Trace Evidence Unit: Fiber Evidence - Forensic Science

what evidence are textiles considered?

class evidence

what can fibers come from?

clothing, coats, carpets, furniture, curtains, bedding, insulation, rope, etc.

direct (primary) transfer

suspect directly to victim

secondary transfer

picked up from the environment and then transferred to the victim

when should you start collecting fiber evidence at a crime scene?

very early; most fiber evidence (95%) falls off or is lost from a crime scene within 24 hours

when using fiber evidence, forensic scientists want to determine the following:

type of fiber, fiber color, number of fibers found, where the fiber was found, what is the source of the fiber, are there multiple types of fiber, type of crime committed, time between crime and fiber

how can you collect fibers?

tweezers, post-its, vacuum, sticky tape, gel lifters

how can you search for fibers/hair?

oblique lighting

how can you analyzes fabrics/fibers?

look for physical properties—physical fit, pattern, weave, twist, color, diameter, cross-sectional shape

testing fibers when there is a limited amount of evidence

use a microscope

testing fibers where there is a large quantity of evidence

burning (compare melting points, odors, ash formation), solvents (compare solubility), chromatography (analysis of the dye composition)

fiber

smallest individual unit of textile

yarn

fibers spun together

textile

yarn is woven into different patterns

warp

length wide fibers side by side (vertical)

weft

crosswise wires (horizontal)

natural fibers

animals and plants

synthetic fibers

man-made

what are all animal fibers made of?

proteins

what 3 sources do animals provide fibers?

fur, hair, and silk webbing

what are examples of natural animal fibers?

sheep, goats, rabbits, alpacas, llamas, camels, silkworm caterpillars

sheep fiber

wool

goat fiber

cashmere, mohar

rabbit fiber

anogra

silkwarm caterpillar fiber

silk (from the cocoons)

what are examples of natural plant fibers?

seeds, leaf, stems

seed fiber

cotton

what does cotton look like?

ribbon; twists at irregular interverals

stem fibers

hemp (popular alternative to cotton), jute (used in rope, mats, handbags), flax (used in linen)

leaf fibers

manilla (relative of banana tree), sisal

what are synthetic fibers made of?

polymers (long strings of repeating chemical units called monomers)

how are synthetic fibers formed?

by extruding a fiber-forming substance through holes in a shower head-like device called a spinneret

what is an example of a regenerated fiber?

RAYON

RAYON

most common, first man-made fiber (1911); soft, versatile, derived from cellulose

examples of synthetic polymer fibers

nylon, acrylic, polyester, spandex

what is the fiber cross sectioning technique called?

jolliff method

what materials are needed for the jolliff method?

insulator shaft, needle threader, filler fiber

what are the steps to the jolliff method?

1. insert needle threader into insulator shaft (central hole)

2. insert ‘filler yarn’ through needle threader

3. insert sample fiber and gently pull (do not pull too far)

4. cut excess from both sides