IR spectroscopy

• Minimal sample prep

• Better signal-to-noise ratio

• Provide higher precision

• Cleaner spectra

• Used on very small samples

• Provide additional potential discrimination

disadvantages of pyrolysis

• Destructive

• Requires large samples

• Reproducibility

In forensic casework fiber damage seen as:

• Mechanical damage (cutting by sharp-edged objects)

• Environmental damage (normal use)

• Influence of high temperature (and pressure)

• Microorganisms (bacteria and fungi)

T/F Often difficult for examiner to differentiate between normal “wear and tear” and other kinds of mechanical damage

T

Known factors

• Circumstances of case

• Number of types of matching fibers

• Time that has elapsed before collection of evidence

• Whether or not there has been an apparent cross-transfer of fibers

• Methods used to conduct examinations

• Suitability of fiber types for recovery and comparison

• Number of matching fibers

• Extent of comparative information derived from samples

• Location of recovered fibers

Unknown factors

• Extent and force of contact

• Frequency of occurrence of matching fiber types

• Degree of certainty that specific items were definitely in contact

• Donor fiber shed potential